FORGING PROCESS FOR AN ALUMINUM ALLOY PART

Abstract

An forging process for an aluminum alloy part. The forging process includes the following steps: S1, heating an aluminum alloy blank to a solid solution temperature in a heating device, where, a heating and heat preservation time is determined according to a wall thickness of the aluminum alloy blank and prolonged by 20 min when the wall thickness of the aluminum alloy blank is increased by 1 mm; S2, conducting underaging heat treatment; S3, conducting heating and heat preservation on the aluminum alloy blank obtained after the underaging heat treatment with a forging die at 100-300° C., and preheating a final forging die; S4, conducting forming by isothermal forging on the aluminum alloy blank obtained after the heating and heat preservation in step S3 at 100-300° C.; and S5, conducting cooling, trimming and machining on a forged part obtained in step S4 to obtain the aluminum alloy part.

Description

TECHNICAL FIELD

The present disclosure belongs to the field of hot working of materials, and specifically relates to a forging process for an aluminum alloy part.

BACKGROUND ART

As a non-ferrous metal material most widely used in the industry, an aluminum alloy is widely used in aerospace, ships vehicles and other machinery manufacturing industries. In the automobile manufacturing industry, the aluminum alloy is usually used to reduce the weight of an automobile structure, and an aluminum alloy forged part that can be strengthened by heat treatment is also widely used in automobile manufacturing. At present, the die forging forming process of aluminum alloys usually involves lots of technological steps. A common die forging forming process of the aluminum alloy generally includes the following steps: heat treatment before forging, forging forming, solid solution treatment and aging treatment. In a production process of a heat-treatable aluminum alloy, by conducting homogenization heat treatment, segregation can be eliminated. By conducting heating before forging, deformation resistance can be reduced, and the plasticity can be improved. By conducting heat treatment after the forging, the strength of a forged part is improved to meet requirements for properties of a product. In an actual production process, when this production method is used, the time cost and the energy consumption cost are high in the heat treatment processes. Therefore, with several times of the heat treatment in a forging process of the aluminum alloy, the time consumption is high, the actual production period is prolonged, and the production cost is increased.

SUMMARY

In view of the problems of long production period and high energy consumption caused by heating several times in a current aluminum alloy forging pressing process, an objective of the present disclosure is to provide a forging process for an aluminum alloy part. By using the process, the production period can be shortened, and the production efficiency can be improved.

In order to achieve the objective above, the present disclosure adopts the following technical solution. A forging process for an aluminum alloy part includes the following steps:

• • S1, heating an aluminum alloy blank to a solid solution temperature in a heating device, where, a heating and heat preservation time is determined according to a wall thickness of the aluminum alloy blank and prolonged by 20 min when the wall thickness of the aluminum alloy blank is increased by 1 mm;
  • S2, conducting underaging heat treatment;
  • S3, conducting heating and heat preservation on the aluminum alloy blank (called a part when the step of pre-forging forming is added) obtained after the underaging heat treatment with a forging die at 100-300° C., and preheating a final forging die;
  • S4, conducting forming by isothermal forging on the aluminum alloy blank (part) obtained after the heating and heat preservation in step S3 at 100-300° C.; and
  • S5, conducting cooling, trimming and machining on a forged part obtained in step S4 to obtain the aluminum alloy part (a final product).

According to the technical solution above, the forging process for an aluminum alloy part further includes conducting pre-forging forming after step S1, where, a die is heated to a forging temperature of 200-500° C., and the aluminum alloy blank is cooled to a pre-forging temperature of 200-450° C. and subjected to the pre-forging forming. Then, the underaging heat treatment is conducted on a pre-forged part.

The aluminum alloy is a 6,000 series aluminum alloy, including an underaged T4 state and a peak-aged T6 state.

In step S1, the heating and heat preservation time is controlled within 90 min.

In step S2, the underaging heat treatment is conducted at a temperature of 100-300° C., and a heat preservation time is controlled within 2-8 h. A specific temperature is determined according to a position of an exothermic peak precipitated in a corresponding GP zone to ensure that after the underaging heat treatment, a precipitated phase only has the GP zone and few β″ phases.

