Patent Application
20240209479
The present invention relates to an aluminum alloy forging material, an aluminum alloy forged product and a method of producing the same.
Priority is claimed on Japanese Patent Application No. 2022-200526, filed Dec. 15, 2022, and Japanese Patent Application No. 2023-191652, filed Nov. 9, 2023, the contents of which are incorporated herein by reference.
In recent years, aluminum alloys have been increasingly used for structural members for various products due to their light weight. For example, high-tensile steel has been used until now for automobile suspensions and bumper parts. On the other hand, high-strength aluminum alloy materials have come into use recently.
In addition, iron-based materials have been exclusively used for automobile parts, particularly, for example, elongated parts such as suspension arms. On the other hand, in recent years, they have been increasingly replaced with aluminum materials or aluminum alloy materials mainly in order to reduce the weight.
Since excellent corrosion resistance, high-strength and excellent processability are required for these automobile parts, Al—Mg—Si-based alloys particularly, A6061, are often used as aluminum alloy materials. Thus, in order to improve the strength, such automobile parts are produced by performing forging processing, which is one type of plastic processing, using an aluminum alloy material as a processing material.
In addition, recently, since it is necessary to reduce costs, suspension parts obtained by directly forging cast members as materials without extrusion and then subjecting them to a treatment (T6 treatment) of performing a solution treatment and an artificial aging treatment have begun to be put into practical use, and in order to further reduce the weight, the development of high-strength alloys to replace conventional A6061 has progressed (for example, refer to Patent Documents 1 to 3).
In recent years, the demand for aluminum has been increasing as automobiles have been required to be lighter in weight in order to reduce CO2 emissions. However, as a substitute for steel materials, it is necessary to further increase the strength. On the other hand, as one method for increasing the strength of aluminum, it is known to minimize formation of a recrystallized structure in the plastic processing and solution treatment process and to refine the crystal particle size.
However, the above Al—Mg—Si-based high-strength alloys have problems that a processed structure recrystallizes in the forging and heat treatment process, coarse crystal grains are formed, and thus it is not possible to obtain sufficiently high-strength. Therefore, in order to prevent formation of coarse recrystallized grains, recrystallization is sometimes prevented by adding Zr (zirconium) (for example, refer to Patent Documents 1 and 2).
However, addition of Zr is effective in preventing recrystallization, but it has the following problems.
In this manner, addition of Zr is effective in preventing recrystallization, but it is difficult to maintain the stability of strength.
The present invention has been made in view of such technical backgrounds, and an object of the present invention is to provide an aluminum alloy forging material and an aluminum alloy forged product which have excellent mechanical properties at room temperature, and a method of producing the same.
In order to address the above problems, the present invention provides the following aspects.
According to the present invention, it is possible to provide an aluminum alloy forging material and an aluminum alloy forged product which have excellent mechanical properties at room temperature, and a method of producing the same.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, in the drawings used in the following description, in order to facilitate understanding of features, feature parts are enlarged for convenience of illustration in some cases, and size ratios of components are not necessarily the same as actual ones. In addition, materials, dimensions and the like exemplified in the following description are examples, and the present invention is not necessarily limited thereto, and can be appropriately changed and implemented within ranges without changing the effects.
First, an aluminum alloy material according to the present invention will be described.
An aluminum alloy material according to one embodiment of the present invention is an aluminum alloy forging material having an alloy composition including Cu in a range of 0.30 mass % or more and 1.0 mass % or less, Mg in a range of 0.80 mass % or more and 1.8 mass % or less, Si in a range of 0.90 mass % or more and 1.9 mass % or less, Mn in a range of 0.30 mass % or more and 1.2 mass % or less, Fe in a range of 0.20 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, and having a ratio Fe/Mn of the Fe content to the Mn content (mass ratio) of less than 1.4, and with the remainder being made up of Al and unavoidable impurities, and an average crystal particle size of an alloy structure after forging is in a range of 50 μm or more and 120 μm or less, and an average crystal particle size of an AlFeSi(Mn)-based compound present at crystal grain boundaries is 3.0 μm or less.
An aluminum alloy material according to another embodiment of the present invention is an aluminum alloy forging material having an alloy composition including Cu in a range of 0.25 mass % or more and 0.55 mass % or less, Mg in a range of 0.85 mass % or more and 1.25 mass % or less, Si in a range of 1.02 mass % or more and 1.4 mass % or less, Mn in a range of 0.55 mass % or more and 1.0 mass % or less, Fe in a range of 0.32 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, and having a ratio Fe/Mn of the Fe content to the Mn content (mass ratio) of 0.3 or more and 1.2 or less, and with the remainder being made up of Al and unavoidable impurities, and an average crystal particle size of an alloy structure after forging is in a range of 50 μm or more and 120 μm or less, and an average crystal particle size of an AlFeSi(Mn)-based compound present at crystal grain boundaries is 3.0 μm or less.
The aluminum alloy material of the present embodiment corresponds to a 6000 series aluminum alloy in that it contains Mg and Si.
(Average Crystal Particle Size of Alloy Structure after Forging: 50 μm or More and 120 μm or Less)
The average crystal particle size of the alloy structure after the aluminum alloy forging material is forged is an index of the degree of crystal grain refinement. When the average crystal particle size of crystal grains is more than 120 μm, there is a risk of tensile properties and fatigue properties deteriorating according to the relationship of the Hall-Petch law. On the other hand, when the average crystal particle size is less than 50 μm, there is a risk of the toughness deteriorating, the impact resistance decreasing, and accordingly, processability decreasing. Therefore, the average crystal particle size of the alloy structure after forging is in a range of 5 μm or more and 120 μm or less.
