A heat treatment process for obtaining aluminum-magnesium-silicon alloy with high comprehensive performance

Abstract

The present invention relates to a heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance; it belongs to the technical field of non-ferrous metal heat treatment processes. The method comprises the following steps: subjecting an aluminum alloy sample to solid solution treatment and heat preservation, cooling the sample to the starting temperature of variable temperature step quenching after solid solution treatment, then heating the sample to the ending temperature of variable temperature step quenching at a heating rate greater than 5°C / min, and then cooling the sample to the starting temperature of variable temperature step quenching; the starting temperature of variable temperature step quenching is not lower than 50°C, the ending temperature of variable temperature step quenching is not higher than 200°C, and the duration of cooling from the ending temperature of variable temperature step quenching to the starting temperature of variable temperature step quenching is not less than 30 minutes; then performing a rapid cooling treatment, and finally performing an aging treatment to obtain the product. The aluminum alloy prepared by the process of the present invention has excellent strength and plasticity and good corrosion resistance, which can significantly improve the service life of the material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy heat treatment process, and particularly relates to a heat treatment method for improving comprehensive performance of an aluminum-magnesium-silicon alloy. BACKGROUND

[0002] Aluminum alloy material is a very important material in the field of transportation. With the increasing energy crisis and environmental problems, weight reduction of various transportation tools has become an effective alleviating means. Among them, aluminum alloy, especially Al-Mg-Si alloy, is widely used in marine transportation tools and energy vehicles due to its excellent plasticity, good strength, low production cost, low processing difficulty and good corrosion resistance.

[0003] Traditional methods for improving the performance of aluminum alloy mainly include micro-alloying, powder metallurgy, spray forming and various aging systems. In recent years, large deformation technologies such as high-pressure torsion and equal-channel angular extrusion have also appeared, which can improve the performance of the alloy by refining the microstructure of the alloy. However, these technologies still have the disadvantages of limited sample size, high cost and difficult operation. At the same time, the Hall-Petch coefficient of aluminum alloy is low, and the fine-grain strengthening is not obvious. In contrast, the heat treatment process is more economical, simple and easy to continuous production, and the final precipitation strengthening is very significant for improving the performance of aluminum alloy material.

[0004] At present, there are many researches on the heat treatment process of 6-series aluminum alloy, such as CN202210032759.2 and CN202010646065.9. However, most of them are still limited to the change of temperature in the traditional heat treatment system, and the change of micro-alloying elements, which makes the overall process more complex and the processing window more strict. In addition, few studies focus on the synergistic effect of heat treatment system on the mechanical properties and corrosion resistance of materials. Therefore, it is necessary to develop a new process to simplify the heat treatment system and improve the strength and corrosion resistance of the material. SUMMARY

[0005] In view of the problems of insufficient quenching rate of Al-Mg-Si alloy with high quenching sensitivity under current industrial production conditions, negative effects of natural aging at room temperature, poor material performance, and poor coordination between corrosion resistance and mechanical properties of aluminum alloy for marine engineering, the application provides a heat treatment method for further improving corrosion resistance while ensuring reasonable mechanical strength.

[0006] The application provides a heat treatment process for obtaining aluminum-magnesium-silicon alloy with high comprehensive performance, which comprises the following steps:

[0007] Step 1: solid solution treatment

[0008] The Al-Mg-Si alloy is heated to a solid solution temperature for a period of time, then furnace-cooled or air-cooled or water-cooled to a step quenching starting temperature, and the quenching transfer time is not more than 5s, and the solid solution treatment temperature is not less than 500℃;

[0009] Step two: variable temperature step quenching

[0010] The sample obtained in step one is cooled to a variable temperature step quenching starting temperature, then heated to a variable temperature step quenching ending temperature at a heating rate of greater than 5℃ / min, and then cooled to the variable temperature step quenching starting temperature; the variable temperature step quenching starting temperature is not less than 50℃, the variable temperature step quenching ending temperature is not higher than 200℃, and the duration from the variable temperature step quenching ending temperature to the variable temperature step quenching starting temperature is not less than 30min; the variable temperature step quenching ending temperature is higher than the variable temperature step quenching starting temperature.