In step S3, a heat preservation temperature and a final forging temperature are determined according to a position of an exothermic peak precipitated in a corresponding β″ zone, the temperature is controlled to ensure that a β′ phase is not further precipitated, and the heat preservation is conducted within 1-10 min.

In step S3, the final forging die is preheated at a temperature of 200° C.

The precipitated phase of the aluminum alloy is a main factor affecting the strength, and the size, type and quantity of the precipitated phase are direct reasons affecting the strength. However, the type, size, quantity and other factors are closely related to a heat treatment process and a forming method of the aluminum alloy. Therefore, the type and quantity of the precipitated phase of the aluminum alloy can be adjusted through deformation at different heat treatment and processing forming stages. At a heat treatment stage before the forming, the precipitated phase with a certain size reaches an underpeak aging stage through appropriate heat treatment. At a subsequent forming stage, the precipitated phase of the aluminum alloy not only has great formability in preheating and forming processes at an appropriate temperature, but also can be prepared into a desired product. In addition, the internal precipitated phase of the aluminum alloy is further evolved to achieve a peak aging effect.

A precipitated strengthening phase of the 6,000 series aluminum alloy is Mg₂Si, which is sequentially changed from the GP zone into the β″ phase, the β′ phase and a β phase. When the temperature is increased, the size of the strengthening phase is gradually increased, the well-coherent β″ phase is substituted with the semi-coherent β′ phase and the incoherent β phase, and as a result, the strength is greatly reduced. Therefore, a large number of the β″ phases that are well coherent with a matrix can be obtained by controlling the type and quantity of the precipitated phase to ensure a precipitation strengthening effect, and a part meeting requirements for strength is obtained.

By using the process of the present disclosure, a deformation process and a heat treatment control process of an aluminum alloy forged part are synergized. The type and quantity of the precipitated phase of the aluminum alloy are adjusted through deformation at different heat treatment and processing forming stages to ensure the precipitation strengthening effect and realize rapid hot forming. The production period can be shortened, the production cost can be reduced, and the production efficiency is improved.

According to the present disclosure, rapid hot forming of the aluminum alloy is realized. Compared with an existing widely used forging process, the present disclosure has the following beneficial effects. Generally, heating before forging, solid solution treatment and artificial aging treatment need to be conducted on a blank before forging forming, and it takes at least ten hours to strengthen the blank by heat treatment. However, when the rapid hot forming is conducted by using the process of the present disclosure, not only is a heat treatment process reduced, but also the artificial aging time is shortened. In general, under the condition of ensuring properties of a material, not only can the period of the entire forging process shortened, but also the energy consumption required for the heat treatment can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a general forging forming process of an existing aluminum alloy.

FIG. 2 is a diagram showing a processing flow of a simple part in Example 1 of the present disclosure (the left half part is a flow diagram, and the right half part is a diagram showing a temperature-time curve).

FIG. 3 is a diagram showing a processing flow of a complex part in Example 2 of the present disclosure.

FIG. 4a is a physical diagram showing a trial-produced control arm in Example 3 of the present disclosure.

FIG. 4b is a diagram showing a sampling area of a tensile sample in Example 3 of the present disclosure.

FIG. 4c is a diagram showing a size of the tensile sample in Example 3 of the present disclosure.

In the figures, P—blank; Stp.1—Conduct heating and heat preservation; Stp.2—Pre-forge; Stp.3—Final forge; Stp.4—Solid solution treatment; Stp.5—Aging treatment; Stp.11—Heat to a solid solution temperature and conduct heat preservation; Stp.21—Forge.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure is further described below with reference to accompanying drawings and examples.

