HIGH-STRENGTH ALUMINUM-MAGNESIUM SILICON ALLOY AND MANUFACTURING PROCESS THEREOF

Abstract

A high-strength aluminum-magnesium silicon alloy and its manufacturing process which includes a composition adjusting step to add vanadium (V) and zirconium (Zr) in an aluminum-magnesium silicon alloy to refine grains of the alloy; a material casting step, a material preheating step, a hot forging step and a heat treatment step to melt magnesium and silicon atoms into an aluminum base to cause a lattice distortion and achieve a strengthening effect and precipitate Mg2Si from the grains of the alloy, and the precipitated particles act as obstacles to dislocation movement. Therefore, the alloy product has a yield strength improved by 31%, the ultimate strength by 39%, the hardness by 34%, and the fatigue strength by 55%. Therefore, the alloy product can be used in components with a high strength requirement such as the aluminum alloy wheels and the control arms of a car suspension system.

Description

FIELD OF THE INVENTION

The present invention relates to a high-strength aluminum-magnesium silicon alloy, and more particularly to the technical area of improving the strength, hardness and fatigue resistance of an alloy product by adjusting the composition of trace elements of an alloy material and processing the alloy material with hot forging and heat treatment.

BACKGROUND OF THE INVENTION

As science and technology advance, aluminum alloys with the features of light weight, high corrosion resistance, easy molding and manufacture, high electric conductivity, high thermal conductivity and nontoxicity have been used extensively in different industries. Referring to the Chinese National Standards (CNS) and U.S. Aluminum Industry Standards, forged alloys can be divided into AA1xxx series pure aluminum, AA2xxx series aluminum-copper alloys, AA3xxx series aluminum-manganese alloys, AA4xxx series aluminum-silicon alloys, AA5xxx series aluminum-magnesium alloys, AA6xxx series aluminum-magnesium silicon alloys and AA7xxx series aluminum-zinc-magnesium alloys, etc.

In the aforementioned alloys, the AA6xxx series alloys can achieve a precipitation strengthening effect by adding a trace amount of magnesium (Mg) and silicon (Si) elements. The strength of the AA6xxx series alloys is moderate among these alloys, but the formability, acid resistance, weldability, and anodic treatment effect are very good, so that the AA6xxx series alloys are used extensively by manufacturers, and the common ones include the AA6053, AA6061, AA6063 and AA6151 alloys.

With reference to FIGS. 10 and 11, the AA6061 alloy generally has a chemical composition including 0.579 wt. % silicon (Si), 0.62 wt. % iron (Fe). 0.261 wt. % copper (Cu), 0.103 wt. % manganese (Mn), 1.024 wt. % magnesium (Mg), etc., and the AA6061 alloy ingot has grains with an average size or diameter of 125 μm (as shown in FIG. 12). Although the strength of the AA6061 alloy is incomparable with the strength of the AA2xxx series alloys and the AA7xxx series alloys, and the AA6061 alloy has better manufacturability, formability, weldability and corrosion resistance, and its extrusion speed is three to four times of the extrusion speed of the AA5056 alloy. Therefore, the alloy forging cost of the AA6061 alloy is lower than the alloy forging cost of the AA2xxx series alloys and the AA7xxx series alloys. In addition, the AA6061 alloy processed by T6 heat treatment can obtain excellent mechanical properties including a yield strength up to 275 MPa, an ultimate strength up to 310 MPa, a Brinell hardness of 95 HBW, and a fatigue strength of approximately 96.5 MPa, etc. Since the construction material of the AA6061 alloy is lighter than the foregoing ones, therefore the AA6061 can be applied extensively in key components of means of transportation such as bicycles, cars, ships and airplanes. As the ultimate strength, hardness and fatigue resistance are important mechanical properties of a construction material, how to obtain the best mechanical properties of an aluminum-magnesium silicon alloy in whatever condition is a subject worth researching. For instance, a high strength Al—Mg—Si alloy as disclosed in U.S. Pat. No. 5,571,347 achieves the effect of increasing the ultimate strength and the yield strength of an alloy material up to 434 MPa and 379 MPa respectively by changing the composition of the material, adding more magnesium (Mg) and silicon (Si) elements in melting aluminum ingots, and producing solid solution and aging strengthening effects by T6 heat treatment. Since beryllium (Be) and its compound have a relatively greater toxicity and a relatively higher risk in melting, therefore the present invention eliminates the addition of beryllium (Be). Further, an aluminum alloy having improved damage tolerant characteristics as disclosed in U.S. Pat. No. 5,888,320 achieves the effect of increasing the ultimate strength and the yield strength of an alloy material up to 403 MPa and 367 MPa respectively by changing the composition of the material, adding more copper element (such as 0.88 wt %) when melting an aluminum alloy, and producing solid solution and aging strengthening effects by T6 heat treatment.

