This application is based upon and claims the benefit of priority from Japanese patent application No. 2018-047692, filed on Mar. 15, 2018, the disclosure of which is incorporated herein in its entirety by reference.
The present disclosure relates to a method for manufacturing an aluminum alloy member.
A method for manufacturing an aluminum alloy member in which a casting made of an aluminum alloy containing Si is heated and held to be in a solid-liquid coexistence temperature region under a pressurized environment and then quenched is known. The method is disclosed in Japanese Unexamined Patent Publication No. 2017-155288.
The inventors of the present disclosure have found the following problems.
As shown in
The present disclosure suppresses deterioration in ductility of an aluminum alloy member.
A first exemplary aspect is a method for manufacturing an aluminum alloy member using an aluminum alloy casting material that contains 2.0 to 5.5 mass % of Cu, and 4.0 to 7.0 mass % of Si, in which a content of Mg is 0.5 mass % or less, a content of Zn is 1.0 mass % or less, a content of Fe is 1.0 mass % or less, a content of Mn is 0.5 mass % or less, and the balance is made of Al and inevitable impurities, and the method for manufacturing an aluminum alloy member includes: a heating and holding step of heating and holding the aluminum alloy casting material within a solid-liquid coexisting temperature region; and a quenching step of rapidly cooling the aluminum ally casting material after performing the heating and holding step, in which in a quenching preparation step between the heating and holding step and the quenching step, the aluminum alloy casting material is rapidly cooled at a cooling rate of 3° C./min or higher from the solid-liquid coexisting temperature region to a predetermined temperature lower than a liquid phase appearance temperature.
With such a structure, a eutectic Si crystallized at the time of casting is divided to be spheroidized, and subsequent coalescence and growth can be suppressed. Accordingly, the eutectic Si is coarsened, and is precipitated in a clumpy shape, such as a substantially spheroid shape, a substantially ellipsoidal shape or the like so that cleavage is prevented from occurring easily. Therefore, deterioration in ductility of an aluminum alloy member can be suppressed.
Further, in the heating and holding step and the quenching preparation step, the aluminum alloy casting material may be placed inside a pressurized furnace so as to be under a pressurized environment.
With such a structure, in the heating and holding step, the aluminum alloy casting material can be heated while applying compressive stress. In the quenching preparation step, likewise, the aluminum alloy casting material can be cooled while applying compressive stress. Accordingly, it is possible to steadily crush blowholes and vacancies that might be contained inside the aluminum alloy casting material. Therefore, deterioration in ductility of an aluminum alloy member can be suppressed.
Further, a nozzle is provided inside the pressurized furnace, and in the quenching preparation step, a cooling gas medium or mist may be blown from the nozzle to cool the aluminum alloy casting material rapidly.
With such a structure, a cooling gas medium removes the heat of the aluminum alloy casting material, or mist removes the same by coming into contact therewith and evaporating it.
Therefore, the aluminum alloy casting material can be cooled while it is placed under a pressurized environment.
Further, a contact part that contacts the aluminum alloy casting material is provided inside the pressurized furnace, the contact part has a shape conforming to a shape of the aluminum alloy casting material, a flow path is provided inside the contact part, and in the quenching preparation step, the aluminum alloy casting material may be rapidly cooled by making a cooling medium flow through the flow path.
With such a structure, the cooling medium removes heat from the aluminum alloy casting material through the contact part so that the aluminum alloy casting material can be rapidly cooled while it is placed under a pressurized environment.
The present disclosure can suppress deterioration in ductility of an aluminum alloy member.
The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure.
Specific embodiments to which the present disclosure is applied will be explained hereinafter in detail with reference to the drawings. However, the present disclosure is not limited to the embodiments shown below. Further, for clarifying the explanation, the following descriptions and the drawings are simplified as appropriate. In
A method for manufacturing an aluminum alloy member according to a first embodiment is described with reference to
First, as shown in
Next, the aluminum alloy casting material is heated and held during heating and holding time t1 to t2 so that an aluminum alloy casting material temperature T12 is maintained at a predetermined temperature within the solid-liquid coexisting temperature region TS to TL (heating and holding step ST2). Further, in the heating and holding step ST2, the pressure is continuously applied to the aluminum alloy casting material starting from the temperature-raising step ST1 described above.
