METHOD FOR FORMING AN ALUMINUM ALLOY SHEET PART

Abstract

 Disclosed is a method for moulding an aluminium alloy sheet part, comprising: i) heating an aluminium alloy sheet material to a solid solution temperature window range for solid solution treatment; ii) transferring the solid solution-treated aluminium alloy sheet material into a mould; iii) closing the mould, and moulding with the mould being closed for 0.5 s or more; and iv) cooling the mould to cool a moulded part. The moulding method is particularly suitable for moulding parts with complex shapes and does not need continuous annealing treatment, thereby quite reducing the material cost. Moreover, the moldability of the material at a high temperature is multiplied, the resilient modulus is low, the number of subsequent part moulding processes is reduced, and the loss of raw materials is reduced.

Description

Technical Field

[0001] The invention belongs to the field of metal product machining. Particularly, the invention relates to a method for moulding an aluminium alloy sheet part.

Background Art

[0002] Aluminium alloys have been widely applied because of high performance-to-weight ratio, advantageous corrosion resistance and other factors. Some aluminium alloys are usually used for applications in which they are used at the normal temperature, generally, -10 - 40°C.

[0003] Aluminium alloys having been applied to the vehicle industry mainly include 2xxx(Al-Cu-Mg), 5xxx(Al-Mg), 6xxx(Al-Mg-Si) and 7xxx(Al-Zn-Mg-Cu) series. The aluminium alloy of the 5xxx series has an excellent moldability. The aluminium alloy of the 2xxx series, which can be subjected to heat treatment for reinforcement, has a high strength and a good weldability and forgeability. The aluminium alloy of the 6xxx series has both a good moldability in the T4/T4P state and a high paint-baking age-hardening response capability (increment of alloy yield strength before and after paint baking). The aluminium alloy of the 7xxx series has a good strength and toughness.

[0004] Aluminium alloy stamping forming materials for vehicles are mostly age-hardening aluminium alloy materials. Generally, after the material is rolled to the desired thickness (F state), continuous annealing is performed in an aluminium factory to reach the T4 state, and then, cold stamping deformation is performed. If any one of processes is not controlled appropriately, many problems will be caused, including the continuous annealing quality control problem, the material resilience problem in the stamping process, low moulding, etc. Hot pressing can improve the moldability and reduce the resilience, but it destroys the desired micro-structure. Therefore, the micro-structure needs to be subjected to solid solution heat treatment for recovery after moulding, which causes a moulded part to be deformed during quenching after the solid solution heat treatment.

[0005] To overcome the defects, various efforts have been made, and some new technologies have been developed. In WO 2008/059242, a moulding method is disclosed, comprising solid solution heat treatment, moulding and cold-mould quenching. In the method, an aluminium alloy blank is subjected to solid solution heat treatment and quickly transferred into a set of cold moulds, and the cold moulds are immediately closed so as to form a moulded component. The moulded component is held in the cold moulds during cooling of the moulded component.

[0006] In EP 2324137, a moulding method is disclosed, which relates to very fast mould closing. However, traditional presses cannot achieve such high-speed mould closing, and it is necessary to manufacture special tools or perform great upgrading, thereby remarkably increasing the setup cost. In the method described in EP 2324137, hot pressing may need a stamping-stroke speed higher than 100 mm/s, and in order to obtain a member having the optimum performance, a stamping speed which is 400 mm/s or higher may be required. The traditional presses are usually operated at a much lower speed and usually have the highest power stroke speed lower than 50 mm/s.

[0007] Therefore, it is still necessary to rationally design a moulding machining technology for aluminium alloy products based on traditional devices.

Summary of the Invention

[0008] An object of the invention is to use an existing device to obtain an aluminium alloy product having desired properties, especially mechanical properties, through machining.

[0009] According to one aspect of the invention, a method for moulding an aluminium alloy sheet part is provided, comprising the following steps:

i) heating an aluminium alloy sheet material to a solid solution temperature window range for solid solution treatment;

ii) transferring the solid solution-treated aluminium alloy sheet material into a mould;

iii) closing the mould to form a part, and moulding with the mould being closed for 0.5 s or more; and

iv) cooling the mould to cool the moulded part.

[0010] According to another aspect of the invention, an aluminium alloy sheet part is provided, which is prepared by the above moulding method.

[0011] According to still another aspect of the invention, a vehicle component is provided, which is prepared by the above moulding method.

[0012] According to yet another aspect of the invention, a vehicle is provided, comprising the above aluminium alloy sheet part or the above vehicle component.

[0013] The method for moulding an aluminium alloy sheet part of the invention is especially suitable for moulding parts with complex shapes, only needs a sheet material in an F state and does not need continuous annealing treatment, thereby quite reducing the material cost. Moreover, the moldability of the material at a high temperature is multiplied, the resilient modulus is low, the number of subsequent part moulding processes is reduced, and the loss of raw materials is reduced. In addition, by using the method for moulding an aluminium alloy sheet part of the invention, the existing device does not need to be modified.