If a large amount of the AlFeSi(Mn)-based compound is present at crystal grain boundaries of the alloy structure of the aluminum alloy forging material, there is a risk of mechanical properties (tensile properties/fatigue properties, etc.) deteriorating. Therefore, if an AlFeSi(Mn)-based compound is present at crystal grain boundaries of the alloy structure of the aluminum alloy forging material, the average crystal particle size is 3.0 μm or less.
An aluminum alloy material according to still another embodiment of the present invention is an aluminum alloy forging material having an alloy composition including Cu in a range of 0.25 mass % or more and 0.55 mass % or less, Mg in a range of 0.85 mass % or more and 1.25 mass % or less, Si in a range of 1.02 mass % or more and 1.4 mass % or less, Mn in a range of 0.61 mass % or more and 1.0 mass % or less, Fe in a range of 0.32 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less and having a ratio Fe/Mn of the Fe content to the Mn content (mass ratio) of 0.3 or more and 1.2 or less, and with the remainder being made up of Al and unavoidable impurities, and an average crystal particle size of an alloy structure after forging is in a range of 50 μm or more and 120 μm or less, and an average crystal particle size of an AlFeSi(Mn)-based compound present at crystal grain boundaries is 3.0 μm or less.
Next, an aluminum alloy forged product according to the present invention will be described.
As shown in
The aluminum alloy forged product 1a has an aluminum alloy composition including Cu in a range of 0.25 mass % or more and 0.55 mass % or less, Mg in a range of 0.85 mass % or more and 1.25 mass % or less, Si in a range of 1.02 mass % or more and 1.4 mass % or less, Mn in a range of 0.55 mass % or more and 1.0 mass % or less, Fe in a range of 0.32 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, and having a ratio Fe/Mn of the Fe content to the Mn content (mass ratio) of 0.3 or more and 1.2 or less, and with the remainder being made up of Al and unavoidable impurities. In addition, the cross section of a boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction in the aluminum alloy forged product 1a has an alloy structure that has an average crystal particle size in a range of 5 μm or more and 60 μm or less and does not contain an AlFeSi(Mn)-based compound having an average particle size of 2.0 μm or more, and has a fatigue limit at the number of repetitions to breakage of 107 cycles of 150 MPa or more in terms of fatigue properties at room temperature.
The aluminum alloy that is the material of the aluminum alloy forged product 1a according to the present embodiment corresponds to a 6000 series aluminum alloy in that it contains Mg and Si.
Cu has a function of finely dispersing a Mg—Si-based compound in the aluminum alloy and has a function of improving the tensile strength of the aluminum alloy by precipitating as an Al—Cu—Mg—Si-based compound including a Q phase. When the Cu content is within the above range, it is possible to improve mechanical properties of the aluminum alloy forged product 1a at room temperature.
Mg has a function of improving the tensile strength of the aluminum alloy. When Mg is solid-solutionized in an aluminum base phase or precipitates as a Mg—Si-based compound (Mg2Si) such as a β″ phase or an Al—Cu—Mg—Si-based compound (AlCuMgSi) including a Q phase, it contributes to strengthening of the aluminum alloy. In addition, Mg2Si has a function of minimizing formation of a CuAl2 phase in the aluminum alloy. When formation of a CuAl2 phase is minimized, the corrosion resistance of the aluminum alloy forged product 1a is improved. When the Mg content is within the above range, it is possible to improve the mechanical properties and corrosion resistance of the aluminum alloy forged product 1a at room temperature.
Like Mg, Si has a function of improving the mechanical properties and corrosion resistance of the aluminum alloy forged product 1a at room temperature. However, when excessive Si is added to the aluminum alloy, there is a risk of coarse primary crystal Si grains crystallizing and the tensile strength of the aluminum alloy decreasing. When the Si content is within the above range, it is possible to improve the mechanical properties and corrosion resistance of the aluminum alloy forged product 1a at room temperature while minimizing crystallization of primary crystal Si.
Mn has a function of improving the tensile strength of the aluminum alloy by forming fine granular crystals containing intermetallic compounds such as Al—Mn—Fe—Si and Al—Mn—Cr—Fe—Si in the aluminum alloy. When the Mn content is within the above range, it is possible to improve mechanical properties of the aluminum alloy forged product 1a at room temperature.
Fe has a function of improving the tensile strength of the aluminum alloy by crystallizing intermetallic compounds such as Al—Mn—Fe—Si, Al—Mn—Cr—Fe—Si, Al—Fe—Si, Al—Cu—Fe, and Al—Mn—Fe in the aluminum alloy as fine crystals. When the Fe content is within the above range, it is possible to improve mechanical properties of the aluminum alloy forged product 1a at room temperature.
Here, the relationship of Fe/Mn is 0.3 or more and 1.2 or less. When the relationship of Fe/Mn is 1.2 or less, it is possible to minimize crystallization of an AlFeSi-based compound with a size of 2.0 μm or more, and it is possible to improve mechanical properties.
Cr has a function of improving the tensile strength of the aluminum alloy by forming fine granular crystals containing intermetallic compounds such as Al—Mn—Cr—Fe—Si and Al—Fe—Cr in the aluminum alloy. When the Cr content is within the above range, it is possible to improve mechanical properties of the aluminum alloy forged product 1a at room temperature.
Ti has a function of refining aluminum alloy crystal grains and improving stretching processability. When the Ti content is less than 0.01 mass %, there is a risk of a sufficient crystal grain refinement effect not being obtained. On the other hand, when the Ti content is more than 0.1 mass %, there is a risk of coarse crystals being formed and stretching processability deteriorating. In addition, when a large amount of coarse crystals containing Ti are mixed into the aluminum alloy forged product 1a, the toughness may decrease. Therefore, the Ti content is 0.012 mass % or more and 0.035 mass % or less. The Ti content is preferably 0.015 mass % or more and 0.050 mass % or less.