[0011] Step three: rapid cooling treatment

[0012] The sample obtained in step two is subjected to rapid cooling treatment.

[0013] Step four: final aging treatment

[0014] The cryogenic deformation sample obtained in step three is subjected to final aging treatment to obtain a finished product.

[0015] As preferred, in step one, the solid solution temperature of the sample is 500℃-580℃, further preferably 525-580℃, and more further preferably 550-580℃, and the solid solution time is 30min-90min, further preferably 50-70min.

[0016] As preferred, in step two, after the solid solution holding, the sample is furnace-cooled or air-cooled or water-cooled to a variable temperature step quenching starting temperature, then rapid heating is started until the temperature reaches the ending temperature, and the rapid heating mode includes direct heating by resistance wire, salt bath furnace, and air furnace heating; then the temperature is lowered to the starting temperature at a certain temperature rate, the variable temperature step quenching starting temperature is 45℃-125℃, the variable temperature step quenching ending temperature is 100-200℃, the temperature lowering rate when lowering to the starting temperature is 1℃ / min-10℃ / min, and the duration is 0.5h-2h, and the variable temperature step quenching ending temperature is higher than the variable temperature step quenching starting temperature.

[0017] As a further preferred scheme, in step two, the rapid heating rate is 8-15℃ / min.

[0018] As a further preferred scheme, in step two, the variable temperature step quenching starting temperature is 50℃-100℃, and the ending temperature is 100-200℃.

[0019] As a further preferred embodiment, in step two, the temperature of the temperature step quenching is from 65°C to 95°C, and the final temperature is from 125°C to 155°C.

[0020] As a still further preferred embodiment, in step two, the temperature of the temperature step quenching is from 65°C to 75°C, and the final temperature is from 125°C to 135°C.

[0021] As a preferred embodiment, in step three of the heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance, the medium for the rapid cooling treatment is cold water, ice water, dry ice, liquid nitrogen, etc., and the temperature of the sample after quenching is not higher than room temperature.

[0022] As a preferred embodiment, in step four of the heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance, the final aging treatment is artificial aging, the aging temperature is from 150°C to 200°C, and the aging time is from 3h to 12h.

[0023] As a further preferred embodiment, in step four of the heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance, the final aging treatment is artificial aging, the aging temperature is from 170°C to 180°C, and the aging time is from 5h to 10h.

[0024] The aluminum-magnesium-silicon alloy contains 0.2wt% or less of Cu.

[0025] As a preferred embodiment, in the heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance, the composition of the aluminum-magnesium-silicon alloy includes the following components in mass percentage:

[0026] Mg 1.0-1.4%;

[0027] Si 1.0-1.4%;

[0028] Cu 0.05-0.15%

[0029] Al balance.

[0030] As a further preferred embodiment, in the heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance, the composition of the aluminum-magnesium-silicon alloy includes the following components in mass percentage:

[0031] Mg 1.1-1.3%;

[0032] Si 1.1-1.3%;

[0033] Cu 0.08-0.12%

[0034] Al balance.

[0035] As a further preferred embodiment, the present application provides a heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance, the composition of the aluminum-magnesium-silicon alloy includes the following components in percentage by mass:

[0036] Mg 1.2~1.3%;

[0037] Si 1.1~1.3%;

[0038] Cu 0.09~0.11%

[0039] Al balance. The present application has the following advantages:

[0040] The present application designs a new type of hierarchical quenching method, which is different from the traditional quenching method in that the new type of hierarchical quenching method balances the vacancy quenching rate and the migration rate of solute atoms in the cooling stage, which is conducive to the rapid formation of higher number density of type II clusters, promotes subsequent artificial aging precipitation, and shortens the time required for peak aging.