Subsequently, the aluminum alloy casting material is cooled at a cooling rate Rc until the temperature thereof becomes a temperature TS-ΔT lower than the liquid phase appearance temperature TS by a predetermined differential temperature ΔT from a predetermined temperature within the solid-liquid coexisting temperature region TS to TL (quenching preparation step ST3). Lastly, the aluminum alloy casting material is further cooled to a normal temperature TR after the pressure of the space where the aluminum alloy casting material is placed is removed to reach the normal pressure (atmospheric pressure) (quenching step ST4).
Note that in the above quenching step ST4 of the method for manufacturing an aluminum alloy member according to the first embodiment, although the pressure of the space where the aluminum alloy casting material is placed starts to be removed from the start of the quenching step ST4, the start of removing the pressure may be within a range of from the middle of the quenching preparation step ST3 in which the aluminum alloy casting material is rapidly cooled to the liquid phase appearance temperature TS or lower to the completion of the quenching step ST4.
Next, a specific example of the above-described method for manufacturing an aluminum alloy member is described with reference to
First, a specific example of the temperature-raising step ST1 is described with reference to
The aluminum alloy casting material W1 is formed by melting an aluminum alloy, filling it to a mold, and solidifying it. The aluminum alloy casting material W1 has a predetermined shape, and is a part used for, for example, a vehicle. Examples of such parts include various parts such as an underbody member, and a wheel member, in addition to parts for engines such as a cylinder head. This aluminum alloy contains 2.0 to 5.5 mass % of Cu, and 4.0 to 7.0 mass % of Si, in which a content of Mg is 0.5 mass % or less, a content of Zn is 1.0 mass % or less, a content of Fe is 1.0 mass % or less, a content of Mn is 0.5 mass % or less and the balance is made of Al and inevitable impurities. Details of the chemical composition of the aluminum alloy will be described later.
Specifically, in the temperature-raising step ST1, the pressurized furnace 1 is hermetically sealed while the aluminum alloy casting material W1 is placed on the support base 4 (see
A specific example of the heating and holding step ST2 is described also with reference to
Specifically, together with this heating and holding of the aluminum alloy casting material W1, in the heating and holding step ST2, the pressure is continuously applied to the internal space 1c of the pressurized furnace 1 so that the furnace pressure Pc therein is maintained within a range of predetermined pressurized values. Since the aluminum alloy casting material W1 temperature T12 is maintained within the solid-liquid coexisting temperature region TS to TL, the pressure is applied to a blowhole through a liquid phase. Then, hydrogen in the blowhole is dissolved in an Al phase, and the size of the blowhole is reduced. As the pressure increases, the aluminum alloy casting material W1 is softened and then the internal defects thereof are crushed by receiving a compressive stress due to the furnace pressure Pc. These internal defects are, for example, vacancies and blowholes. The aluminum alloy casting material W1 temperature T12 is preferably within the solid-liquid coexisting temperature region TS to IL, and it is also preferred that a heating and holding temperature TSL be constant. It is preferred that the furnace pressure Pc be 0.6 Mpa or higher, or the heating and holding temperature TSL be the liquidus temperature TL or lower. This is because burning (melting) in the aluminum alloy casting material W1, or a sweating phenomenon in which melt is jetted in the surface of the casting, is less likely to occur at this pressure/temperature. The heating and holding temperature TSL is preferably the liquid phase appearance temperature TS or higher since the eutectic Si is divided and the spheroidizing thereof progresses.
Next, a specific example of the quenching preparation step ST3 is described with reference to
The cooling rate Rc is 3° C./min or higher. The differential temperature ΔT [° C.] may be 0 (zero) ° C. or higher, and may be, for example, 5° C., 10° C., 15° C., 20° C., or 25° C. or lower. The aluminum alloy casting material W1 is cooled at the cooling rate Rc of 3° C./min or higher until the temperature thereof becomes a temperature TS-ΔT lower than the liquid phase appearance temperature TS by a predetermined differential temperature ΔT from within the solid-liquid coexisting temperature region TS to TL. Note that when the temperature of the aluminum alloy casting material W1 is maintained within the solid-liquid coexisting temperature region TS to TL, in the metallic structure of the aluminum alloy casting material W1, the eutectic Si tends to become coarse or clumpy. On the other hand, when the temperature of the aluminum alloy casting material W1 is maintained at a temperature lower than the liquid phase appearance temperature TS, the eutectic Si tends to be less likely to become coarse or clumpy, and tends to maintain a fine and spherical shape. Therefore, the above-described cooling rate is maintained and thereby the temperature of the aluminum alloy casting material W1 drops to a temperature lower than the liquid phase appearance temperature TS before the eutectic Si becomes coarse or clumpy. This allows the eutectic Si to maintain a fine and spherical shape.