B has a function of refining aluminum alloy crystal grains and improving stretching processability. When B is added to the aluminum alloy together with the above Ti, the crystal grain refinement effect is improved. When the B content is less than 0.0010 mass %, there is a risk of a sufficient crystal grain refinement effect not being obtained. On the other hand, when the B content is more than 0.030 mass %, there is a risk of coarse crystals being formed and mixed into the aluminum alloy forged product 1a as inclusions. In addition, when a large amount of coarse crystals containing B are mixed into the final aluminum alloy product, the toughness may decrease. Therefore, the B content is 0.0010 mass % or more and 0.030 mass % or less. The B content is preferably 0.0050 mass % or more and 0.025 mass % or less.
When the Zr content is 0.05 mass % or less, it precipitates in the forms of Al3Zr and Al—(Ti, Zr), and thus contributes to improving the strength of the aluminum alloy forged product 1a according to the recrystallization minimization effect and precipitation strengthening. When the Zr content is more than 0.050 mass %, it crystallizes as a coarse Zr compound, and thus there is a risk of the corrosion resistance of the aluminum alloy forged product 1a decreasing. Therefore, the Zr content is 0.050 mass % or less. In addition, in order to obtain the above recrystallization minimization effect and the effect of improving the strength of the forged product according to precipitation strengthening, the Zr content is preferably 0.0010 mass % or more.
The Zn content may be 0.250 mass % or less. When the Zn content is more than 0.250 mass %, MgZn2 is formed and precipitates from an Al base phase to the grain boundaries, causing intergranular corrosion, and the corrosion resistance of the aluminum alloy forged product decreases. Therefore, it is preferable that the Zn content be 0.250 mass % or less or that it not be included at all.
Unavoidable impurities are impurities that are unavoidably mixed into the aluminum alloy from raw materials or in the producing process. Examples of unavoidable impurities include Ni, Sn, and Be. It is preferable that the content of these unavoidable impurities be not more than 0.1 mass %.
For example, when the aluminum alloy forged product 1a is used as a suspension arm of a vehicle, the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction in the aluminum alloy forged product 1a according to the present embodiment is a part to which the minimum principal stress is applied. When the aluminum alloy forged product 1a is produced by forging processing, the cross section of the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction is a cross section in a direction parallel to a direction in which pressure is applied.
Here, the crystal particle size is a diameter (circle equivalent diameter) of a circle having the same area as the area of each crystal grain. The crystal grain area is calculated from images of crystal grains obtained using a scanning electron microscope (SEM) or an electron backscatter diffraction device (EBSD). The average crystal particle size is an average value of the circle equivalent diameters of 420 or more crystal grains. The average crystal particle size may be calculated using, for example, commercially available image analysis software.
The average crystal particle size of the alloy structure in the cross section of the central part of the aluminum alloy forged product 1a is an index of the degree of crystal grain refinement of the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction in the aluminum alloy forged product 1a. In the cross-sectional structure of the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction, when the average crystal particle size of crystal grains is more than 60 μm, there is a risk of tensile properties and fatigue properties deteriorating according to the relationship of the Hall-Petch law. On the other hand, when the average crystal particle size is less than 5 μm, there is a risk of the toughness deteriorating and the impact resistance decreasing. Therefore, in the cross-sectional structure of the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction, the average crystal particle size is in a range of 5 μm or more and 60 μm or less.
In the cross-sectional structure of the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction in the aluminum alloy forged product 1a, the standard deviation of the crystal particle size is not particularly limited and is preferably 30 or less. This is because, if the variation in crystal particle size is minimized so that the standard deviation of the crystal particle size is 30 or less, the impact resistance of the aluminum alloy forged product 1a increases. The standard deviation of the crystal particle size is more preferably 25 or less and still more preferably 20 or less.
The alloy structure in the cross section of the central part of the aluminum alloy forged product 1a is made not to contain an AlFeSi(Mn)-based compound having an average particle size of 2.0 μm or more. When an AlFeSi(Mn)-based compound having an average particle size of 2.0 μm or more is present, there is a risk of mechanical properties (tensile properties/fatigue properties, etc.) deteriorating.
In terms of fatigue properties at room temperature (20° C.), the cross section of the central part of the aluminum alloy forged product 1a has mechanical properties with a fatigue limit of 150 MPa or more at the number of repetitions to breakage of 107 cycles. When the fatigue limit is less than 150 MPa, there is a risk of the durability of parts decreasing.
(Proportion of Large-Angle Grain Boundaries with Crystal Orientation Difference of 15° or More is 27% or Less)
In the cross section of the central part of the aluminum alloy forged product 1a, the crystal grain boundary (large-angle grain boundary) with a crystal orientation difference of 15° or more is an index of the degree of progress of recrystallization of the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction in the aluminum alloy forged product 1a. The proportion of large-angle grain boundaries being 27% or less indicates that recrystallization is sufficiently minimized. When recrystallization is sufficiently minimized, mechanical properties of the elongated part 2 are improved. The proportion of large-angle grain boundaries can be obtained from an EBSD image.
Since the aluminum alloy that is the material of the aluminum alloy forged product 1a according to the present embodiment configured as described above has the above alloy composition, recrystallization is less likely to occur when the forged product is produced. Therefore, excessive coarse crystal grains are less likely to be formed. In addition, the cross section of the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction in the aluminum alloy forged product 1a according to the present embodiment has an alloy structure that has an average crystal particle size in a range of 5 μm or more and 60 μm or less and does not contain an AlFeSi(Mn)-based compound having an average particle size of 2.0 μm or more. Therefore, the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction has improved tensile properties and fatigue properties, excellent toughness, and improved impact resistance. In addition, the aluminum alloy forged product 1a according to the present embodiment has a fatigue limit of 150 MPa or more at the number of repetitions to breakage of 107 cycles in the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction in the aluminum alloy forged product 1a, and has durability comparable to that of iron-based metal materials.
