Heat treatment process of 5xxx aluminum alloy and alloy for automobile

Abstract

The invention provides a heat treatment process of a 5xxx aluminum alloy, which comprises the following steps: S1) carrying out continuous annealing heat treatment on the cold-rolled 5xxx aluminum alloy to obtain an annealed aluminum alloy; s2) carrying out stabilization heat treatment on the annealed aluminum alloy; the stabilization heat treatment specifically comprises the steps that the annealed aluminum alloy is heated to 280-340 DEG C at the speed of 8-60 DEG C / h in a staged mode, after heat preservation is conducted, the temperature is reduced to 180-210 DEG C at the speed of 5-15 DEG C / h, and then the temperature is reduced to the room temperature at the speed of 8-80 DEG C / h. In the heat treatment process, aluminum alloy grain recrystallization is achieved through continuous annealing heat treatment, grain boundary phases are regulated and controlled through stable heat treatment, the grain boundary phases are distributed discontinuously, and therefore the intergranular corrosion resistance of the 5xxx aluminum alloy is improved; meanwhile, the heat treatment process does not need to regulate and control components, casting, uniform fire, hot rolling, cold rolling and other preorder processes, only the heat treatment process is regulated and controlled, and operation and popularization are easy.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy material preparation, and in particular to a heat treatment process of a 5xxx aluminum alloy and an alloy for automobiles. Background Art

[0002] As a strategic emerging industry, the new energy vehicle industry carries the country's green strategy. Compared with fuel vehicles, its vehicle weight increases by 100 to 250 kg, and it is urgently needed to be lightweight to increase the driving range, reduce power consumption and carbon emissions. Due to its excellent lightweight, formability and corrosion resistance, 5xxx aluminum alloy plates do not require aging treatment and have become one of the most widely used aluminum alloy plate products in new energy vehicles. However, as an Al-Mg aluminum alloy, 5xxx alloy contains a high content of Mg, and the solid solution state of Mg is not stable; after long-term use, the grain boundary of 5xxx alloy will precipitate Al3Mg2 phase, which acts as an anode in a corrosive environment, and intergranular corrosion that can cause serious harm will occur, which is called "sensitization". The aluminum alloy plate for automobiles needs to be subsequently treated by electrophoresis, coating, spray painting and other baking treatments, which makes it easier to form Al3Mg2 phase at the grain boundary, reducing the intergranular corrosion resistance; and the sensitization problem will seriously affect the service life and service safety of the alloy, thereby threatening the safe operation of the vehicle.

[0003] In the prior art, the intergranular corrosion resistance of 5xxx alloys has been studied, and the research work has focused on 5083 alloys and 5754 alloys. There are few reports on the research of 5xxx alloys used in the automotive field, especially on the intergranular corrosion resistance after baking and the intergranular corrosion resistance during long-term service.

[0004] A Chinese patent with publication number CN115637359A discloses a corrosion-resistant 5083 aluminum alloy and a preparation method thereof. During the preparation process of the 5083 aluminum alloy, rare earth elements in a specific form and content are added, and specific smelting, casting and heat treatment processes are selected to prepare a 5083 aluminum alloy with relatively ideal corrosion resistance. However, the addition of rare earth elements is not conducive to promotion. At the same time, specific smelting, casting and heat treatment processes are required, which are difficult to operate.

[0005] A Chinese patent with publication number CN117604409A discloses a 5754 aluminum alloy plate with high intergranular corrosion resistance and a production method thereof. The intergranular corrosion resistance of the 5754 aluminum alloy plate can meet the technical requirements of new energy vehicles for materials by designing the alloy chemical composition, controlling the hot rolling reduction rate and temperature, and heat treatment process; however, its Mg content is 2.76-3.01%, and its corrosion resistance tendency is lower than that of the 5xxx alloy; in addition, the patent requires coordinated control of multiple processes such as the chemical composition of the alloy, the hot rolling reduction rate and temperature, and the heat treatment, which is difficult to operate and promote.