SUMMARY OF THE INVENTION

Therefore, it is a primary objective of the present invention to provide a high-strength aluminum-magnesium silicon alloy with better strength, hardness and fatigue resistance than the present existing aluminum-magnesium silicon alloys and to further provide a manufacturing process of the high-strength aluminum-magnesium silicon alloy.

To achieve the aforementioned objective, the present invention improves the mechanical properties including the strength, hardness and fatigue resistance of an aluminum-magnesium silicon alloy by adjusting the composition of an alloy material, and setting the heat treatment parameters. In the aspect of adjusting the composition, trace elements such as vanadium (V) and zirconium (Zr) are added into the aluminum-magnesium silicon alloy to perform a grain refinement of the material in order to improve the strength of an alloy product of the present invention. In the composition of the alloy material of the present invention, the trace elements including 0.4˜1.2 wt. % silicon (Si), less than 0.7 wt. % iron (Fe), 0.2˜1.0 wt. % copper (Cu), less than 0.2 wt. % manganese (Mn), 0.6˜1.6 wt. % magnesium (Mg), less than 0.2 wt. % zinc (Zn), less than 0.10 wt. % titanium (Ti), 0.05˜0.3 wt. % chromium (Cr), 0.1˜0.5 wt. % vanadium (V), 0.1˜0.5 wt. % zirconium (Zr) and less than 0.15 wt. % of impurity are added into the main material aluminum (Al).

The alloy heat treatment of the present invention comprises the following steps: (a) Solution treatment step, wherein a finished good is put into a solution furnace heated to a temperature of 530˜580° C. and held at the temperature for 1˜3 hours; (b) Quenching treatment step, wherein the finished good processed by the solution treatment is immersed into a quenching liquid of 50˜70° C. for a quenching treatment time of 15˜45 minutes; and (c) Aging treatment step, wherein the produced processed by the quenching treatment is put into an aging furnace and heated to 160˜180° C. and held at the temperature for 14˜18 hours.

After the aforementioned three steps are completed, the finished good is cooled by air to form an alloy product with a better strength.

In addition, the following steps of the present invention can also be used to obtain the alloy product of the invention: (a) Alloy composition adjusting step as described above; (b) Material casting step, wherein the foregoing molten alloy composition is casted and molded into a material; (c) Material preheating step, wherein the material is preheated before forging, and the material is put into a preheating furnace heated to a temperature over 500° C. and held at that temperature for at least two hours; (d) Forging molding step, wherein a mold is heated to 200˜400° C., and the operating temperature for forging is set within a range of 250˜500° C., and the material is forged to form a product; and (e) Heat treatment step as described above, wherein the product is processed by a solution treatment, a quenching treatment and an aging treatment sequentially, and finally air cooled to form an alloy product of the present invention.

In summation, the present invention adopting the aforementioned technical measures has the following advantages and effects:

The present invention adds the trace elements including vanadium (V) and zirconium (Zr) into an aluminum-magnesium silicon alloy to refine the grains of the material to a diameter from 50 μm to 100 μm and thus reducing the grain size by 20% over the grain size of the AA6061 cast ingot to improve the mechanical properties of the subsequent alloy product.

