Heat treatment process of 6xxx aluminum alloy and automobile anti-collision beam

Abstract

The invention provides a heat treatment process of a 6xxx aluminum alloy, which comprises the following steps: S1) carrying out solution treatment on a 6xxx aluminum alloy cold-rolled plate to obtain a solution plate; (S2) the solid solution plate is subjected to pre-aging treatment, and a pre-aging plate is obtained; s3) carrying out aging treatment on the pre-aging plate; the furnace gas temperature of the pre-aging treatment is 90-110 DEG C, and coiling is performed after the furnace gas is heated to 70-95 DEG C; and the aging treatment specifically comprises the following steps: heating to 230 DEG C or furnace gas at 270 DEG C at a rate of more than 30 DEG C / h, heating the pre-aging plate to 230 DEG C, preserving heat for 10-12 hours, and cooling. According to the heat treatment process provided by the invention, by limiting specific process parameters and regulating and controlling the size and distribution of the grain boundary and the intragranular phase, the intergranular corrosion resistance of the alloy is improved on the premise of ensuring the strength, the elongation, the strain hardening index and the plastic strain ratio, and the obtained 6xxx aluminum alloy can be applied to front and rear anti-collision beams of automobiles.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloys, and in particular to a heat treatment process for a 6xxx aluminum alloy and an automobile anti-collision beam. Background Art

[0002] With the rapid development of the automobile industry, environmental pollution and resource shortage issues have become increasingly prominent. Saving resources and reducing pollution have become two major issues that the automobile industry needs to solve. Focusing on sustainable development, the tasks of reducing automobile weight, reducing fuel consumption and reducing emission pollution are particularly urgent. Automobile lightweight technology is one of the important ways to solve these problems.

[0003] 6xxx alloy plates are favored by European and American countries due to their high strength. They are mainly used in automobile outer panels. At present, the main focus is on the preparation, processing and stamping performance of 6xxx alloy plates. 6xxx alloys have high strength and great potential for lightweighting in automobile anti-collision beams, but automobile anti-collision beams have certain requirements for the material's strength, elongation, strain hardening index, plastic strain and intergranular corrosion resistance. 6xxx alloys containing Cu elements in their composition have an adverse effect on intergranular corrosion resistance, but there are few studies, especially lacking comprehensive performance considerations of strength, elongation, strain hardening index and plastic strain.

[0004] A Chinese patent with publication number CN114737070A discloses a method for preparing 6xxx-T7 aluminum alloy plates. The patent does not comprehensively consider the alloy strain hardening index n value and plastic strain ratio r value formability indicators; in addition, the patent limits multiple processes such as hot rolling coil thickness and cold rolling passes, requiring coordinated control of multiple processes, complicated operation, and not conducive to production scheduling; the solution quenching treatment is limited to a heating speed of 5°C / s to 520-540°C, and the heating rate is difficult to control accurately; the over-aging heat treatment requires the temperature in the box furnace to be reduced to below 180°C before taking out the coil, which is time-consuming and difficult to control.

[0005] A Chinese patent with publication number CN101885000A discloses a processing method for improving the stamping formability of 6xxx aluminum alloy automotive plates. The patent does not take into account the corrosion resistance of the alloy. In addition, the homogenization heat treatment process in the patent is a multi-temperature stage, and the process is cumbersome. The hot rolling adopts a vertical and horizontal alternating method, and it is difficult to achieve continuous rolling and industrial preparation in an industrialized manner. The solid solution heat treatment is a salt bath, which is difficult to apply industrially.

[0006] Therefore, it is necessary to provide a preparation process for 6xxx aluminum alloy to ensure its strength, elongation, strain hardening index and plastic strain ratio, and to improve the alloy's resistance to intergranular corrosion to meet the application of front and rear anti-collision beams of automobiles. Summary of the invention

[0007] The technical problem solved by the present invention is to provide a heat treatment process for 6xxx aluminum alloy. The heat treatment process provided by the present application improves the intergranular corrosion resistance of the alloy while ensuring the strength, elongation, strain hardening index and plastic strain ratio of the 6xxx aluminum alloy.