[0006] Therefore, providing a heat treatment process for 5xxx aluminum alloys to improve intergranular corrosion is of great significance for the widespread application of the alloy. Summary of the invention

[0007] The technical problem solved by the present invention is to provide a heat treatment process for 5xxx aluminum alloy. After the heat treatment process, the 5xxx aluminum alloy has excellent intergranular corrosion resistance in the two states of baking and pre-stretching + baking + sensitization.

[0008] In view of this, the present application provides a heat treatment process for a 5xxx aluminum alloy, comprising the following steps:

[0009] S1) performing continuous annealing heat treatment on the cold-rolled 5xxx aluminum alloy to obtain an annealed aluminum alloy;

[0010] S2) subjecting the annealed aluminum alloy to stabilization heat treatment;

[0011] The stabilization heat treatment is specifically as follows: the annealed aluminum alloy is heated to 280-340°C at a rate of 8-60°C / h, and after heat preservation, the temperature is lowered to 180-210°C at a rate of 5-15°C / h, and then the temperature is lowered to room temperature at a rate of 8-80°C / h.

[0012] Preferably, the continuous annealing heat treatment is specifically:

[0013] The cold rolled 5xxx aluminum alloy is heated to 510-530°C, kept at this temperature for 15-60s, and then water quenched.

[0014] Preferably, the water quenching further comprises straightening, and the straightening is 0.3-1.5%.

[0015] Preferably, the stage heating is specifically:

[0016] The temperature is raised to 120-140°C at a rate of 50-60°C / h, then to 150-180°C at a rate of 15-20°C / h, then to 200-250°C at a rate of 8-12°C / h, and finally to 280-340°C at a rate of 5-10°C / h.

[0017] Preferably, the stage heating is specifically:

[0018] The temperature is raised to 125-135°C at a rate of 55-60°C / h, then to 165-175°C at a rate of 18-20°C / h, then to 205-230°C at a rate of 8-10°C / h, and finally to 300-340°C at a rate of 8-9°C / h.

[0019] Preferably, the insulation time is 2 to 4 hours.

[0020] Preferably, during the stabilization heat treatment, the temperature reduction is specifically:

[0021] The temperature is lowered to 190-200°C at a rate of 8-12°C, then to 150-175°C at a rate of 30-80°C / h, then to 100-140°C at a rate of 20-60°C / h, then to 70-90°C at a rate of 15-30°C / h, and finally to room temperature at a rate of 5-20°C / h.

[0022] Preferably, the 5xxx aluminum alloy comprises, by mass percentage, the following: Si: 0-0.5%, Fe: 0-0.5%, Cu: 0-0.3%, Mn: 0.2-1.2%, Mg: 3-6%, Cr: 0-0.4%, Ti: 0-0.1%, Zn: 0-0.4%, and the balance is Al.

[0023] Preferably, the intergranular corrosion weight loss of the 5xxx aluminum alloy after stabilization heat treatment after baking is less than 10 mg / cm 2 , or, the intergranular corrosion weight loss of the 5xxx aluminum alloy after the stabilized heat treatment is less than 20 mg / cm after 5% pre-stretching + baking + sensitization treatment 2 .

[0024] The present application also provides an alloy for automobiles, including a 5xxx aluminum alloy obtained by the heat treatment process.

[0025] The present application provides a heat treatment process for a 5xxx aluminum alloy, which firstly subjects the cold-rolled 5xxx aluminum alloy to a continuous annealing heat treatment to obtain an annealed aluminum alloy; then subjects the annealed aluminum alloy to a stabilization heat treatment, wherein a stabilization heat treatment method of heating up and cooling down in stages is specifically adopted during the stabilization heat treatment process; in the above heat treatment process, the continuous annealing heat treatment realizes the recrystallization of the aluminum alloy grains, while the stabilization heat treatment regulates the grain boundary phase so that the grain boundary phase is discontinuously distributed, thereby improving the intergranular corrosion resistance of the 5xxx aluminum alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a metallographic photograph of the grain boundary structure of the 5xxx alloy plate of Example 2;