Example 1

For a simple part requiring only die forging once, a forging process for an aluminum alloy part included the following steps (as shown in FIG. 2):

• • S1, an aluminum alloy blank was heated to a solid solution temperature (for solid solution treatment) in a heating device, where, a heating and heat preservation time was determined according to a wall thickness of the aluminum alloy blank and prolonged by 20 min when the wall thickness of the aluminum alloy blank was increased by 1 mm, the aluminum alloy was a 6,000 series aluminum alloy, and the heating and heat preservation time was controlled within 90 min;
  • S2, underaging heat treatment was conducted on the aluminum alloy blank at a temperature of 100-150° C. for 2-8 h;
  • S3, heat preservation was conducted on the aluminum alloy blank obtained after the underaging heat treatment at 200-250° C. for 5-10 min, and a forging die was preheated to 200° C.;
  • S4, final forging forming was conducted by isothermal forging on the aluminum alloy blank obtained after the underaging heat treatment at 100-300° C.; and
  • S5, cooling, trimming and machining were conducted on a forged part to obtain a final product of an aluminum alloy part.

A processing flow in this example was shown in FIG. 2.

A precipitated strengthening phase of the 6,000 series aluminum alloy was Mg₂Si, which was sequentially changed from a GP zone into a β″ phase, a β′ phase and a β phase. When the temperature was increased, the size of the strengthening phase was gradually increased, the well-coherent β″ phase was substituted with the semi-coherent β′ phase and the incoherent R phase, and as a result, the strength was greatly reduced. A supersaturated solid solution was formed by the solid solution treatment. By controlling the temperature and time of the underaging heat treatment, the GP zone was converted into about 70%-80% of the β″ phase. Finally, by controlling the temperature and time of final forging, the remaining GP zone was further converted into about 95% of the β″ phase. The generation of the β′ phase and the β phase with a low precipitation strengthening effect was avoided, the purpose of ensuring the precipitation strengthening effect was achieved, and thus, properties of a material were ensured.

Example 2

For a complex part requiring die forging several times, an forging process for an aluminum alloy part included the following steps (as shown in FIG. 3):

• • S1, solid solution treatment was conducted on an aluminum alloy blank in a heating device, where, a heating and heat preservation time was determined according to a wall thickness of the aluminum alloy blank and prolonged by 20 min when the wall thickness of the aluminum alloy blank was increased by 1 mm, and the aluminum alloy was a 6,000 series aluminum alloy;
  • S2, a die was heated to a forging temperature, and the aluminum alloy blank obtained after the solid solution treatment was cooled to a pre-forging temperature of 450° C. and subjected to pre-forging forming;
  • S3, underaging heat treatment was conducted on a part obtained after the pre-forging forming at a temperature of 100-150° C. for 2-8 h;
  • S4, heat preservation was conducted on the part obtained after the underaging heat treatment at 200-250° C. for 5-10 min, and a final forging die was preheated to 200° C.;
  • S5, final forging forming was conducted by isothermal forging on the part obtained after the underaging heat treatment; and
  • S6, cooling, trimming and machining were conducted on a forged part to obtain the aluminum alloy part (a final product).

Where, the time of transferring the forged part between dies during several times of the die forging needed to be as short as possible to avoid the situation that when the transfer time was too long, the temperature was reduced too fast, and the mechanical property of the part was affected.

A processing flow in this example was shown in FIG. 3.

By analyzing a DSC curve of a sample based on the solid solution treatment and the underaging heat treatment, it could be seen that after the underaging heat treatment, a precipitated peak in a GP zone in a solid solution state disappeared, indicating that the GP zone was formed in a supersaturated solid solution state and partially converted into a β″ phase. When the aging time was longer, the conversion amount was larger. In addition, at an appropriate temperature, when the aging time was longer, the quantity of the β″ phase was increased. When a large number of the GP zones and few β″ phases were generated during the aging treatment, a sample formed after heat preservation at 200-250° C. for a certain period of time had high hardness. Besides, the hardness of the formed sample was greatly affected by a forming temperature. When the temperature was high, a precipitated phase was converted into a β′ phase with a low strengthening effect.

According to lots of experimental results, it could be seen that by using this method sequentially including the underaging heat treatment, the heat preservation at an appropriate temperature and the forming, great formability could be achieved, the mechanical property of the sample formed by compression was great, and an evolution process of the precipitated phase could be optimally controlled. Compared with a traditional method of adjusting properties by sequentially conducting forming and heat treatment, the method had higher efficiency and lower energy loss.