Since the aluminum alloy forged product 1a according to the present embodiment has high strength and durability in the boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction and is lightweight, it can be beneficially used for suspension arms of vehicles such as automobiles.
In the aluminum alloy forged product 1a according to the present embodiment shown in
An aluminum alloy forged product 1b shown in
An aluminum alloy forged product 1c shown in
An aluminum alloy forged product according to another embodiment of the present invention is an aluminum alloy forged product having an elongated part and a connecting part and having an aluminum alloy composition having an alloy composition including Cu in a range of 0.30 mass % or more and 1.0 mass % or less, Mg in a range of 0.80 mass % or more and 1.8 mass % or less, Si in a range of 0.90 mass % or more and 1.9 mass % or less, Mn in a range of 0.30 mass % or more and 1.2 mass % or less, Fe in a range of 0.20 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, and having a ratio Fe/Mn of the Fe content to the Mn content (mass ratio) of less than 1.4, and with the remainder being made up of Al and unavoidable impurities, and the cross section of the boundary part between the elongated part and the connecting part in the longitudinal direction has an alloy structure that has an average crystal particle size in a range of 5 μm or more and 60 μm or less and does not contain an AlFeSi(Mn)-based compound having an average crystal particle size of 2.0 μm or more, and has a fatigue limit at the number of repetitions to breakage of 107 cycles of 150 MPa or more in terms of fatigue properties at room temperature.
An aluminum alloy forged product according to still another embodiment of the present invention is an aluminum alloy forged product having an elongated part and a connecting part and having an alloy composition including Cu in a range of 0.25 mass % or more and 0.55 mass % or less, Mg in a range of 0.85 mass % or more and 1.25 mass % or less, Si in a range of 1.02 mass % or more and 1.4 mass % or less, Mn in a range of 0.61 mass % or more and 1.0 mass % or less, Fe in a range of 0.32 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, and having a ratio Fe/Mn of the Fe content to the Mn content (mass ratio) of 0.3 or more and 1.2 or less, and with the remainder being made up of Al and unavoidable impurities, and the cross section of the boundary part between the elongated part and the connecting part in the longitudinal direction has an alloy structure that has an average crystal particle size in a range of 5 μm or more and 60 μm or less and does not contain an AlFeSi(Mn)-based compound having an average crystal particle size of 2.0 μm or more, and has a fatigue limit at the number of repetitions to breakage of 107 cycles of 150 MPa or more in terms of fatigue properties at room temperature.
Next, a method of producing an aluminum alloy forged product according to the present embodiment will be described.
The method of producing an aluminum alloy forged product according to the present embodiment includes, for example, a molten metal forming process, a casting process, a homogenization heat treatment process, a forging process, a solution treatment process, a quenching treatment process, and an aging treatment process. Among these, the solution treatment process may be performed as necessary, and is not an essential process.
The molten metal forming process is a process in which raw materials are dissolved to obtain an aluminum alloy molten metal whose composition has been adjusted. The composition of the aluminum alloy molten metal has the same composition of the aluminum alloy forged product. That is, a 6000 series aluminum alloy molten metal is obtained by preparing the alloy composition containing Cu in a range of 0.25 mass % or more and 0.55 mass % or less, Mg in a range of 0.85 mass % or more and 1.25 mass % or less, Si in a range of 1.02 mass % or more and 1.4 mass % or less, Mn in a range of 0.55 mass % or more and 1.0 mass % or less, Fe in a range of 0.32 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, and having a ratio Fe/Mn of the Fe content to the Mn content (mass ratio) of 0.3 or more and 1.2 or less, and with the remainder being made up of Al and unavoidable impurities.
When subsequent processes are performed using the aluminum alloy molten metal having the above composition, it is possible to obtain an Al—Mg—Si-based aluminum alloy forged product that does not easily recrystallize and has excellent mechanical properties at room temperature. Here, a new aluminum ingot is aluminum with a concentration of 99% or more obtained by performing electrolysis called electrolytic refining on alumina produced from minerals.
An aluminum alloy molten metal can be obtained by heating and melting an aluminum alloy. In addition, it may be formed by melting a mixture containing a compound containing a single element or two or more elements serving as raw materials for the aluminum alloy in a proportion at which a desired aluminum alloy is formed. For example, in order to control the crystal particle size of the aluminum alloy produced in the casting process, Ti or B may be mixed as a crystal grain refining material such as an Al—Ti—B rod.
In addition, an aluminum alloy molten metal may be obtained by using 10% or more of a 1000 series, 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, or 7000 series aluminum alloy scrap material as a raw material for the aluminum alloy molten metal, and the remainder being a new aluminum ingot, and the above additive elements, and dissolving these materials and adjusting the composition. In this case, it is possible to obtain an Al—Mg—Si series aluminum alloy forged product that does not easily recrystallize and has excellent mechanical properties at room temperature. Here, for example, a new aluminum ingot is aluminum with a purity of 99% or more obtained by performing electrolysis called electrolytic refining on alumina produced from minerals.
In the casting process, an aluminum alloy cast product is obtained by cooling an aluminum alloy molten metal (liquid phase) and coagulating it into a solid (solid phase). In the casting process, for example, a horizontal continuous casting method can be used.
Here, the horizontal continuous casting device that can be used to produce the aluminum alloy cast product of the present embodiment is shown in
Here,
The horizontal continuous casting device 10 shown in
The molten metal receiving part 11 is composed of a molten metal inflow part 11a that receives an aluminum alloy molten metal M obtained in the molten metal forming process, a molten metal holding part 11b, and an outflow part 11c toward a hollow part 21 of the mold 12.
The molten metal receiving part 11 maintains the level of the upper liquid surface of the aluminum alloy molten metal M at a position higher than the upper surface of the hollow part 21 of the mold 12, and in the case of continuous casting, stably distributes the aluminum alloy molten metal M to each mold 12.