[0027] Figure 2 This is a metallographic photograph of the grain boundary phase structure of the 5xxx alloy plate of Example 2 after baking;

[0028] Figure 3 This is a metallographic photograph of the grain boundary phase structure of the 5xxx alloy plate of Example 2 after 5% pre-stretching + baking treatment + 120°C × 48h sensitization treatment;

[0029] Figure 4A metallographic photograph of the grain boundary structure of the 5xxx alloy plate of Comparative Example 4;

[0030] Figure 5 This is a metallographic photograph of the grain boundary structure of the 5xxx alloy plate of Comparative Example 4 after baking;

[0031] Figure 6 This is a metallographic photograph of the grain boundary phase structure of the 5xxx alloy plate of Comparative Example 4 after 5% pre-stretching + baking treatment + 120℃×48h sensitization treatment. DETAILED DESCRIPTION

[0032] 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.

[0033] In view of the performance requirements of automotive materials in the prior art and the problem that 5xxx aluminum alloys are difficult to meet the intergranular corrosion resistance, the present application provides a heat treatment process for 5xxx aluminum alloys, which does not require cumbersome coordinated control of multiple processes such as alloy composition, casting, soaking, hot rolling, cold rolling, etc. It only introduces a continuous annealing process and a stabilization heat treatment, and controls specific process means, and fully considers the two states of baking and pre-stretching + baking + sensitization required for automotive plates, so that the 5xxx aluminum alloy after heat treatment has excellent intergranular corrosion resistance in the above two states. Specifically, the embodiment of the present invention discloses a heat treatment process for 5xxx aluminum alloys, comprising the following steps:

[0034] S1) performing continuous annealing heat treatment on the cold-rolled 5xxx aluminum alloy to obtain an annealed aluminum alloy;

[0035] S2) subjecting the annealed aluminum alloy to stabilization heat treatment;

[0036] The stabilization heat treatment is specifically as follows: the annealed aluminum alloy is heated to 280-340°C at a rate of 8-60°C / h, and after heat preservation, the temperature is lowered to 180-210°C at a rate of 5-15°C / h, and then lowered to room temperature at a rate of 8-80°C / h.

[0037] In the heat treatment process of the 5xxx aluminum alloy provided in the present application, the cold-rolled 5xxx aluminum alloy is first subjected to continuous annealing heat treatment to obtain an annealed aluminum alloy; the continuous annealing heat treatment is to achieve grain recrystallization. In order to achieve the above-mentioned structural transformation, the continuous annealing heat treatment is specifically as follows:

[0038] The cold rolled 5xxx aluminum alloy is heated to 510-530°C, kept at this temperature for 15-60s, and then water quenched.

[0039] The above-mentioned 5xxx aluminum alloy after cold rolling specifically refers to the 5xxx aluminum alloy that is subjected to the above-mentioned heat treatment after cold rolling. The cold rolling can adopt technical means familiar to those skilled in the art. The relevant technical means before cold rolling are technical means familiar to those skilled in the art, and this application does not impose any special restrictions on this. The above-mentioned continuous annealing heat treatment is preferably carried out in an air cushion furnace. In the above-mentioned continuous annealing heat treatment, the temperature is raised to 515-525°C and kept warm for 20-45s; for example, in this application, the temperature is raised to 511°C, 512°C, 513°C, 514°C, 516°C, 517°C, 518°C, 519°C, 520°C, 521°C, 522°C, 523°C, 524°C, 526°C, 527°C, 528°C or 529°C, and kept warm for 16s, 17s, 18s, 19s, 21s, 22s, 23s, 24s, 25s, 26s, 27s, 28s, 29s, 30s, 31s, 32s, 33s, 34s, 35s, 36s, 37s, 38s, 39s, 40s, 41s, 42s, 43s, 44s, 46s, 47s, 48s, 49s, 50s, 51s, 52s, 53s, 54s, 55s, 56s, 57s, 58s or 59s.