The material of the present invention is hot forged and molded, and then a solution heat treatment is performed to melt magnesium (Mg) and silicon (Si) atoms into an aluminum (Al) base to result in a lattice deformation and achieve a strengthening effect, and then an aging heat treatment is performed to precipitate (Mg₂Si) from grains in a precipitated phase, and the precipitated particles act as obstacles to dislocation movement, so that the alloy product of the present invention has a yield strength up to 400 MPa, an ultimate strength up to 505 MPa, a Brinell hardness of 127.3 HBW and a fatigue strength of 155 MPa. Compared with the AA6061-T6, the present invention increases the yield strength of the alloy product by 31%, the ultimate strength by 39%, the hardness by 34%, and the fatigue strength by 55.4%, so that the alloy product of the invention can be used in components with a high structural strength requirement, such as aluminum bicycle frames and frame tubes, aluminum alloy wheels, control arms of a car suspension system as well as alloy products of the transportation means industry, mechanical tool industry, national defense and weapon industry, aerospace industry, 3C electronic industry, and sports and leisure goods industry.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 is a flow chart of manufacturing a high-strength aluminum-magnesium silicon alloy of the present invention;

FIG. 2 is a list of trace elements contained in a material of the present invention;

FIG. 3 is the microstructure of the center of a material of the present invention;

FIG. 4 is the microstructure of the edge of a material of the present invention;

FIG. 5 is a list showing the values of yield strength, ultimate strength and elongation of a material of the present invention;

FIG. 6 is a list showing the value of Brinell hardness of a material of the present invention;

FIG. 7 is a flow chart of a heat treatment step of an alloy product of the present invention;

FIG. 8 is a list showing the values of yield strength, ultimate strength and elongation of an alloy product of the present invention;

FIG. 9 is a list showing the value of Brinell hardness of an alloy product of the present invention;

FIG. 10 is a list of trace element contents of a conventional AA6061 alloy;

FIG. 11 is a list of mechanical properties of a conventional AA6061 alloy processed by heat treatment; and

FIG. 12 is the microstructure of an AA6061 material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The technical characteristics, contents, advantages and effects of the present invention will be apparent with the detailed description of a preferred embodiment accompanied with related drawings as follows.

With reference to FIGS. 1 and 3 for a high-strength aluminum-magnesium silicon alloy and its manufacturing process in accordance with the present invention, the manufacturing process comprises the following steps: (a) an alloy composition adjusting step; (b) a material casting step; (c) a material preheating step; (d) a hot forging step; and (e) a heat treatment step.

In the alloy composition adjusting step (a) as shown in FIGS. 3 and 4, the microstructure show whether there are too many cast holes, cracks and defects, and a better composition is chosen to satisfy the required mechanical properties of an aluminum-magnesium silicon alloy and enhance the fatigue resistance effectively. In FIG. 2, the content of trace elements is adjusted and the traced elements are melted into a main material aluminum (Al).

The silicon (Si) content is 0.4˜1.2 wt. % and used for improving the flowing capability of the molten aluminum (Al), the hot-cracking resistance, the specific gravity and thermal expansion coefficient, and obtaining a solid solution strengthening effect in the subsequent heat treatment step of the present invention.

The iron (Fe) content is less than 0.7 wt. % and used for improving the hot-cracking resistance of the alloy, and achieving a grain refinement of the material of the present invention.

The copper (Cu) content is 0.2˜1.0 wt. % and used for improving the strength and hardness of the alloy significantly, but reducing the hot-cracking resistance), and obtaining a precipitation strengthening effect in the subsequent heat treatment step of the present invention.

The manganese (Mn) content is less than 0.2 wt. % and controlled to a lower content in the alloy for improving the tenacity of the alloy, and obtaining the solid solution strengthening effect and the precipitation strengthening effect in the subsequent heat treatment step of the present invention.

The magnesium (Mg) content is 0.6˜1.6 wt. % and used for improving the strength and hardness of the alloy processed by heat treatment, and setting Mg₂Si mainly in a precipitated phase, and obtaining the precipitation strengthening effect in the subsequent heat treatment step of the present invention.

The zinc (Zn) content is less than 0.2 wt. % and used for reducing oxidation in the alloy and obtaining the precipitation strengthening effect in the subsequent heat treatment step of the present invention.