[0014] The method for moulding an aluminium alloy sheet part of the invention is combined with the capacity of the existing equipment and the production capacity, and can obtain better material properties while ensuring mass production.

Brief Description of the Drawing

[0015] The invention is described in conjunction with the accompany drawing such that those skilled in the art can better understand various features and advantages of the invention.

[0016] Fig. 1 is a schematic diagram of a temperature-time curve of a method for moulding an aluminium alloy sheet part of the invention.

Detailed Description of Embodiments

[0017] A technical solution of the invention is described in detail below.

[0018] According to one aspect of the invention, a method for moulding an aluminium alloy sheet part is provided, comprising the following steps:

i) heating an aluminium alloy sheet material to a solid solution temperature window range for solid solution treatment;

ii) transferring the solid solution-treated aluminium alloy sheet material into a mould;

iii) closing the mould to form a part, and moulding with the mould being closed for 0.5 s or more; and

iv) cooling the mould to cool the moulded part.

[0019] There may be differences between solid solution temperature windows of different aluminium alloy materials. Those skilled in the art can determine a solid solution temperature window according to the aluminium alloy sheet material used.

[0020] The thickness of the aluminium alloy sheet material may be any appropriate thickness, e.g. 0.7-3.0 mm.

[0021] The solid solution temperature window refers to temperatures for performing solid solution treatment. Solid solution treatment needs to dissolve alloy elements of the aluminium alloy material in an aluminium substrate as much as possible. Those skilled in the art can determine the solid solution temperature window according to the aluminium alloy used and the time for the aluminium alloy material to be maintained within the solid solution temperature window.

[0022] In some embodiments, the solid solution temperature window is 400-600°C, more preferably 450-600°C, and most preferably 450-550°C.

[0023] In some embodiments, the time for the aluminium alloy sheet material to be maintained within the solid solution temperature window range to complete the solid solution treatment is generally shorter than 30 mins, e.g. 2-25 mins, and preferably 3-15 mins.

[0024] In some embodiments, the time for transferring the aluminium alloy sheet material from a heating device to a mould is longer than 5 s, e.g. 3-35 s, and preferably 5-30 s, e.g. 10 s.

[0025] Preferably, the solid solution-treated aluminium alloy sheet material starts to be moulded after leaving the heating device within 20 s.

[0026] In some embodiments, the moulding time with the mould being closed is 0.5-10 s, for example, may be 0.5-7 s, 0.5-5 s, or 0.5-3 s, and may also be 3-7 s or 3-5 s.

[0027] The moulding time with the mould being closed is also known as mould closing time, that is, the time from when the aluminium alloy sheet material is completely transferred into the mould to when the mould is completely closed.

[0028] The time for holding the moulded part in the mould may be determined according to the thickness of the moulded part.

[0029] In some embodiments, the time for holding the moulded part in the mould is longer than 5 s, e.g. 3-25 s, and preferably 5-20 s, e.g. 10 s.

[0030] In some embodiments, the moulded part is cooled to 120°C or below, e.g. 80°C or below.

[0031] In some embodiments, the moulded part is cooled to 120°C or below, e.g. 80°C or below within more than 5 s, e.g. within 5-20 s.

[0032] In some embodiments, the temperature of the mould is kept at 120°C or below, e.g. 80°C or below, or at the room temperature.

[0033] For example, a built-in cooling water channel may be used to cool the mould, so as to achieve the effect of cooling the moulded part.

[0034] The aluminium alloy sheet material in the method of the invention may be any aluminium alloy material usually used for vehicle part machining, such as an aluminium alloy material selected from the 2xxx, 5xxx, 6xxx and 7xxx series, for example, AA7075.

[0035] The aluminium alloy sheet material may be subjected to or not subjected to age-hardening treatment in advance.

[0036] The moulded part may be subjected to aging treatment well-known by those skilled in the art: the moulded part is heated to an artificial hardening temperature, and this temperature is kept until precipitation hardening is allowed. The typical temperature is 100-250°C. The typical time is 5-40 hours, for example, the temperature is kept at 125°C for 24 hours.

[0037] The method for moulding an aluminium alloy sheet part of the invention only needs a sheet material in an F state, and therefore, the raw material purchase cost can be reduced. The method for moulding an aluminium alloy sheet part of the invention is especially suitable for the machining of parts with complex shapes, because after the aluminium alloy material is subjected to solid solution, the moldability is multiplied at the high temperature, and the percentage of elongation exceeds 50%. In the material deforming process, the resilient modulus is low, the moulding dimension stability is good, one-process moulding is achieved, the number of subsequent moulding processes is reduced, and therefore, the technology cost of the moulding method of the invention is low. In addition, in the material deforming process, the moldability is good, blank holding and drawing are not needed, the loss of moulding materials is small, and the material utilization rate is high.