[0040] According to the present invention, straightening is further included after the water quenching, and the straightening is 0.3-1.5%.

[0041] The present application then performs a stabilization heat treatment on the annealed aluminum alloy to regulate the discontinuous distribution of the grain boundary phase; the stabilization heat treatment preferably adopts a box-type stabilization heat treatment, and the stabilization heat treatment adopts a heat treatment method of stage heating and stage cooling, and the stage heating is specifically:

[0042] The temperature is raised to 120-140°C at a rate of 50-60°C / h, then to 150-180°C at a rate of 15-20°C / h, then to 200-250°C at a rate of 8-12°C / h, and finally to 280-340°C at a rate of 5-10°C / h.

[0043] More specifically, the stage temperature rise is:

[0044] The temperature is raised to 125-135°C at a rate of 55-60°C / h, then to 165-175°C at a rate of 18-20°C / h, then to 205-230°C at a rate of 8-10°C / h, and finally to 300-340°C at a rate of 8-9°C / h.

[0045] In a specific embodiment, the stage heating is:

[0046] The temperature was raised from room temperature to 125°C at a rate of 60°C / h, then to 165°C at a rate of 18°C / h, then to 205°C at a rate of 10°C / h, and finally to 340°C at a rate of 8°C / h.

[0047] In this application, after the above-mentioned stage heating, the temperature is kept for 2 to 4 hours and then the temperature is cooled in stages. The stage cooling is specifically as follows:

[0048] Cooling at a rate of 8 to 12°C to 190 to 200°C, then cooling at a rate of 30 to 80°C / h to 150 to 175°C, then cooling at a rate of 20 to 60°C / h to 100 to 140°C, then cooling at a rate of 15 to 30°C / h to 70 to 90°C, and finally cooling to room temperature at a rate of 5 to 20°C / h;

[0049] More specifically, the stage cooling is:

[0050] The temperature is lowered to 190-200°C at a rate of 9-10°C, then to 160-170°C at a rate of 40-70°C / h, then to 120-130°C at a rate of 28-40°C / h, then to 80-90°C at a rate of 18-25°C / h, and finally to room temperature at a rate of 8-16°C / h.

[0051] During the above-mentioned stage cooling process, the initial cooling temperature starts from the highest temperature of the stage heating as the starting temperature.

[0052] In the present application, the 5xxx aluminum alloy includes, by mass percentage, Si: 0-0.5%, Fe: 0-0.5%, Cu: 0-0.3%, Mn: 0.2-1.2%, Mg: 3-6%, Cr: 0-0.4%, Ti: 0-0.1%, Zn: 0-0.4%, and the balance is Al.

[0053] The 5xxx aluminum alloy plate after heat treatment in this application is then subjected to 125℃×15min+185℃×20min+160℃×15min+150℃×15min+140℃×30min, and each stage is heated to temperature and then air-cooled to room temperature for baking. The intergranular corrosion weight loss after the treatment is less than 10mg / cm 2 ; or, after heat treatment, 5xxx aluminum alloy plate is subjected to 5% pre-stretching + 125℃×15min+185℃×20min+160℃×15min+150℃×15min+140℃×30min, each stage is cooled to room temperature after temperature setting and heat preservation, and then baked at 120℃×48h, and the intergranular corrosion weight loss after sensitization treatment is less than 20mg / cm 2 .

[0054] The present application also provides an automotive alloy, which includes a 5xxx aluminum alloy obtained by the above heat treatment process.