[0008] In view of this, the present application provides a heat treatment process for a 6xxx aluminum alloy, comprising the following steps:

[0009] S1) subjecting the 6xxx aluminum alloy cold-rolled sheet to a solution treatment to obtain a solution sheet;

[0010] S2) performing a pre-aging treatment on the solid solution plate to obtain a pre-aging plate;

[0011] S3) subjecting the pre-aging plate to aging treatment;

[0012] The furnace gas temperature of the pre-aging treatment is 90-110°C, and the coiling is carried out after heating to 70-95°C;

[0013] The aging treatment is specifically as follows:

[0014] The pre-aged plate is heated to 230°C at a rate of >30°C / h or at 270°C in furnace gas, and then cooled after being kept at this temperature for 10 to 12 hours.

[0015] Preferably, the solution treatment is carried out by heating the temperature in an air cushion furnace to 550-565° C., keeping the temperature for 15-60 seconds and then quenching with water.

[0016] Preferably, the solution treatment further includes straightening, and the straightening is 0.3-1.5%.

[0017] Preferably, the coiling is followed by keeping warm for 4 to 8 hours or naturally cooling to room temperature.

[0018] Preferably, the cooling is performed by air cooling to room temperature at a rate of >10°C / h.

[0019] Preferably, in the pre-aging treatment, the furnace gas temperature is 95-105°C, and the heating temperature is 75-90°C.

[0020] Preferably, during the aging treatment, the heating rate is 35-45° C. / h.

[0021] Preferably, the cooling rate is 15-20°C / h.

[0022] Preferably, the 6xxx aluminum alloy comprises, by mass percentage, 0.3-1.8% Si, 0-0.4% Fe, 0.1-0.9% Cu, 0.1-0.45% Mn, 0.1-1.4% Mg, 0-0.3% Cr, 0-0.1% Ti, and the balance is Al.

[0023] The present application also provides an automobile anti-collision beam, which is prepared from a 6xxx aluminum alloy sheet obtained by the heat treatment process.

[0024] The present application provides a heat treatment process for a 6xxx aluminum alloy, which firstly performs a solution treatment on a 6xxx aluminum alloy cold-rolled plate to obtain a solution plate; then performs a pre-aging treatment on the solution plate to obtain a pre-aging plate; and finally performs an aging treatment on the pre-aging plate to obtain a 6xxx aluminum alloy plate; in the above-mentioned heat treatment process, the present application regulates the grain boundaries, the size and distribution of the intragranular phases of the 6xxx aluminum alloy by limiting the process means of the pre-aging treatment and the aging treatment, so that the intergranular corrosion resistance of the heat-treated 6xxx aluminum alloy is improved while ensuring the strength, elongation, strain hardening index and plastic strain ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a photo of intergranular corrosion of the 6xxx alloy plate prepared in Example 1 of the present invention;

[0026] Figure 2 This is a photo of intergranular corrosion of the 6xxx alloy plate prepared in Comparative Example 1 of the present invention;

[0027] Figure 3 This is a transmission photograph of the grain boundary phase of the 6xxx alloy plate prepared in Example 1 of the present invention;

[0028] Figure 4 This is a transmission photograph of the grain boundary phase of the 6xxx alloy plate prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0029] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0030] In view of the performance requirements of 6xxx aluminum alloys used in automobile plates in the prior art and the problem that 6xxx aluminum alloys cannot simultaneously meet the requirements in terms of strength, elongation, strain hardening index, plastic strain ratio and intergranular corrosion resistance, the embodiment of the present invention discloses a heat treatment process for 6xxx aluminum alloys, comprising the following steps:

[0031] S1) subjecting the 6xxx aluminum alloy cold-rolled sheet to a solution treatment to obtain a solution sheet;

[0032] S2) performing a pre-aging treatment on the solid solution plate to obtain a pre-aging plate;

[0033] S3) subjecting the pre-aging plate to aging treatment;

[0034] The furnace gas temperature of the pre-aging treatment is 90-110°C, and the coiling is carried out after heating to 70-95°C;

[0035] The aging treatment is specifically as follows:

[0036] The pre-aged plate is heated to 230°C at a rate of >30°C / h or at 270°C in furnace gas, and then cooled after being kept at this temperature for 10 to 12 hours.