The titanium (Ti) content is less than 0.10 wt. % and used for a grain refinement of the material of the present invention.

The chromium (Cr) content is 0.05˜0.3 wt. % and used for forming an intermetallic compound such as (CrFe)A₁₇ and (CrMn)Al₁₂ in aluminum, obstructing the heat treatment and hot forging re-crystallization nucleation and growth processes to achieve a strengthening effect to a certain extent and also improve the tenancy of the alloy and lower the sensitivity to stress, corrosion, and cracking, but improve the sensitivity of the quenching treatment, and obtaining a solid solution strengthening effect in the subsequent heat treatment step of the present invention.

The vanadium (V) content is 0.1˜0.5 wt. % and capable of achieving the grain refinement effect of the material of the present invention, and obtaining the precipitation strengthening effect in the subsequent heat treatment step of the present invention.

The zirconium (Zr) content is 0.1˜0.5 wt. % and capable of achieving the grain refinement effect of the material of the present invention, and obtaining the precipitation strengthening effect in the subsequent heat treatment step of the present invention.

In the material casting step (b), the main material aluminum (Al) and the aforementioned trace elements are melted together by a high temperature into a molten state, and then degassed and slagged off, and then casted into ingots, rods sheets, materials with a predetermined cross-sectional shape, or materials with any shape to facilitate upstream manufactures to transport products to downstream forging manufactures. Due to the change of trace elements contained in the material, particularly those containing vanadium (V) and zirconium (Zr) elements, the grains can be refined to have a diameter from 50 μm to 100 μm . With reference to FIGS. 3 and 4 for microstructure of the material of the present invention, the grain refinement helps improving the strength, hardness and fatigue resistance of the subsequent alloy product of the present invention. With reference to FIGS. 5 and 6, six samples of the material of the present invention are collected for testing, and test results show that the material has an average yield strength of 133.66 MPa, an ultimate strength of 176.38 MPa, an elongation of 13.26 EL %, and an average Brinell hardness of 54.9 HBW.

In the forging preheating step (c), the aforementioned ingots, rods, sheets or material with a predetermined cross-sectional shape are preferred. For example, the manufacture of a forged wheel requires manufacturers to put the material into a preheating furnace at a temperature of 300˜500° C. and that temperature is held for 120˜180 minutes.

In the hot forging step (d), parameters for the hot forging manufacture of the material of the present invention are set. For example, the mold of a forged wheel is heated to 200˜400° C., and the operating temperature for the forging process is set within a range of 350˜450° C., and the forging pressurization time is set to 3 seconds, and the forging pressure is set to 55000 KN.

The material is forged into an alloy product of a predetermined shape, so that the hot forging step performs a plastic processing of the material to improve the grain structure of the material, and the material of the alloy product is reformed and homogenized. In addition, a mechanical fibrosis state caused by the continuous grain flow results in better mechanical properties including the fatigue resistance, tenacity, and impact resistance of the alloy product.

In the heat treatment step (e) as shown in FIG. 7, the aforementioned alloy product is put into a solution furnace and heated to a temperature of 530˜580° C., and that temperature is held for 1˜3 hours, and then the alloy product processed by the solution treatment is immersed completely into warm water of 50˜70° C., and the quenching treatment time is 15˜45 minutes, and then quenched alloy product is put into an aging furnace and heated to a temperature of 160˜180° C., and that temperature is held for 14˜18 hours, Finally, the alloy product is air cooled to form the alloy product of the present invention. In the step (e), a solution treatment of the alloy product of the present invention is performed to melt magnesium (Mg) and silicon (Si) atoms into an aluminum (Al) base to cause a lattice deformation and achieve a strengthening effect, and then an aging heat treatment is performed to precipitate (Mg₂Si) from grains in a precipitated phase, and the precipitated particles act as obstacles to dislocation movement, so as to enhance the strength of the alloy product of the present invention.