[0055] The present application provides a heat treatment process for a 5xxx aluminum alloy, which comprises the following steps: comprising the following steps: S1) subjecting the cold-rolled 5xxx aluminum alloy to continuous annealing heat treatment to obtain an annealed aluminum alloy; S2) subjecting the annealed aluminum alloy to a stabilization heat treatment; the stabilization heat treatment is specifically as follows: heating the annealed aluminum alloy to 280 to 340°C in stages at a rate of 8 to 60°C / h, and after heat preservation, cooling to 180 to 210°C at a rate of 5 to 15°C / h, and then cooling to room temperature at a rate of 8 to 80°C / h. In the traditional process, 5xxx aluminum alloy cold-rolled sheet is directly subjected to low-temperature annealing to achieve recrystallization and stabilization. However, low-temperature annealing involves two processes, recrystallization and stabilization, which result in continuous grain boundary phase and poor intergranular corrosion resistance. Industrial box-type stabilization annealing involves slow heating and slow cooling processes, which easily lead to the precipitation and continuous precipitation of grain boundary phase during the heating process, and difficulty in discontinuity during the insulation process. During the cooling process, the grain boundary phase further precipitates and coarsens, which also results in poor intergranular corrosion resistance. The present invention achieves grain recrystallization through continuous annealing. During the stabilization heat treatment process, the discontinuous distribution of the grain boundary phase is regulated by controlling the heating and cooling rates, the insulation temperature and time, thereby improving the intergranular corrosion resistance.

[0056] This heat treatment process does not require the control of a series of preceding processes such as alloy composition, melting, annealing, hot rolling, and cold rolling. It has few process controls and is easy to promote. Moreover, it is developed based on industrial production technology and equipment, and the process has good batch operability.

[0057] In order to further understand the present invention, the heat treatment process of the 5xxx 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.

[0058] Example 1

[0059] S1) performing a finished product annealing treatment on the 5xxx alloy cold-rolled sheet, wherein the annealing treatment adopts an online continuous annealing in an air cushion furnace, the cold-rolled sheet is heated to 510° C. in the air cushion furnace, the holding time is 60 seconds, water quenched, and straightened by 0.3% to obtain an annealed sheet;

[0060] S2) subjecting the annealed sheet to a stabilization heat treatment, wherein the stabilization heat treatment is a box annealing, wherein a stage heating method is first adopted and then a stage cooling method is adopted, specifically:

[0061] The temperature was increased from room temperature to 125°C at 60°C / h, from 125°C to 165°C at 18°C / h, from 165°C to 205°C at 10°C / h, from 205°C to 340°C at 8°C / h, and kept warm for 2h; then the temperature was decreased from 340°C to 200°C at 10°C / h, from 200°C to 175°C at 40°C / h, from 175°C to 120°C at 28°C / h, from 120°C to 80°C at 15°C / h, and from 80°C to room temperature at 8°C / h to obtain a 5xxx aluminum alloy plate.

[0062] Example 2

[0063] S1) annealing the 5xxx alloy cold-rolled sheet, wherein the annealing is performed by online continuous annealing in an air cushion furnace, the cold-rolled sheet is heated to 530° C. in the air cushion furnace, the holding time is 15 s, water quenched, and straightened by 1.5% to obtain an annealed sheet;

[0064] S2) subjecting the annealed sheet to a stabilization heat treatment, wherein the stabilization heat treatment is a box annealing, wherein a stage heating method is first adopted and then a stage cooling method is adopted, specifically:

[0065] The temperature was increased from room temperature to 125°C at 60°C / h, from 125°C to 165°C at 18°C / h, from 165°C to 205°C at 10°C / h, from 205°C to 280°C at 8°C / h, and kept warm for 2h; then the temperature was decreased from 280°C to 200°C at 10°C / h, from 200°C to 175°C at 40°C / h, from 175°C to 120°C at 28°C / h, from 120°C to 80°C at 15°C / h, and from 80°C to room temperature at 8°C / h to obtain a 5xxx aluminum alloy plate.