Example 3

When a 6,082 aluminum alloy was used as an aluminum alloy blank material, an forging process for an aluminum alloy part specifically included the following steps and parameters:

• • S1, solid solution treatment was conducted on the aluminum alloy blank at 535° C. in a heating device, where, a heating and heat preservation time was determined according to a wall thickness of the aluminum alloy blank and prolonged by 20 min when the wall thickness of the aluminum alloy blank was increased by 1 mm;
  • S2, pre-forging forming was conducted on the aluminum alloy blank obtained after the solid solution treatment at 450° C.;
  • S3, underaging heat treatment was conducted on a part obtained after the pre-forging forming at a temperature of 120±5° C. for 4-6 h;
  • S4, heat preservation was conducted on the part obtained after the underaging heat treatment at 200±5° C. for 5-10 min, and a final forging die was preheated to 200° C.;
  • S5, final forging forming was conducted by isothermal forging on the part obtained after the underaging heat treatment at 100-300° C.; and
  • S6, cooling, trimming and machining were conducted on a forged part to obtain the aluminum alloy part (a final product).

A trial-produced sample (as shown in FIG. 4a, FIG. 4 and FIG. 4c) of an automobile control arm was obtained according to Example 3. A room-temperature tensile test and a hardness test were carried out on the forged part. The room-temperature tensile test was completed in a metal room-temperature tensile machine and carried out three times to obtain an average value. The sample had a tensile strength of 335 MPa and a yield strength of 305 MPa. In addition, a surface of the sample was polished and smoothed to test the hardness. It was tested that the sample had a hardness of 120 HV. According to the tensile test and the hardness, it was shown that a trial-produced control arm had great mechanical property, and requirements for properties of a product were met. Results were shown in the following Table 1.

TABLE 1
Mechanical property requirements and measurement results
		Tensile	Yield
		strength	strength
	Test item	Rm	Rp	Hardness
	Technical requirements	≥330 MPa	≥290 MPa	≥100 HV
	Measurement results	335 MPa	305 MPa	120 HV

According to Table 1, it was indicated that by using the process of the present disclosure, properties of a material could be ensured.

It should be understood that those of ordinary skill in the art can make improvements or transformations based on the above description, and all these improvements and transformations should fall within the protection scope of the appended claims of the present disclosure.

Claims

1. A forging process for an aluminum alloy part, comprising the following steps:

S1, heating an aluminum alloy blank to a solid solution temperature in a heating device, wherein, a heating and heat preservation time is determined according to a wall thickness of the aluminum alloy blank and prolonged by 20 min when the wall thickness of the aluminum alloy blank is increased by 1 mm;

S2, conducting pre-forging forming after step S1, wherein, a pre-forging die is heated to a forging temperature, and the aluminum alloy blank is cooled to a pre-forging temperature of 200-450° C. and subjected to the pre-forging forming;

S3, conducting underaging heat treatment at a temperature of 100-300° C., wherein, a heat preservation time is controlled within 2-8 h, and a specific temperature is determined according to a position of an exothermic peak precipitated in a corresponding GP zone to ensure that after the underaging heat treatment, a precipitated phase only has the GP zone and few β″ phases;

S4, conducting heating and heat preservation on the aluminum alloy blank obtained after the underaging heat treatment at 100-300° C., and preheating a final forging die;

wherein, a heat preservation temperature and a final forging temperature are determined according to a position of an exothermic peak precipitated in a corresponding β″ zone, the temperature is controlled to ensure that a β′ phase is not further precipitated, and the heat preservation is conducted within 1-10 min;

S5, conducting final forging forming by isothermal forging on the aluminum alloy blank obtained after the heating and heat preservation in step S4 at 100-300° C.; and

S6, conducting cooling, trimming and machining on a forged part obtained in step S5 to obtain the aluminum alloy part.

2. The forging process of claim 1, wherein, the aluminum alloy is a 6,000 series aluminum alloy.

3. The forging process of claim 1, wherein, in step S4, the final forging die is preheated at a temperature of 200° C.