[0037] The present application provides a heat treatment process for a 6xxx aluminum alloy, which firstly performs a solution treatment on a 6xxx aluminum alloy cold-rolled sheet to obtain a solution plate; the preparation of the 6xxx aluminum alloy cold-rolled sheet is prepared according to a method well known to those skilled in the art, and the present application does not impose any particular restrictions on this. The solution treatment is to recrystallize the grain structure of the 6xxx aluminum alloy, and the grain size can be controlled to be 30 to 35 μm, the aspect ratio to be 3.3 to 3.8, and the Mg and Si elements at the grain boundaries and in the grains are partially dissolved back into the aluminum matrix to form a supersaturated solid solution. The solution treatment adopts an air cushion furnace to raise the temperature to 550-565°C, keeps the temperature for 15-60s and then quenches with water; the solution treatment adopts online continuous annealing. In the present application, the solution treatment is carried out in an air cushion furnace; specifically, the temperature of the solution treatment is 552°C-560°C; by way of example, the temperature of the solution treatment described in the present application is 551°C, 553°C, 554°C, 555°C, 556°C, 557°C, 558°C, 559°C, 560°C, 561°C, 562°C, 563°C or 564°C. The holding time is 20 to 45 s; for example, the holding time described in the present application is 16 s, 17 s, 18 s, 19 s, 21 s, 22 s, 23 s, 24 s, 25 s, 26 s, 27 s, 28 s, 29 s, 30 s, 31 s, 32 s, 33 s, 34 s, 35 s, 36 s, 37 s, 38 s, 39 s, 40 s, 41 s, 42 s, 43 s, 44 s, 45 s, 46 s, 47 s, 48 ​​s, 49 s, 50 s, 51 s, 52 s, 53 s, 54 s, 55 s, 56 s, 57 s, 58 s or 59 s.

[0038] The solution treatment further includes straightening, wherein the straightening is 0.3-1.5%.

[0039] The present application further performs a pre-aging treatment on the solid solution plate, and the pre-aging treatment adopts online continuous annealing; the furnace gas temperature of the pre-aging treatment is 90-110°C, and the plate is coiled after heating to 70-95°C. Further, the plate is kept warm for 4-8 hours or naturally cooled to room temperature after coiling; the pre-aging treatment allows Mg and Si atoms to form clusters in the crystal and fine β" phases to form at the grain boundaries. More specifically, the furnace gas temperature is 95-105°C, and the plate is coiled after 75-92°C; for example, in the present application The temperature of the furnace gas is 91°C, 92°C, 93°C, 94°C, 96°C, 97°C, 98°C, 99°C, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107, 108°C or 109°C; the coiling is performed after the temperature reaches 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C or 84°C. The insulation time is 5h, 6h, 7h or 8h.

[0040] The present application finally performs aging treatment on the pre-aged plate, and the aging treatment adopts online continuous annealing, which heats the pre-aged plate to 230°C at a rate of >30°C / h or heats the pre-aged plate to 230°C at 270°C in furnace gas, keeps the temperature for 10-12h and then cools; further, the cooling is air-cooled to room temperature at a rate of >10°C / h; more specifically, the heating rate is 35-45°C / h, and the cooling rate is 15-20°C / h. The aging treatment is to make the intragranular precipitation phase of the pre-aged plate grow and coarsen, and the grain boundary phase has a length of 100-200nm, a width of 20-30nm, and is discontinuously distributed. .

[0041] In the present application, the 6xxx aluminum alloy includes, by mass percentage, the following: Si: 0.3-1.8%, Fe: 0-0.4%, Cu: 0.1-0.9%, Mn: 0.1-0.45%, Mg: 0.1-1.4%, Cr: 0-0.3%, Ti: 0-0.1%, and the balance is Al.

[0042] The present application also provides an automobile anti-collision beam, which is prepared from the 6xxx aluminum alloy plate obtained by the above-mentioned heat treatment process.

[0043] The heat treatment process of the 6xxx aluminum alloy provided by the present invention can improve the intergranular corrosion resistance of the alloy under the premise of ensuring strength, elongation, strain hardening index and plastic strain ratio by strictly limiting the temperature, time, heating and cooling in the heating, insulation and cooling processes of solid solution, pre-aging and aging treatment; experimental results show that the tensile strength of the prepared 6xxx aluminum alloy plate is 280-300MPa, the yield strength is 230-250MPa, the total elongation at break is ≥10%, the maximum force plastic elongation is ≥6%, and the strain The hardening index n value is ≥0.1, the plastic strain ratio r value is ≥0.75, the maximum intergranular corrosion depth is <250μm, and the average intergranular corrosion depth is <150μm, which can well meet the application requirements of the front and rear anti-collision beams of automobiles; and the present invention does not need to limit the previous processes such as melting, soaking, hot rolling, and cold rolling before heat treatment, and only relies on heat treatment control to achieve the target performance, which is easy to promote; the preparation method provided by the present invention is developed based on industrial equipment, the process has good batch operability, has high production efficiency, and does not increase manufacturing costs.