[0066] Example 3

[0067] S1) annealing the 5xxx alloy cold-rolled sheet, wherein the annealing is performed by online continuous annealing in an air cushion furnace, the cold-rolled sheet is heated to 510° C. in the air cushion furnace, the temperature is kept at this temperature for 60 seconds, water quenched, and straightened by 0.3% to obtain an annealed sheet;

[0068] S2) subjecting the annealed sheet to a stabilization heat treatment, wherein the stabilization heat treatment is a box annealing, wherein a stage heating method is first adopted and then a stage cooling method is adopted, specifically:

[0069] The temperature was increased from room temperature to 125°C at 60°C / h, from 125°C to 165°C at 18°C / h, from 165°C to 205°C at 10°C / h, from 205°C to 280°C at 8°C / h, and kept warm for 2h; then the temperature was decreased from 280°C to 200°C at 15°C / h, from 200°C to 175°C at 80°C / h, from 175°C to 120°C at 56°C / h, from 120°C to 80°C at 30°C / h, and from 80°C to room temperature at 16°C / h to obtain a 5xxx aluminum alloy plate.

[0070] Comparative Example 1

[0071] The 5xxx alloy cold-rolled sheet is directly subjected to stabilization heat treatment, which is box annealing, first adopting a stage heating method and then a stage cooling method, specifically:

[0072] The temperature was increased from room temperature to 125°C at 60°C / h, from 125°C to 165°C at 18°C / h, from 165°C to 205°C at 10°C / h, from 205°C to 340°C at 8°C / h, and kept warm for 2h; then the temperature was decreased from 340°C to 200°C at 10°C / h, from 200°C to 175°C at 40°C / h, from 175°C to 120°C at 28°C / h, from 120°C to 80°C at 15°C / h, and from 80°C to room temperature at 8°C / h to obtain a 5xxx aluminum alloy plate.

[0073] Comparative Example 2

[0074] S1) annealing the 5xxx alloy cold-rolled sheet, wherein the annealing is performed by online continuous annealing in an air cushion furnace, the cold-rolled sheet is heated to 510-530° C. in the air cushion furnace, the holding time is 15-60 seconds, water quenched, and straightened by 0.3-1.5% to obtain an annealed sheet;

[0075] S2) subjecting the annealed sheet to a stabilization heat treatment, wherein the stabilization heat treatment is a box annealing, wherein a stage heating method is first adopted and then a stage cooling method is adopted, specifically:

[0076] The temperature was increased from room temperature to 125°C at 60°C / h, from 125°C to 165°C at 18°C / h, from 165°C to 205°C at 10°C / h, from 205°C to 280°C at 8°C / h, and kept warm for 2h; then the temperature was decreased from 280°C to 230°C at 60°C / h, from 230°C to 175°C at 40°C / h, from 175°C to 120°C at 28°C / h, from 120°C to 80°C at 15°C / h, and from 80°C to room temperature at 8°C / h to obtain a 5xxx aluminum alloy plate.

[0077] Comparative Example 3

[0078] The 5xxx alloy cold-rolled sheet is annealed, wherein the annealing treatment is performed by online continuous annealing in an air cushion furnace, the cold-rolled sheet is heated to 530° C. in the air cushion furnace, the heat preservation time is 60 s, water quenched, and straightened by 0.3% to obtain a finished annealed sheet.

[0079] Comparative Example 4

[0080] S1) annealing the 5xxx alloy cold-rolled sheet, wherein the annealing is performed by online continuous annealing in an air cushion furnace, the cold-rolled sheet is heated to 510-530° C. in the air cushion furnace, the holding time is 15-60 seconds, water quenched, and straightened by 0.3-1.5% to obtain an annealed sheet;

[0081] S2) subjecting the annealed sheet to a stabilization heat treatment, wherein the stabilization heat treatment is a box annealing, wherein a stage heating method is first adopted and then a stage cooling method is adopted, specifically:

[0082] The temperature was increased from room temperature to 125°C at 60°C / h, then increased from 125°C to 165°C at 18°C / h, then increased from 165°C to 205°C at 10°C / h, then increased from 205°C to 240°C at 8°C / h, and kept warm for 2h; then the temperature was decreased from 240°C to 200°C at 10°C / h, then decreased from 200°C to 175°C at 40°C / h, then decreased from 175°C to 120°C at 28°C / h, then decreased from 120°C to 80°C at 15°C / h, and finally decreased from 80°C to room temperature at 8°C / h to obtain a 5xxx aluminum alloy plate.