With reference to FIGS. 8 and 9, several samples of the alloy product produced according to the aforementioned manufacturing process of the present invention are collected for testing, and test results show that the alloy product has an average yield strength of 400.33 MPa, an ultimate strength of 504.87 MPa, an elongation of 7.67 EL %, and an average Brinell hardness of 127.3 HBW. Compared with the general AA6061 material, the material of the present invention has much higher strength, hardness and fatigue resistance.

It is noteworthy that the alloy product of the present invention can be casted as a whole by a single production unit. In other words, the composition of the alloy material of the present invention is casted into a material first, and then processed with a coherent operation of the aforementioned hot forging process and the heat treatment process to produce the alloy product of the present invention, or two production units such as a casting factory and a forging factory located with a far distance apart can cooperate with each other. The casting factor casts the material into an easily transported material such as an ingot, a sheets, a rod, or a material with a predetermined cross-sectional shape according to Steps (a) and (b) of the manufacturing process of the present invention, and then delivers the material to the forging factory. The forging factory refers to Steps (c), (d) and (e) of the manufacturing process of the present invention to manufacture the alloy product of the present invention.

In summation of the description above, the high-strength aluminum-magnesium silicon alloy and its manufacturing process in accordance with the present invention adds vanadium (V) and zirconium (Zr) into an aluminum-magnesium silicon alloy to achieve the grain refinement effect of the alloy and applies the solution heat treatment to melt magnesium (Mg) and silicon (Si) atoms into an aluminum (Al) base to cause a lattice distortion and achieve a strengthening effect and precipitate Mg₂Si from the grains of the alloy, and the precipitated particles act as obstacles to dislocation movement. The alloy product of the present invention has a yield strength up to 400 MPa, an ultimate strength up to 505 MPa, a Brinell hardness 127.3 of HBW, and a fatigue strength of 155 MPa, and thus the alloy product of the present invention can be used in components with a high structural strength requirement, such as aluminum bicycle frames and frame tubes, aluminum alloy wheels, control arms of a car suspension system as well as alloy products of the transportation means industry, mechanical tool industry, national defense and weapon industry, aerospace industry, 3C electronic industry, and sports and leisure goods industry.

The composition of trace elements and the manufacturing process of producing alloys with improved strength in accordance with the present invention comply with the patent application requirements, and thus the invention is duly filed for patent application. While the invention has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.

Claims

1. A high-strength aluminum-magnesium silicon alloy, with a trace element composition comprising: 0.4˜1.2 wt. % silicon (Si), less than 0.7 wt. % iron (Fe), 0.2˜1.0 wt. % copper (Cu), less than 0.2 wt. % manganese (Mn), 0.6˜1.6 wt. % magnesium (Mg), less than 0.2 wt. % zinc (Zn), less than 0.10 wt. % titanium (Ti), 0.05˜0.3 wt. % chromium (Cr), 0.1˜0.5 wt. % vanadium (V), 0.1˜0.5 wt. % zirconium (Zr) and less than 0.15 wt. % impurity which are melted with aluminum (Al) to produce a material.

2. The high-strength aluminum-magnesium silicon alloy of claim 1, wherein grains of the high-strength aluminum-magnesium silicon alloy are refined to a diameter from 50 μm to 100 μm to improve mechanical properties of a subsequent alloy product.

3. A high-strength aluminum-magnesium silicon alloy manufacturing process, comprising the steps of:

4. The high-strength aluminum-magnesium silicon alloy manufacturing process of claim 3, wherein the heat treatment step is to put the alloy product in a solution furnace heated to 530˜580° C. and maintaining the temperature for 1˜3 hours, and then submerge the alloy product completely into a quenching liquid of 50˜70° C., and after a quenching treatment time of 15˜45 minutes, the quenched alloy product is put into an aging furnace heated to 160˜180° C. and maintaining the temperature for 14˜18 hours, and then the alloy product is cooled in air to produce the aluminum-magnesium-silicon alloy product.

5. The high-strength aluminum-magnesium silicon alloy manufacturing process of claim 3, wherein the aluminum-magnesium silicon alloy product has a yield strength up to 400 MPa, an ultimate strength up to 505 MPa, a Brinell hardness up to 127.3 HBW and a fatigue strength up to 155 MPa.