The aluminum alloy molten metal M held in the molten metal holding part 11b in the molten metal receiving part 11 is poured into the hollow part 21 of the mold 12 through a pouring path 13a provided at the refractory plate 13. Then, the aluminum alloy molten metal M supplied into the hollow part 21 is cooled and solidified by a cooling device 23 to be described below, and is drawn out from the other end side 12b of the mold 12 as an aluminum alloy rod B which is a coagulated ingot.
A drawer drive device (not shown) that draws out the cast aluminum alloy rod B at a certain speed may be installed on the other end side 12b of the mold 12. In addition, it is preferable that a synchronous cutting machine (not shown) that cuts the continuously drawn aluminum alloy rod B at an arbitrary length be installed.
The refractory plate 13 is a member that blocks heat transfer between the molten metal receiving part 11 and the mold 12, and may be made of a material, for example, calcium silicate, alumina, silica, a mixture of alumina and silica, silicon nitride, silicon carbide, graphite or the like. Such a refractory plate 13 can also be composed of a plurality of layers made of different constituent materials.
The mold 12 is a hollow cylindrical member in the present embodiment, and is, for example, formed of one material selected from among aluminum, copper, and alloys thereof or a combination of two or more thereof. For such a material of the mold 12, an optimal combination may be selected in consideration of thermal conductivity, heat resistance, and mechanical strength.
The hollow part 21 of the mold 12 is formed to have a circular cross section in order to make the aluminum alloy rod B to be cast into a cylindrical rod shape, and the mold 12 is held such that the mold central axis (central axis) C passing through the center of the hollow part 21 is substantially in the horizontal direction.
An inner circumferential surface 21a of the hollow part 21 of the mold 12 is formed at an elevation angle of 0° to 3° (more preferably 0° to 1°) with respect to the mold central axis C in the casting direction (refer to
When the elevation angle is less than 0°, there is a risk of casting becoming difficult because resistance is applied on the other end side 12b, which is the mold outlet, when the aluminum alloy rod B is drawn out from the mold 12. On the other hand, when the elevation angle is more than 3°, there is a risk of the degree of contact of the inner circumferential surface 21a with the aluminum alloy molten metal M becoming insufficient, the effect of removing heat from the aluminum alloy molten metal M and the coagulated shell obtained by cooling and solidifying it to the mold 12, and thus coagulation becoming insufficient. As a result, this is not preferable because there is a risk of a re-melted surface occurring on the surface of the aluminum alloy rod B or casting troubles such as spraying of the uncoagulated aluminum alloy molten metal M from the end of the aluminum alloy rod B.
Here, in addition to the circular shape in the present embodiment, the cross-sectional shape (the planar shape when the hollow part 21 of the mold 12 is viewed from the other end side 21b) of the hollow part 21 of the mold 12 may be selected from among, for example, a triangular or rectangular cross-sectional shape, a polygonal shape, a semicircular shape, an elliptical shape, and an irregular cross-sectional shape having no symmetric axis or symmetric surface, according to the shape of the aluminum alloy rod to be cast.
On the one end side 12a of the mold 12, a fluid supply pipe 22 through which a lubricating fluid is supplied into the hollow part 21 of the mold 12 is arranged. As the lubricating fluid supplied from the fluid supply pipe 22, any one or more lubricating fluids selected from among gas lubricants and liquid lubricants can be used. When both a gas lubricant and a liquid lubricant are supplied, it is preferable to provide respective fluid supply pipes separately. The lubricating fluid supplied under pressure from the fluid supply pipe 22 is supplied into the hollow part 21 of the mold 12 through an annular lubricant supply port 22a.
In the present embodiment, the pressure-fed lubricating fluid is supplied from the lubricant supply port 22a to the inner circumferential surface 21a of the mold 12. Here, the liquid lubricant may be heated to become a decomposed gas and supplied to the inner circumferential surface 21a of the mold 12. In addition, a porous material may be disposed in the lubricant supply port 22a and the lubricating fluid may be exuded to the inner circumferential surface 21a of the mold 12 through the porous material.
Inside the mold 12, the cooling device 23 which is a cooling unit configured to cool and solidify the aluminum alloy molten metal M is formed. The cooling device 23 of the present embodiment includes a cooling water cavity 24 that accommodates cooling water W for cooling the inner circumferential surface 21a of the hollow part 21 of the mold 12 and a cooling water injection path 25 that communicates between the cooling water cavity 24 and the hollow part 21 of the mold 12.
The cooling water cavity 24 is formed in an annular shape so that it surrounds the hollow part 21 outside the inner circumferential surface 21a of the hollow part 21 inside the mold 12, and the cooling water W is supplied through a cooling water supply pipe 26.
In the mold 12, the inner circumferential surface 21a is cooled with the cooling water W accommodated in the cooling water cavity 24, heat of the aluminum alloy molten metal M filled into the hollow part 21 of the mold 12 is removed from the surface of the mold 12 that comes into contact with the inner circumferential surface 21a, and a coagulated shell is formed on the surface of the aluminum alloy molten metal M.
In addition, in the cooling water injection path 25, cooling water W is directly applied toward the aluminum alloy rod B from a shower opening 25a facing the hollow part 21 on the other end side 12b of the mold 12, and the aluminum alloy rod B is cooled. The longitudinal cross-sectional shape of the cooling water injection path 25 may be, for example, a semicircular shape, a pear shape, or a horseshoe shape, in addition to the circular shape in the present embodiment.
Here, in the present embodiment, the cooling water W supplied through the cooling water supply pipe 26 is first accommodated in the cooling water cavity 24 and cools the inner circumferential surface 21a of the hollow part 21 of the mold 12, and additionally, the cooling water W in the cooling water cavity 24 is injected toward the aluminum alloy rod B through the cooling water injection path 25, but it can be supplied through cooling water supply pipes of respective separate systems.