[0083] The composition of the 5xxx alloy in the above embodiments and comparative examples is specifically: Si: 0.05%, Fe: 0.13%, Cu: 0.15%, Mn: 0.25%, Mg: 5.0%, Cr: 0.1%, Ti: 0.03%, Zn: 0.1%, and the balance is Al.

[0084] The aluminum alloy sheets prepared in the comparative example and the example are subjected to baking treatment or pre-stretching + baking + sensitization, wherein the baking process is 125℃×15min+185℃×20min+160℃×15min+150℃×15min+140℃×30min, each stage is air-cooled to room temperature after being placed and kept warm, the pre-stretching process is 5%, and the sensitization process is 120℃ / 48h. After the above, the intergranular corrosion weight loss of the comparative example and the example aluminum alloy sheets are tested in turn according to the ASTM G67 standard; the performance of the 5xxx alloy sheets of Examples 1 to 3 and Comparative Examples 1 to 4 is compared as shown in Table 1;

[0085] Table 1 Intergranular corrosion weight loss data of 5xxx alloy plates prepared in different embodiments and comparative examples

[0086]

[0087]

[0088] As shown in Table 1, the intergranular corrosion resistance of the 5xxx alloy plate treated by the process of the present invention is significantly improved. Therefore, in the heat treatment process, it is necessary to strictly control the finished product annealing process and stabilize the annealing heating and cooling speed, insulation temperature, and insulation time.

[0089] The grain boundary phase of the 5xxx alloy plate obtained in Comparative Example 1 is a continuous phase, and the grain boundary remains continuous after baking treatment and pre-stretching + baking + sensitization treatment. Compared with Example 1, Comparative Example 1 lacks the finished product annealing treatment process, so it is necessary to ensure that the finished product must first undergo an annealing process.

[0090] The intergranular corrosion loss of the 5xxx alloy plate obtained in Comparative Example 2 after baking treatment and pre-stretching + baking + sensitization treatment is greater than that of the plate in Example 2. Compared with Example 2, Comparative Example 2 lacks the staged temperature reduction control from 280℃ to 180-210℃ and then cooling to room temperature. For this purpose, staged temperature reduction control with 180-210℃ as the boundary point is required.

[0091] No grain boundary phase was observed in the 5xxx alloy plate obtained in Comparative Example 3, but the grain boundaries remained continuous after baking treatment and pre-stretching + baking + sensitization treatment, and the intergranular corrosion loss was greater than that of the plates obtained in Examples 1 to 4. Compared with Examples 1 to 4, Comparative Example 3 lacks a stabilization annealing treatment step, so a stabilization annealing step must be included.

[0092] Comparative Example 4 obtains a continuous distribution of grain boundary phases in the 5xxx alloy plate, such as Figure 4 As shown, Example 2 obtains a discontinuous distribution of the grain boundary phase of the 5xxx alloy plate, as shown Figure 1 As shown. In comparative example 4, the grain boundary continuity is aggravated after baking treatment and pre-stretching + baking + sensitization treatment, as shown Figure 5 , 6 As shown, after baking treatment and pre-stretching + baking + sensitization treatment, the grain boundary phase of the 5xxx alloy plate in Example 2 still maintains a discontinuous distribution, as shown in FIG. Figure 2 , 3 The intergranular corrosion weight loss is greater than that of the plates in Examples 1 and 2. The stabilization annealing temperature of Comparative Example 4 is lower than that of Examples 1 and 2, so the stabilization annealing temperature must be controlled to a suitable temperature.