Specifically, in the quenching preparation step ST3, as shown in
Further, subsequent to the heating and holding step ST2, in the quenching preparation step ST3 it is preferred that the pressure be continuously applied to the internal space 1c of the pressurized furnace I so that the furnace pressure Pc therein is maintained within a range of predetermined pressurized values. The furnace pressure Pc is preferably maintained at a predetermined value, for example, 0.6 MPa or higher defects on the surface of the aluminum alloy casting material W1 due to a sweating phenomenon or burning (melting) in the aluminum alloy casting material W1 are less likely to occur at this value.
The mist nozzles 2 are connected to a tank (not shown) or the like that stores the fluid through a flow path (not shown), and the fluid is appropriately supplied to the mist nozzles 2 through a valve (not shown) or the like. The mist nozzles 2, the tank, the valve, and the flow path may be configured by using a mist spray device (not shown).
Next, a modified example of the quenching preparation step ST3 is described with reference to
Specifically, in this modified example of the quenching preparation step ST3, when the aluminum alloy casting material W1 is a cylinder head, air is preferably blown on the vicinity of the center of the chamber of that cylinder head. The fluid nozzles 3 can blow a fluid, such as air, water, nitrogen (N2), helium (He), argon (Ar), or the like, as a cooling gas medium on the aluminum alloy casting material W1. The support base 4 (see
Next, another modified example of the quenching preparation step ST3 is described with reference to
Specifically, in another modified example of the quenching preparation step ST3, the support base 4 includes a contact part 4a, a base 4b that supports the contact part 4a, and the flow path 4c through which the cooling medium CM1 can flow. It is preferred that the contact part 4a have a shape conforming to that of the aluminum alloy casting material W1, and be capable of coming into surface contact with the aluminum alloy casting material W1. The support base 4 is preferably made of a material having a thermal conductivity higher than that of other components of the pressurized furnace 1. Examples of such materials include Cu (copper), or Cu alloy.
As the cooling medium CM1, for example, water, oils, or the like can be used. In order to supply and discharge the cooling medium CM1 to and from the flow path 4c, a tank (not shown), an ejection device (not shown), or the like are preferably connected to the flow path 4c.
When an example of the aluminum alloy casting material W1 shown in
When the aluminum alloy casting material W1 and the contact part 4a of the support base 4 are brought to come into surface contact with each other, the contact part 4a removes heat from the aluminum alloy casting material W1 to cool the same. Further, when the cooling medium CM1 is supplied to the flow path 4c while the aluminum alloy casting material W1 and the contact part 4a are in surface contact with each other, the cooling medium CM1 removes heat from the aluminum alloy casting material W1 through the contact part 4a to cool the same. Note that it has been described that as the quenching preparation step ST3, a specific example of the quenching preparation step ST3 shown in
Next, a specific example of the quenching step ST4 is described. The aluminum alloy casting material W1 is further cooled to a normal temperature TR (quenching step ST4).
Specifically, in the quenching step ST4, after the removal of the pressure in the internal space 1c of the pressurized furnace 1 is started and the internal space 1c is confirmed to be at normal pressure (atmospheric pressure), the door 1b is opened so that the aluminum alloy casting material W1 can be taken outside the pressurized furnace 1, and the aluminum alloy casting material W1 is submerged in a water tank or the like to cool it rapidly.
Further, in the quenching step ST4, the aluminum alloy casting material W1 may be cooled by using the cooling method used in the quenching preparation step ST3 while the aluminum alloy casting material W1 is placed on the support base 4 in the internal space 1c of the pressurized furnace 1 continuously from the quenching preparation step ST3.