[0044] In order to further understand the present invention, the heat treatment process of the 6xxx aluminum alloy provided by the present invention is described in detail below in conjunction with the embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0045] Example 1

[0046] S1) subjecting the 6xxx alloy cold-rolled sheet to a solution heat treatment, wherein the solution treatment adopts online continuous annealing, and the 6xxx alloy cold-rolled sheet is heated to 550° C. in an air cushion furnace, kept at this temperature for 60 seconds, water quenched, and straightened by 0.3% to obtain a solution plate;

[0047] S2) performing a pre-aging heat treatment on the solid solution plate, wherein the pre-aging is online continuous annealing, wherein the pre-aging is heating at 90° C. in furnace gas, coiling at 70° C., and naturally cooling to room temperature after coiling to obtain a pre-aged plate;

[0048] S3) performing aging heat treatment on the pre-aged plate, heating the plate to 230°C with furnace gas at 270°C, keeping the temperature for 10 hours, and then cooling the plate to room temperature at a rate of more than 10°C / h to obtain a 6xxx plate.

[0049] Example 2

[0050] S1) subjecting the 6xxx alloy cold-rolled sheet to a solution heat treatment, wherein the solution treatment adopts online continuous annealing, and the 6xxx alloy cold-rolled sheet is heated to 565° C. in an air cushion furnace, kept at this temperature for 15 seconds, water quenched, and straightened by 1.5% to obtain a solution plate;

[0051] S2) performing a pre-aging heat treatment on the solid solution plate, wherein the pre-aging is online continuous annealing, wherein the pre-aging is heating at 110° C. in furnace gas, coiling at 95° C., and naturally cooling to room temperature after coiling to obtain a pre-aged plate;

[0052] S3) performing aging heat treatment on the pre-aged plate, heating the pre-aged plate to 230° C. at 270° C. in furnace gas, keeping the temperature for 12 h, and then cooling the pre-aged plate to room temperature at a rate of more than 10° C. / h to obtain a 6xxx plate.

[0053] Comparative Example 1

[0054] S1) subjecting the 6xxx alloy cold-rolled sheet to a solution heat treatment, wherein the solution treatment adopts online continuous annealing, heating the sheet to 550° C. in an air cushion furnace, holding the sheet for 60 seconds, water quenching, and straightening the sheet by 0.3% to obtain a solution plate;

[0055] S2) performing a pre-aging heat treatment on the solid solution plate, wherein the pre-aging is online continuous annealing, wherein the pre-aging is heating at 90° C. in furnace gas, coiling at 70° C., and naturally cooling to room temperature after coiling to obtain a pre-aged plate;

[0056] S3) performing aging heat treatment on the pre-aged plate, heating the pre-aged plate to 240° C. at 280° C. in furnace gas, keeping the temperature for 14 h, and then cooling the pre-aged plate to room temperature at a rate of more than 10° C. / h to obtain a 6xxx plate.

[0057] Comparative Example 2

[0058] S1) subjecting the 6xxx alloy cold-rolled sheet to a solution heat treatment, wherein the solution treatment is carried out by salt bath annealing to a temperature of 555° C., a holding time of 60 seconds, and water quenching to obtain a solution plate;

[0059] S2) performing a pre-aging heat treatment on the solution-solution plate, wherein the pre-aging is performed by direct heating in a drying oven, wherein the temperature of the drying oven is set at 85° C., and the sample is placed at the temperature, and then naturally cooled to room temperature after being kept at the temperature for 4 hours to obtain a pre-aging plate;

[0060] S3) subjecting the pre-aged plate to aging heat treatment, setting the oven temperature at 230° C., placing the plate at the temperature, keeping the temperature for 12 hours, and then naturally cooling the plate to room temperature to obtain a 6xxx plate.

[0061] The properties of the 6xxx alloy plates prepared in the examples and comparative examples were tested, and the test results are shown in Table 1:

[0062] Table 1 Performance data of 6xxx alloy plates prepared in Examples and Comparative Examples

[0063]

[0064] As shown in Table 1, the performance of the 6xxx alloy plate after the heat treatment process provided by the present application is significantly improved. It can be seen that the process means of solid solution, pre-aging, aging temperature rise, and heat preservation need to be strictly controlled to ensure that the above-mentioned performance meets the use requirements.