[0093] In the heat treatment process of 5xxx alloy plates in Examples 1 to 3, the holding temperature and the cooling method are controlled respectively. The intergranular corrosion weight loss of the two states of baking and pre-stretching + baking + sensitization is different. The intergranular corrosion weight loss after baking treatment is <10 mg / cm 2 , the intergranular corrosion weight loss of 5xxx aluminum alloy plate prepared by the process of Examples 1 to 3 after 5% pre-stretching + baking treatment + 120℃×48h sensitization treatment is less than 20mg / cm 2 .

[0094] The results of the above Examples 1 to 3 and Comparative Examples 1 to 4 show that the present invention strictly limits the annealing process and the stabilization annealing process, controls the stabilization annealing heating and cooling speeds and the insulation temperature, and regulates the discontinuity of the grain boundary phase, thereby improving the intergranular corrosion resistance of the 5xxx aluminum alloy plate in both the baking and pre-stretching + baking + sensitization states, and can be applied to the automotive field.

[0095] 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.

[0096] 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 5xxx aluminum alloy, comprising the following steps: S1) performing continuous annealing heat treatment on the cold-rolled 5xxx aluminum alloy to obtain an annealed aluminum alloy; S2) subjecting the annealed aluminum alloy to stabilization heat treatment; The stabilization heat treatment is specifically as follows: the annealed aluminum alloy is heated to 280-340°C at a rate of 8-60°C / h, and after heat preservation, the temperature is lowered to 180-210°C at a rate of 5-15°C / h, and then the temperature is lowered to room temperature at a rate of 8-80°C / h.

2. The heat treatment process according to claim 1, characterized in that: The continuous annealing heat treatment is specifically: The cold rolled 5xxx aluminum alloy is heated to 510-530°C, kept at this temperature for 15-60s, and then water quenched.

3. The heat treatment process according to claim 2, characterized in that: The water quenching also includes straightening, and the straightening is 0.3-1.5%.

4. The heat treatment process according to claim 1, characterized in that: The stage heating is specifically as follows: The temperature is raised to 120-140°C at a rate of 50-60°C / h, then to 150-180°C at a rate of 15-20°C / h, then to 200-250°C at a rate of 8-12°C / h, and finally to 280-340°C at a rate of 5-10°C / h.

5. The heat treatment process according to claim 1 or 4, characterized in that: The stage heating is specifically as follows: The temperature is raised to 125-135°C at a rate of 55-60°C / h, then to 165-175°C at a rate of 18-20°C / h, then to 205-230°C at a rate of 8-10°C / h, and finally to 300-340°C at a rate of 8-9°C / h.

6. The heat treatment process according to claim 1, characterized in that: The insulation time is 2 to 4 hours.

7. The heat treatment process according to claim 1, characterized in that: During the stabilization heat treatment, the temperature reduction is specifically: The temperature is lowered to 190-200°C at a rate of 8-12°C, then to 150-175°C at a rate of 30-80°C / h, then to 100-140°C at a rate of 20-60°C / h, then to 70-90°C at a rate of 15-30°C / h, and finally to room temperature at a rate of 5-20°C / h.

8. The heat treatment process according to any one of claims 1 to 7, characterized in that: The 5xxx aluminum alloy includes, by mass percentage, Si: 0-0.5%, Fe: 0-0.5%, Cu: 0-0.3%, Mn: 0.2-1.2%, Mg: 3-6%, Cr: 0-0.4%, Ti: 0-0.1%, Zn: 0-0.4%, and the balance is Al.

9. The heat treatment process according to claim 8, characterized in that: The intergranular corrosion weight loss of the 5xxx aluminum alloy after stabilization heat treatment after baking is less than 10 mg / cm 2 , or, the intergranular corrosion weight loss of the 5xxx aluminum alloy after the stabilized heat treatment is less than 20 mg / cm after 5% pre-stretching + baking + sensitization treatment 2 .

10. An alloy for automobiles, comprising a 5xxx aluminum alloy obtained by the heat treatment process of any one of claims 1 to 9.

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