The length from the position at which the extension line of the central axis of the shower opening 25a of the cooling water injection path 25 touches the surface of the cast aluminum alloy rod B to the contact surface between the mold 12 and the refractory plate 13 is referred to as an effective mold length L, and this effective mold length L is preferably, for example, 10 mm or more and 40 mm or less. When the effective mold length L is less than 10 mm, casting is not possible because a favorable film is not formed, and when the effective mold length L is more than 40 mm, this is not preferable because there is a risk that the effect of forced cooling becomes weak, coagulation by the mold wall becomes dominant, the contact resistance between the mold 12 and the aluminum alloy molten metal M or the aluminum alloy rod B becomes large, cracks occur on the casting surface, breakage occurs inside the mold, and thus casting becomes unstable.
It is preferable that operations of supply of the cooling water W to the cooling water cavity 24 and injection of the cooling water W from the shower opening 25a of the cooling water injection path 25 can be controlled by a control signal from a control device (not shown).
The cooling water cavity 24 is formed such that an inner bottom surface 24a near the hollow part 21 of the mold 12 is parallel to the inner circumferential surface 21a of the hollow part 21 of the mold 12.
Parallel here means that the inner circumferential surface 21a of the hollow part 21 of the mold 12 is formed at an elevation angle of 0° to 3° with respect to the inner bottom surface 24a of the cooling water cavity 24, that is, the inner bottom surface 24a is tilted by more than 0° and up to 3° with respect to the inner circumferential surface 21a.
As shown in
The mold 12 may be formed such that the thickness t of the cooling wall part 27 of the mold 12, that is, the distance between the inner bottom surface 24a of the cooling water cavity 24 and the inner circumferential surface 21a of the hollow part 21 of the mold 12 is, for example, in a range of 0.5 mm or more and 3.0 mm or less, and preferably 0.5 mm or more and 2.5 mm or less. In addition, the material for forming the mold 12 may be selected so that the thermal conductivity of at least the cooling wall part 27 of the mold 12 is in a range of 100 W/m·K or more and 400 W/m·K or less.
In
Since the aluminum alloy rod B is drawn out at a certain speed by a drawer drive device (not shown) installed near the other end side 12b of the mold 12, the elongated aluminum alloy rod B is formed by continuously casting. The drawn aluminum alloy rod B is cut into a desired length by, for example, a synchronous cutting machine (not shown).
Here, the composition ratio of the cast aluminum alloy rod B can be confirmed, for example, by a method using an optical emission spectrometer (device example: PDA-5500, commercially available from Shimadzu Corporation, Japan) as described in “JIS H 1305.”
The difference between the height of the liquid level of the aluminum alloy molten metal M stored in the molten metal receiving part 11 and the height from the upper inner circumferential surface 21a of the mold 12 is preferably 0 mm to 250 mm (more preferably, 50 mm to 170 mm). Within this range, the pressure of the aluminum alloy molten metal M supplied into the mold 12 and lubricating oils and gases vaporized from the lubricating oil are appropriately balanced so that castability is stabilized.
As the liquid lubricant, vegetable oils, which are lubricating oils, can be used. Examples thereof include rapeseed oil, castor oil, and salad oil. These are preferable because they have less impact on the environment.
The lubricating oil supply rate is preferably 0.05 mL/min to 5 mL/min (more preferably 0.1 mL/min or more and 1 mL/min or less). When the supply rate is too low, there is a risk of the aluminum alloy molten metal M of the aluminum alloy rod B not solidifying and leaking from the mold 12 due to insufficient lubrication. When the supply rate is too high, there is a risk of an excess component being mixed into the aluminum alloy rod B and internal defects occurring.
The casting speed, which is a speed at which the aluminum alloy rod B is pulled out from the mold 12, is preferably 200 mm/min or more and 1,500 mm/min or less (more preferably 400 mm/min or more and 1,000 mm/min or less). This is because, when the casting speed is within this range, the network structure of crystals formed by casting becomes uniform and fine, the resistance to deformation of the aluminum fabric at a high temperature increases, and the high-temperature mechanical strength is improved.
The amount of cooling water injected from the shower opening 25a of the cooling water injection path 25 is preferably 10 L/min or more and 50 L/min or less (more preferably 25 L/min or more and 40 L/min or less) per mold. When the amount of cooling water is smaller than this range, there is a risk of the aluminum alloy molten metal M not solidifying and leaking from the mold 12. In addition, there is a risk of the surface of the cast aluminum alloy rod B being re-melted and a non-uniform structure that remains as an internal defect being formed. On the other hand, when the amount of cooling water is larger than this range, there is a risk of too much heat being removed from the mold 12 and coagulation occurring during progress.
The average temperature of the aluminum alloy molten metal M flowing into the mold 12 from the inside of the molten metal receiving part 11 is preferably, for example, 650° ° C. or higher and 750° C. or lower (more preferably 680° C. or higher and 720° C. or lower). When the temperature of the aluminum alloy molten metal M is too low, there is a risk of coarse crystals being formed in the mold 12 and in front of it, and incorporated into the aluminum alloy rod B as internal defects. On the other hand, when the temperature of the aluminum alloy molten metal M is too high, there is a risk of a large amount of hydrogen gas being likely to be incorporated into the aluminum alloy molten metal M, and incorporated into the aluminum alloy rod B as pores, and creating an internal cavity.
Then, in the cooling wall part 27 of the mold 12, when the heat flux value per unit area from the aluminum alloy molten metal M in the hollow part 21 toward the cooling water W in the cooling water cavity 24 is in a range of 10×105 W/m2 or more and 50×105 W/m2 or less, it is possible to prevent the aluminum alloy rod B from burning.