[0038] According to another aspect of the invention, an aluminium alloy sheet part is provided, which is prepared by the above moulding method.

[0039] According to still another aspect of the invention, a vehicle component is provided, which is prepared by the above moulding method.

[0040] The vehicle component may be a structural component, such as a B column inner plate, a B column inner plate reinforcing plate and an A column inner plate, a hinge reinforcing plate, a floor member, etc.

[0041] According to yet another aspect of the invention, a vehicle is provided, comprising the above aluminium alloy sheet part or the above vehicle component.

[0042] In the description and claims of this application, the nomenclature for the aluminium alloy conforms to the latest regulations of the Aluminium Association known in the prior art. Moreover, each alloy in each series has been registered in the Aluminium Association this year. For example, the aluminium alloys in the 2xxx series are called high-strength alloys and generally comprise magnesium and cooper serving as a main alloy element. The alloys in the 6xxx and 7xxx series are also called high-strength alloys and are usually reinforced through heat treatment by depositing main alloy elements thereof, and the main alloy elements are silicon and magnesium as for the 6xxx series and copper, zinc and magnesium as for the 7xxx series.

[0043] In the description and claims of this application, all numbers representing quantity, percentage, part by weight, etc. should be understood as being modified by 'approximate'.

[0044] In the description and claims of this application, the terms "include" and "comprise" cover the case where other elements not explicitly mentioned are also included or comprised, and the case composed of the mentioned elements.

[0045] The concept and the generated technical effects of the invention will be further described below with reference to embodiments such that those skilled in the art can fully understand the purposes, features and effects of the invention. However, the scope of the invention is not limited herein.

Embodiment 1

[0046] According to the dimensions of a mould, a 7075 aluminium alloy sheet which is 2.0 mm thick is cut into a material sheet matching the dimensions of the mould, the material sheet is put into a heating furnace for heating, the solid solution temperature is set to be 480°C, and heat preservation is performed for 5 min. Then, the material sheet is transferred from the heating furnace into the mould kept at the room temperature within 10 s, and 0.5 s later, mould closing is performed for 10 s. The mould is opened to remove the moulded part, and aging treatment is performed at 125°C for 24 hours. Then, the part is sampled, the tensile strength, the yield strength and the percentage of elongation of an obtained sample of the part are tested according to ASTM E8/E8M, and results are listed in Table 1.

Embodiment 2

[0047] According to the dimensions of a mould, a 7075 aluminium alloy sheet which is 2.0 mm thick is cut into a material sheet matching the dimensions of the mould, the material sheet is put into a heating furnace for heating, the solid solution temperature is set to be 480°C, and heat preservation is performed for 5 min. Then, the material sheet is transferred from the heating furnace into the mould kept at the room temperature within 10 s, and 3 s later, mould closing is performed for 10 s. The mould is opened to remove the moulded part, and aging treatment is performed at 125°C for 24 hours. Then, the part is sampled, the tensile strength, the yield strength and the percentage of elongation of an obtained sample of the part are tested according to ASTM E8/E8M, and results are listed in Table 1.

Embodiment 3

[0048] According to the dimensions of a mould, a 7075 aluminium alloy sheet which is 2.0 mm thick is cut into a material sheet matching the dimensions of the mould, the material sheet is put into a heating furnace for heating, the solid solution temperature is set to be 480°C, and heat preservation is performed for 5 min. Then, the material sheet is transferred from the heating furnace into the mould kept at the room temperature within 10 s, and 10 s later, mould closing is performed for 10 s. The mould is opened to remove the moulded part, and aging treatment is performed at 125°C for 24 hours. Then, the part is sampled, the tensile strength, the yield strength and the percentage of elongation of an obtained sample of the part are tested according to ASTM E8/E8M, and results are listed in Table 1.

Table 1. Property comparison of 7075 aluminium alloy sheet at different mould closing times

Embodiment	Mould closing time (S)	Tensile strength (MPa)	Yield strength (MPa)	Percentage of elongation (%)
1	0.5	552	509	12.4
2	3	533	474	9.1
3	10	509	425	8.4

Embodiment 4

[0049] According to the dimensions of a mould, a 7075 aluminium alloy sheet which is 2.0 mm thick is cut into a material sheet matching the dimensions of the mould, the material sheet is put into a heating furnace for heating, the solid solution temperature is set to be 490°C, and heat preservation is performed for 5 min. Then, the material sheet is transferred from the heating furnace into the mould kept at the room temperature within 20 s, and 1 s later, mould closing is performed for 10 s. The mould is opened to remove the moulded part, and aging treatment is performed at 125°C for 24 hours. Then, the part is sampled, the tensile strength, the yield strength and the percentage of elongation of an obtained sample of the part are tested according to ASTM E8/E8M, and results are listed in Table 2.