Note that in the example of the quenching step ST4, although the pressure starts to be removed from the internal space 1c of the pressurized furnace 1 from the start of the quenching step ST4, removal of the pressure from the internal space 1c of the pressurized furnace 1 may be started from the middle of the quenching preparation step ST3. The pressure is preferably removed in such a manner since the aluminum alloy casting material W1 can be rapidly cooled by submerging it in a water tank or the like and thereby the quenching step ST4 is shortened. Note that it is conceivable that the aluminum alloy member can maintain the shape or the like necessary for a desired aluminum alloy member even though defects due to burning and sweating phenomenon are likely to occur when the pressure is removed in such a manner. One reason for this is that since liquid phases which appeared at the liquid phase appearance temperature TS contain a lot of substances solidified in a non-equilibrium state, most of the liquid phases are dissolved in Al phases by carrying out the heating and holding step ST2. That is, the removal of the pressure from the internal space 1c of the pressurized furnace 1 may be started in the middle of the quenching preparation step ST3 in which the aluminum alloy member maintains the characteristic, the shape, or the like necessary for a desired aluminum alloy member, and in particular, the temperature of the aluminum alloy casting material W1 is preferably in the vicinity of the liquid phase appearance temperature TS.
As described above, since the cooling rate of the aluminum alloy casting material W1 in the quenching preparation step ST3 is 3° C./min, coalescence and coarsening of the eutectic Si are suppressed in the metallic structure of the aluminum alloy casting material W1. Therefore, the eutectic Si can maintain the fine and spherical shape. Accordingly, deterioration in ductility of an aluminum alloy member can be suppressed.
Next, a content of each component in the chemical composition of the aluminum alloy casting material W1 is described. When a content of Si in the chemical composition of the aluminum alloy casting material W1 is within a suitable range, a predetermined castability can be achieved. Accordingly, casting defects such as cracks and shrinkage cavities are less likely to occur in the aluminum alloy casting material W1 On the other hand, when the content of Si is too large, a large number of brittle Si particles crystallize in the aluminum alloy casting material W1, and thereby mechanical properties such as a breaking elongation and strength are likely to deteriorate. Therefore, the content of Si is preferably within a range of from 4.0% to 7.0%. The upper limit thereof is preferably any one of 6.5%, 6.0%, and 5.5%. The lower limit thereof is preferably any one of 4.5%, 5.0%, and 5.5%.
Further, when a content of Cu is within a suitable range, by heat treatment, CuAl2 is sometimes precipitated in the metallic structure of the aluminum alloy casting material Wl, or an MgCu-based compound is sometimes precipitated therein when Mg coexists in Al. In this way, mechanical strengths of Al, such as a tensile strength and 0.2% proof stress, can be improved. On the other hand, when the content of Cu is too large, ductility and toughness of the aluminum alloy casting material W1 may decrease. Therefore, the content of Cu is preferably within a range of from 2.0% to 5.5%. The upper limit thereof is preferably any one of 5.0%, 4.5%, and 4.0%. The lower limit thereof is preferably any one of 2.5%, 3.0%, 3.5%, 4.0% and 4.5%.
Further, when a content of Mg is within a suitable range, Mg atoms are dissolved in an Al base and thereby can strengthen the Al base. Further, Mg precipitates as Mg2Si by heat treatment, and thereby mechanical strengths, such as a tensile strength and 0.2% proof stress, of the aluminum alloy member can be improved. When the content of Mg is too large, ductility and toughness of the aluminum alloy casting material W1 may decrease. Therefore, the content of Mg is preferably 0.5% or less. Further, the content of Mg may be within a range of from 0.2% to 0.4%.
Further, when contents of Zn and Fe are too large, ductility and toughness of the aluminum alloy casting material W1 may decrease. Therefore, the contents of Zn and Fe are preferably 1.0% or less, respectively.
Further, when a content of Mn is within a suitable range, adverse effects of Fe on the aluminum alloy casting material W1 may be reduced. Further, a content of Mn is too large, ductility and toughness of the aluminum alloy casting material W1 may decrease. Therefore, the content of Mn is preferably 0.5% or less. Further, the content of Mn may be within a range of from 0.2% to 0.4%.