The cooling wall part 27 of the mold 12 receives heat due to heat removal from the aluminum alloy molten metal M, and performs heat exchange by cooling this heat with the cooling water W accommodated in the cooling water cavity 24, but regarding the state of this heat exchange, as shown in the illustrative diagram shown in
Based on the mold material, thickness, and temperature measurement data with which favorable results are obtained even if the amount of lubricating oil is reduced during casting, when the cooling wall part 27 of the mold 12 is formed such that the heat flux value per unit area is 10×105 W/m2 or more, it is possible to prevent the cast aluminum alloy rod B from burning. In addition, the heat flux value per unit area is preferably 50×105 W/m2 or less.
In order for the cooling wall part 27 of the mold 12 to have such a heat flux value range, the mold 12 may be formed such that the thickness t of the cooling wall part 27 of the mold 12 is, for example, in a range of 0.5 mm or more and 3.0 mm or less. In addition, the thermal conductivity of at least the cooling wall part 27 of the mold 12 may be in a range of 100 W/m·K or more and 400 W/m·K or less.
When the aluminum alloy rod B according to the present embodiment is produced, the aluminum alloy molten metal M stored in the molten metal receiving part 11 is continuously supplied into the hollow part 21 from the one end side 12a of the mold 12 using the above horizontal continuous casting device 10. In addition, the cooling water W is supplied into the cooling water cavity 24, and a lubricating fluid, for example, a lubricating oil, is also supplied from the fluid supply pipe 22.
Then, the aluminum alloy molten metal M supplied into the hollow part 21 is cooled and coagulated under conditions in which the heat flux value per unit area in the cooling wall part 27 is 10×105 W/m2 or more, and the aluminum alloy rod B is cast. In addition, when the aluminum alloy rod B is cast, it is preferable that the wall surface temperature of the cooling wall part 27 of the mold 12 cooled with the cooling water W be set to be 100° C. or lower.
The aluminum alloy rod B obtained in this manner is cooled and coagulated under conditions in which the heat flux value per unit area in the cooling wall part 27 is 10×105 W/m2 or more, and thus fixation of reaction products, for example, carbides, due to contact between the lubricating oil gas and the aluminum alloy molten metal M, is curbed. Thereby, there is no need to cut off and remove carbides and the like on the surface of the aluminum alloy rod B, and the aluminum alloy rod B can be produced with a high yield.
In the casting process for obtaining a cast product from the aluminum alloy molten metal M, known continuous casting methods such as a vertical continuous casting method can be used without being limited to the above horizontal continuous casting method. Vertical continuous casting methods are classified into a float method and a hot top method depending on the method of supplying the aluminum alloy molten metal M into the mold (the mold 12), but a case using a hot top method will be briefly described below.
The casting device used in the hot top method includes a mold, a molten metal receiving container (header) and the like. The molten metal supplied to the molten metal receiving part passes through a tap outlet, the flow rate is adjusted when the molten metal passes through a header, the molten metal enters a cylindrical mold that is installed substantially horizontally, and forcedly cooled therein, and a coagulated shell is formed on the outer surface of the molten metal.
In addition, cooling water is directly released to the cast product drawn out from the mold, and the cast product is continuously drawn out while coagulation of the metal progresses to the inside of the cast product. Generally, the mold is made of a metal member with favorable thermal conductivity and has a hollow structure for introducing a refrigerant to the inside of the mold.
The refrigerant used may be appropriately selected from among industrially available refrigerants, but water is recommended in consideration of ease of use.
The material of the mold used in the present embodiment is appropriately selected from among metals such as copper and aluminum, and graphite in consideration of heat transfer performance and durability in a part in contact with the molten metal. The header is generally made of a refractory material, and is installed above the mold. The material and size of the header may be appropriately selected depending on the component ranges of the alloy to be cast and dimensions of the cast product, and there are no particularly limitations.
The average cooling rate during casting may be appropriately selected from a generally recommended range, for example, 10 to 300° C./sec. The casting speed may be appropriately selected from a range generally used in horizontal continuous casting, for example, appropriately selected from a range of 200 to 600 mm/min.
According to the casting method described above, a uniform metal structure can be obtained even for medium- to large-sized cast products. The diameter of a target cast product is not particularly limited, and a bar with a diameter of 30 to 100 mm is suitably used.
The homogenization heat treatment process is a process in which the aluminum alloy cast product obtained in the casting process is subjected to a homogenization heat treatment, microsegregation caused by coagulation is homogenized, over-saturated solid-solution elements are precipitated and a metastable phase changes to an equilibrium phase.
Here, such a homogenization heat treatment process may be performed as necessary, and the process can directly proceed to the forging process after the casting process.
In the present embodiment, the cast product obtained in the casting process is subjected to a homogenization heat treatment in which it is held at a temperature of 370° ° C. or higher and 560° C. or lower for 2 hours to 10 hours. When the homogenization heat treatment is performed in this temperature range, since the cast product is sufficiently homogenized and solute atoms are sufficiently infiltrated, sufficient strength required in the subsequent aging treatment can be obtained.
The forging process is a process in which the aluminum alloy cast product after casting or after the homogenization heat treatment process is formed into a predetermined size to obtain a forging material, the obtained forging material is heated to a predetermined temperature, then pressurized with a press machine, and molded into a mold.
In the present embodiment, the forging material is forged at a heating temperature of 450° C. or higher and 560° C. or lower to obtain a forged product (for example, a suspension arm part of an automobile). In this case, the forging start temperature of the forging material is 450° C. or higher and 560° C. or lower. This is because, when the start temperature is lower than 450° C., the deformation resistance increases and sufficient processing is not possible, and when the start temperature is higher than 560° ° C., defects such as forging cracks and eutectic melting are more likely to occur.