Embodiment 5

[0050] According to the dimensions of a mould, a 7075 aluminium alloy sheet which is 2.0 mm thick is cut into a material sheet matching the dimensions of the mould, the material sheet is put into a heating furnace for heating, the solid solution temperature is set to be 470°C, and heat preservation is performed for 5 min. Then, the material sheet is transferred from the heating furnace into the mould kept at the room temperature within 20 s, and 1 s later, mould closing is performed for 10 s. The mould is opened to remove the moulded part, and aging treatment is performed at 125°C for 24 hours. Then, the part is sampled, the tensile strength, the yield strength and the percentage of elongation of an obtained sample of the part are tested according to ASTM E8/E8M, and results are listed in Table 2.

Table 2. Property comparison of 7075 aluminium alloy sheet at different solid solution times

Embodiment	Solution time °C	Tensile strength (MPa)	Yield strength (MPa)	Percentage of elongation (%)
4	490	546	505	12.1
5	470	543	487	10.2

Embodiment 6

[0051] According to the dimensions of a mould, a 7075 aluminium alloy sheet which is 2.0 mm thick is cut into a material sheet matching the dimensions of the mould, the material sheet is put into a heating furnace for heating, the solid solution temperature is set to be 480°C, and heat preservation is performed for 5 min. Then, the material sheet is transferred from the heating furnace into the mould kept at the room temperature within 10 s, and 3 s later, mould closing is performed for 10 s. The mould is opened to remove the moulded part, and aging treatment is performed at 125°C for 24 hours. Then, the part is sampled, the tensile strength, the yield strength and the percentage of elongation of an obtained sample of the part are tested according to ASTM E8/E8M, and results are listed in Table 3.

Embodiment 7

[0052] According to the dimensions of a mould, a 7075 aluminium alloy sheet which is 2.0 mm thick is cut into a material sheet matching the dimensions of the mould, the material sheet is put into a heating furnace for heating, the solid solution temperature is set to be 480°C, and heat preservation is performed for 5 min. Then, the material sheet is transferred from the heating furnace into the mould kept at the room temperature within 25 s, and 3 s later, mould closing is performed for 10 s. The mould is opened to remove the moulded part, and aging treatment is performed at 125°C for 24 hours. Then, the part is sampled, the tensile strength, the yield strength and the percentage of elongation of an obtained sample of the part are tested according to ASTM E8/E8M, and results are listed in Table 3.

Table 3. Property comparison of 7075 aluminium alloy sheet at different transferring times

Embodiment	Transferring time s	Tensile strength (MPa)	Yield strength (MPa)	Percentage of elongation (%)
6	10	546	501	12.0
7	25	513	487	10.3

[0053] While some aspects of the invention have been illustrated and discussed, it should be realized by those skilled in the art that the above aspects can be changed without departing from the principle and spirit of the invention. Therefore, the scope of the invention will be defined by the appended claims and equivalents thereof.

Claims

1. A method for moulding an aluminium alloy sheet part, characterized by comprising:

i) heating an aluminium alloy sheet material to a solid solution temperature window range for solid solution treatment;

ii) transferring the solid solution-treated aluminium alloy sheet material into a mould;

iii) closing the mould to form a part, and moulding with the mould being closed for 0.5 s or more; and

iv) cooling the mould to cool the moulded part.

2. The moulding method according to claim 1, characterized in that the solid solution temperature window is 400-600°C, more preferably 450-600°C, and most preferably 450-550°C.

3. The moulding method according to claim 1 or 2, characterized in that the time for the aluminium alloy sheet material to be maintained within the solid solution temperature window range to complete the solid solution treatment is shorter than 30 mins.

4. The moulding method according to any one of claims 1 to 3, characterized in that the time for transferring the aluminium alloy sheet material from a heating spot to the mould is longer than 5 s.

5. The moulding method according to any one of claims 1 to 4, characterized in that the time for holding the moulded part in the mould is longer than 5 s.

6. The moulding method according to any one of claims 1 to 5, characterized in that the moulded part is cooled to 120°C or below, and preferably 80°C or below.

7. The moulding method according to any one of claims 1 to 5, characterized in that the moulded part is cooled to 120°C or below, and preferably 80°C or below within more than 8 s.

8. The moulding method according to any one of claims 1 to 7, characterized in that the aluminium alloy sheet material is an aluminium alloy material selected from 2xxx, 5xxx, 6xxx and 7xxx series.

9. An aluminium alloy sheet part, prepared by a moulding method according to any one of claims 1 to 8.

10. A vehicle component, prepared by a moulding method according to any one of claims 1 to 8.

11. A vehicle, comprising an aluminium alloy sheet part according to claim 9 or a vehicle component according to claim 10.

Drawing