Note that in addition to the above-described components, for example, Sr, Na, Sb, Ti, B and the like may be contained in the aluminum alloy casting material W1. By containing the above-described component elements in this material, a eutectic Si or a primary crystal α-Al in the aluminum alloy casting material W1 is made fine, etc. so that the mechanical strength of the aluminum alloy casting material W1 can be improved. Further, as necessary, the aluminum alloy casting material W1 may modify the metallic structure by containing component elements other than those described above.
An aluminum alloy corresponding to the above-described chemical composition of the aluminum alloy casting material W1 is, for example, an AC2-type alloy defined by the JIS standard. The AC2-type alloys are, for example, AC2A, AC2B, AC2H or the like.
Next, a verification experiment on a cooling rate is described. As an aluminum alloy casting material, a rectangular parallelepiped test piece made of an alloy corresponding to AC2B was used. The size of the rectangular parallelepiped test piece is 30 mm in width, 95 mm in depth, and 35 mm in height.
In an example 1, this rectangular parallelepiped test piece was rapidly cooled in a quenching preparation step having the structure same as that of the specific example of the quenching preparation step ST3 (see
In a comparative example 1, this rectangular parallelepiped test piece was rapidly cooled in a quenching preparation step having the structure same as that of the example 1 other than the nozzles. The nozzle which was used in the comparative example 1 has one spray port, which blows nitrogen on this rectangular parallelepiped test piece. The flow rate of nitrogen blown from the nozzles in the comparative example 1 was respectively 3 L/min.
Next, another verification experiment on a cooling rate is described. As an aluminum alloy casting material, a cylinder head made of an alloy corresponding to AC2B was used. This cylinder head includes one cylinder and was used for this verification experiment.
In an example 2, this cylinder head was rapidly cooled in a quenching preparation step having the structure same as that of another modified example of the quenching preparation step ST3 (see
In a comparative example 2, this cylinder head was rapidly cooled in a quenching preparation step having the structure same as that of the example 2 other than the support base. The support base which was used in the comparative example 2 has the configuration same as that of the support base which was used in the example 2 except that it is made of a cast iron, specifically, a material corresponding to FC250 defined by the JIS standard.
Next, an experiment using a method for manufacturing an aluminum alloy member which was carried out to find manufacturing conditions suitable for the above-described method for manufacturing an aluminum alloy member according to the first embodiment is described. The method for manufacturing an aluminum alloy member which was used in this experiment is the same as the above-described method for manufacturing an aluminum alloy member according to the first embodiment other than the furnace pressure Pc, the heating and holding time t1 to t2 in the heating and holding step ST2, the aluminum alloy casting material W1 temperature T12, and the cooling rate Rc in the quenching preparation step ST3.
Specifically, an AC2B-type alloy was used as an aluminum alloy casting material. In the atmosphere, this aluminum alloy casting material was formed by naturally cooling and solidifying a molten metal made of an AC2B-type alloy after pouring it into a mold (JIS No. 7) having a boat-shaped cavity. In a heating and holding step corresponding to the heating and holding step ST2, a heating and holding time t1 to t2 (see
0.2% proof stress and a breaking elongation were measured for each of the aluminum alloy member test pieces which were manufactured as described above.
Specifically, first, the 0.2% proof stress and the breaking elongation with respect to the heating and holding time t1 to t2 were shown in
Further, the 0.2% proof stress and the breaking elongation with respect to the furnace pressure were shown in
Further, the 0.2% proof stress and the breaking elongation with respect to the heating and holding temperature of the aluminum alloy casting material W I were shown in
Further, the 0.2% proof stress and the breaking elongation with respect to the cooling rate were shown in
Further, metallic structures of each of the aluminum alloy member test pieces manufactured as described above were observed by using an optical microscope and a SEM (Scanning Electron Microscope). Further, an EPMA (Electron Probe Micro Analyzer) analysis was also conducted. Images photographed by performing the observation were shown in
Further, the manufacturing conditions shown in
As shown in
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Note that the present disclosure is not limited to the above-described embodiment. Changes can be made to the present disclosure without departing from the spirit of the invention. From the disclosure thus described, it will be obvious that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.
Number | Date | Country | Kind |
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2018-047692 | Mar 2018 | JP | national |