The solution treatment process is a process in which the forged product obtained in the forging process is heated and formed into a solution, and thus distortion introduced in the forging process is reduced, and the solute element is solid-solutionized.
In the present embodiment, the forged product is subjected to a solution treatment in which it is held at treatment temperature of 530° ° C. or higher and 560° C. or lower for 0.3 hours or longer and 3 hours or shorter. The rate of temperature increase from room temperature to the above treatment temperature is preferably 5.0° C./min or more. When the treatment temperature is lower than 530° C., there is a risk of solid-solutionization of solute elements becoming insufficient. On the other hand, when the treatment temperature is higher than 560° C., solid-solutionization of solute elements is further promoted, but there is a risk of eutectic melting and recrystallization easily occurring. In addition, when the heating rate is less than 5.0° C./min, there is a risk of Mg2Si coarsely precipitating. On the other hand, when the treatment temperature is lower than 530° C., there is a risk of solutionization not proceeding and high-strength due to aging precipitation not being easily achieved.
The quenching treatment process is a process in which the forged product in a solid-solution state obtained in the solution treatment process is rapidly cooled to form an over-saturated solid solution.
In the present embodiment, the forged product is put into a water tank in which water (quenching water) is stored, and the forged product is immersed water to perform a quenching treatment. The water temperature in the water tank is preferably 20° C. or higher and 60° C. or lower. It is preferable that the forged product be put into the water tank so that the entire surface of the forged product comes into contact with water within 5 seconds or longer and 60 seconds or shorter after the solution treatment. The time for which the forged product is immersed in water varies depending on the size of the forged product, but is, for example, longer than 1 minute and 30 minutes or shorter.
The aging treatment process is a process in which the forged product is heated and held at a relatively low temperature to precipitate over-saturated solid-solutionized elements, and an appropriate hardness is imparted.
In the present embodiment, the forged product after the quenching treatment process is subjected to an aging treatment in which it is heated at a temperature of 170° C. or higher and 210° C. or lower and held at that temperature for 0.5 hours or longer and 7 hours or shorter. When the treatment temperature is lower than 170° C. or when the holding time is shorter than 0.5 hours, there is a risk of Mg2Si-based precipitates that improve the tensile strength not being able to grow sufficiently. On the other hand, when the treatment temperature is higher than 190° C. or when the holding time is longer than 7 hours, there is a risk of Mg2Si-based precipitates becoming too coarse and the tensile strength not being able to be improved sufficiently.
Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples.
First, aluminum alloy forging materials having alloy compositions (the remainder being made up of aluminum) shown in the following Table 1 were prepared. Continuous cast products having a circular cross section with a diameter of 49 mm were produced using the prepared aluminum alloy forging materials. Continuous cast products of Examples 1 and 5, continuous cast products of Examples 2 and 6, continuous cast products of Examples 3 and 7, and continuous cast products of Examples 4 and 8 had the same alloy composition, but conditions for the treatment process when the aluminum alloy forged product was produced were different. In addition, in Examples 9 to 23, the homogenization heat treatment process was not performed.
Next, the obtained continuous cast product was subjected to a homogenization heat treatment process (excluding Examples 9 to 23), a forging processing process, a solution treatment process, a quenching treatment process, and an artificial aging treatment process in that order to obtain the aluminum alloy forged product 1a having the shape shown in
The following evaluations were performed on the aluminum alloy forging materials of Examples 1 to 23 and Comparative Examples 1 to 3, and the boundary part 2b of the elongated part 2 in the length direction in the aluminum alloy forged product 1a. The evaluation results are shown in the following Table 3.
Here, for refinement evaluation of forging materials and forged products, a plate-like component (7 mm×7 mm×thickness 2 mm) for evaluation test piece production was used as an evaluation test piece. On the surface of the collected evaluation test piece, using a scanning electron microscope-electron backscatter diffraction device (SEM-EBSD), the average crystal particle size, and the standard deviation of the crystal particle size were measured. The obtained average crystal particle size and the standard deviation of the crystal particle size were determined based on the following criteria, and crystal particle refinement and recrystallization/crystal coarsening were evaluated. Here, the measurement conditions for the SEM-EBSD were as follows: an acceleration voltage of 15 kV, a measurement pitch of 0.5 μm/px, an analysis area of 500×500 μm2, and a grain boundary definition angle of 15°.
It was evaluated whether the Fe/Mn ratio of the aluminum alloy forging material was within a range of 0.3 or more and 1.2 or less.
It was evaluated whether the average crystal particle size of the aluminum alloy forging material was within a range of 50 μm or more and 120 μm or less.
It was evaluated whether the average crystal particle size (size) of the AlFeSi compound of the aluminum alloy forging material was within a range of 3.0 μm or less.
(Determination criteria)
The number of AIMnFeSi compound particles with a size of 2.0 μm or more in the aluminum alloy forged product was measured.
The average crystal particle size and standard deviation of the alloy structure of the aluminum alloy forged product were measured.
The boundary part 2b between the elongated part 2 and the connecting part 4 in the longitudinal direction in the aluminum alloy forged product 1a was cut as shown in
The evaluation results of the above evaluation items were evaluated based on the following determination criteria.
As shown in Table 3, it was confirmed that, when the content of each element was set within a predetermined range, and each process was performed within the predetermined range of treatment conditions in the molten metal forming process, the casting process, the homogenization heat treatment process, the forging process, the solution treatment process, the quenching treatment process and the aging treatment process to produce an aluminum alloy forged product, it was possible to obtain the aluminum alloy forged product in which, in the central part of the elongated part in the longitudinal direction, when the variation in the particle size was minimized, sufficiently refined crystal grains could be formed and crystal coarsening due to recrystallization was minimized, and mechanical properties were excellent at room temperature.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-200526 | Dec 2022 | JP | national |
| 2023-191652 | Nov 2023 | JP | national |