[0065] See also Figure 1 , Figure 2 , Figure 1 This is a photo of intergranular corrosion of the 6xxx alloy plate prepared in Example 1. Figure 2 This is a photo of intergranular corrosion of the 6xxx alloy plate prepared in Comparative Example 1. Figure 1 and Figure 2 It can be seen that the intergranular corrosion depth of the 6xxx alloy plate prepared in Example 1 is significantly smaller than that in Comparative Example 1. Considering the tensile strength, yield strength, total elongation at break, maximum force plastic elongation, strain hardening index, and plastic strain ratio r value in Table 1, the 6xxx plate produced by the present invention has good comprehensive performance.

[0066] See also Figure 3 , Figure 4 , Figure 3 This is a transmission photograph of the grain boundary phase of the 6xxx alloy plate prepared in Example 1. Figure 4 This is a transmission photograph of the grain boundary phase of the 6xxx alloy plate prepared in Comparative Example 1; Figure 3 and Figure 4 It can be seen that the grain boundary phase in Example 1 is discontinuous, while the grain boundary phase in Comparative Example 1 is coarsened and continuous. Example 1 uses heat treatment to regulate the grain boundary phase, providing a guarantee for good intergranular corrosion resistance.

[0067] In comparative example 1, the aging temperature is increased and the aging time is increased. Compared with examples 1 and 2 of the present invention, the size of the intragranular phase is coarsened, the strength is significantly reduced, and the yield strength does not reach the target performance; the plastic strain ratio r value is only 0.64, which does not reach the target performance; the grain boundary phase structure grows and is continuous, the intergranular corrosion is serious, and the target performance is not reached.

[0068] Comparative Example 2 did not adopt strict pre-aging, aging heating and cooling control, the intracrystalline strengthening phase did not coarsen and grow, the tensile strength and yield strength did not meet the standards, and the target performance was not achieved; the plastic strain ratio r value was 0.72, which did not achieve the target performance.

[0069] The results of the above Examples 1 to 2 and Comparative Examples 1 to 2 show that the present invention strictly limits the heat treatment temperature and time, regulates the size and distribution of grain boundaries and intragranular phases, and improves the intergranular corrosion resistance of the alloy while ensuring strength, elongation, strain hardening index, and plastic strain ratio. The alloy can be applied to front and rear anti-collision beams of automobiles.

[0070] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0071] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heat treatment process for a 6xxx aluminum alloy, comprising the following steps: S1) subjecting the 6xxx aluminum alloy cold-rolled sheet to a solution treatment to obtain a solution sheet; S2) performing a pre-aging treatment on the solid solution plate to obtain a pre-aging plate; S3) subjecting the pre-aging plate to aging treatment; The furnace gas temperature of the pre-aging treatment is 90-110°C, and the coiling is carried out after heating to 70-95°C; The aging treatment is specifically as follows: The pre-aged plate is heated to 230°C at a rate of >30°C / h or at 270°C in furnace gas, and then cooled after being kept at this temperature for 10 to 12 hours.

2. The heat treatment process according to claim 1, characterized in that: The solution treatment is carried out by heating the temperature to 550-565° C. in an air cushion furnace, keeping the temperature for 15-60 seconds and then quenching with water.

3. The heat treatment process according to claim 1 or 2, characterized in that: The solution treatment further includes straightening, wherein the straightening is 0.3-1.5%.

4. The heat treatment process according to claim 1, characterized in that: After coiling, the process is kept warm for 4 to 8 hours or cooled naturally to room temperature.

5. The heat treatment process according to claim 1, characterized in that: The cooling is carried out by air cooling to room temperature at a rate of >10°C / h.

6. The heat treatment process according to claim 1, characterized in that: In the pre-aging treatment, the furnace gas temperature is 95-105°C, and the heating temperature is 75-90°C.

7. The heat treatment process according to claim 1, characterized in that: During the aging treatment, the heating rate is 35-45° C. / h.

8. The heat treatment process according to claim 5, characterized in that: The cooling rate is 15-20°C / h.

9. The heat treatment process according to any one of claims 1 to 8, characterized in that: The 6xxx aluminum alloy, measured by mass percentage, Comprising: Si: 0.3-1.8%, Fe: 0-0.4%, Cu: 0.1-0.9%, Mn: 0.1-0.45%, Mg: 0.1-1.4%, Cr: 0-0.3%, Ti: 0-0.1%, and the balance is Al.

10. An automobile anti-collision beam, prepared from a 6xxx aluminum alloy plate obtained by the heat treatment process according to any one of claims 1 to 9.

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