[0041] After the solid solution treatment, the present application does not cool to room temperature but rather cools to the starting temperature of the variable temperature step quenching, because the type I clusters formed at room temperature are quite different from the strengthening phase beta" component, and it is difficult to transform into the beta" phase in the subsequent process; moreover, the type I clusters are formed very early, usually starting to form when the temperature is cooled to a lower temperature; then the temperature is raised to the end temperature of the variable temperature step quenching and controlled to be not higher than 200 DEG C in order to avoid the dissolution of clusters caused by too high temperature; then a lower cooling rate is adopted and the starting temperature of the variable temperature step quenching is controlled, and the time from the end temperature of the variable temperature step quenching to the starting temperature of the variable temperature step quenching is controlled to be greater than or equal to 30 min in order to provide sufficient atomic migration time to form higher number density of type II clusters;

[0042] Currently, the traditional quenching process is mostly direct water quenching, i.e. rapidly cooling to room temperature, which can retain more quenching vacancies, but these vacancies are basically consumed by the formation of type I small clusters, which has a negative impact on subsequent processing. In addition, a larger quenching rate (for example, using water or ice water quenching) can reduce the corrosion resistance (such as intergranular corrosion resistance) of the alloy material, because the continuous strengthening phase is precipitated at the grain boundary and the precipitate-free zone is relatively narrow, and the potential of the strengthening phase is higher than that of the matrix, and the continuous strengthening phase is conducive to the formation of a corrosion channel, so the corrosion resistance of the material is sharply reduced. Although slowing down the quenching rate can improve the corrosion resistance, the number of quenching vacancies is also reduced, and the precipitation kinetics is not sufficient to precipitate a sufficient number of strengthening phases, which has an adverse effect on the strength of the material. At present, there are also proposals to use pre-aging to solve the negative impact of natural aging, but pre-aging itself increases the process steps and processing time, in addition, the current is mostly isothermal pre-aging, which cannot achieve the best balance between vacancy quenching and solute atom transfer, and the type I clusters formed during natural aging consume a large amount of solute atoms, and at most pre-aging temperatures, they cannot be redissolved into the matrix, which limits the potential for improving the final strength.

[0043] Therefore, the present application adopts a new type of graded quenching method, which combines quenching and pre-aging steps, controls the cooling rate in a specific temperature range to affect the formation of multi-scale and multi-type clusters / GP zones. On the one hand, the starting temperature of the variable temperature step quenching is only slightly higher than room temperature, and the quenching rate is lower than that of water quenching, which can balance the corrosion resistance of the material and the number density of quenching vacancies, and also inhibits the rapid formation of type I clusters at room temperature to achieve higher mechanical properties in subsequent processing. On the other hand, during the variable temperature processing stage, the vacancy quenching rate and solute atom transfer rate are considered, and type II clusters and GP zones are formed to a greater extent, which not only forms a high-density strengthening phase in the subsequent processing stage, but also consumes Cu and Si atoms to avoid their enrichment at the grain boundary. The subsequent rapid cooling stage effectively preserves the microstructure formed in the previous stage, limits the transformation of the microstructure during the cooling process, and avoids the negative impact of natural aging on the material. At the same time, compared with the traditional quenching method, the distribution of precipitates at the grain boundary is improved. Therefore, the material has high mechanical properties and good corrosion resistance. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 Performance characterization chart of products obtained in the examples and comparative examples. DETAILED DESCRIPTION

[0045] Example 1:

[0046] The original sample was an extruded rod with a diameter of 32 mm, and the alloy composition was Al-1.2Mg-1.3Si-0.1Cu (mass fraction %). First, a solid solution treatment was performed at 570°C for 1 h, the obtained sample was cooled to 70°C in a salt bath furnace for 10 s, then rapidly heated to 130°C (the average heating rate was 12.5°C / min), then cooled to 70°C at a rate of 1°C / min, and quenched in ice water for 2 min. The sample after the variable temperature step quenching was subjected to artificial aging treatment at 170°C / 8h in a hot air circulating furnace. The yield strength of the obtained product was 340.4 MPa, the tensile strength was 383.6 MPa, the elongation was 15.8%, the corrosion potential of the obtained product was -0.67V, and the corrosion current density was 1.49×10 -7 A·cm 2 .(The electrochemical corrosion experiment used a classic three-electrode test system, in which the aluminum alloy was the working electrode, the platinum sheet (Pt) was the counter electrode, and the saturated calomel electrode was the reference electrode. The electrolyte medium for the potentiodynamic polarization curve test was a NaCI solution with a mass concentration of 3.5%, and the test temperature was room temperature. The working electrode was placed in the electrolyte solution for 1 hour before the test, and the self-corrosion potential of the aluminum alloy electrode was allowed to reach stability. The potential polarization range of the potentiodynamic polarization was -0.3V (vs. OCP) to +0.3V (vs. OCP), the scanning rate was 1mV / s, and the scanning step was 0.5mV. The corresponding self-corrosion potential and self-corrosion current were obtained by Tafel extrapolation.

[0047] Table 1 Corrosion performance of products obtained in examples and comparative examples

[0048]

[0049] Example 2:

[0050] The original sample was an extruded rod with a diameter of 32 mm, and the alloy composition was Al-1.2Mg-1.3Si-0.1Cu (mass fraction %). First, a solid solution treatment was performed at 570°C for 1 h, the obtained sample was cooled to 70°C in a salt bath furnace for 10 s, then rapidly heated to 130°C (the average heating rate was 12.5°C / min), then cooled to 70°C at a rate of 1°C / min, and quenched in ice water for 2 min. The sample after the variable temperature step quenching was subjected to artificial aging treatment at 170°C / 8h in a hot air circulating furnace. The yield strength of the obtained product was 340.4 MPa, the tensile strength was 383.6 MPa, the elongation was 15.8%, the corrosion potential of the obtained product was -0.67V, and the corrosion current density was 1.49×10 -7 A·cm 2(Experimental conditions for the determination of the corrosion potential and corrosion current of the product were the same as in Example 1).

[0051] Example 3:

[0052] The original sample was an extruded bar of 32 mm diameter and the alloy composition was Al-1.3Mg-1.1Si-0.1Cu (mass %). The sample was first solution treated at 530°C for 1 h, cooled to 90°C in a salt bath furnace for 10 s, then rapidly heated to 150°C (average heating rate of 12.5°C / min), then cooled to 90°C at a rate of 1°C / min, quenched using liquid nitrogen for 2 min. The sample after the variable temperature step quench was artificially aged at 175°C / 6 h in a hot air circulation furnace. The yield strength of the product obtained was 310.35 MPa, the tensile strength was 361.7 MPa, the elongation was 18.35%, the corrosion potential of the product obtained was -0.69 V, and the corrosion current density was 1.93 x 10 -7 A-cm 2 (Experimental conditions for the determination of the corrosion potential and corrosion current of the product were the same as in Example 1).

[0053] Comparative Example 1:

[0054] The original sample was an extruded bar of 32 mm diameter and the alloy composition was Al-1.3Mg-1.1Si-0.1Cu (mass %). The sample was first solution treated at 530°C for 1 h, cooled to 90°C in a salt bath furnace for 10 s, then rapidly heated to 150°C (average heating rate of 12.5°C / min), then cooled to 90°C at a rate of 1°C / min, quenched using liquid nitrogen for 2 min. The sample after the variable temperature step quench was artificially aged at 175°C / 6 h in a hot air circulation furnace. The yield strength of the product obtained was 310.35 MPa, the tensile strength was 361.7 MPa, the elongation was 18.35%, the corrosion potential of the product obtained was -0.69 V, and the corrosion current density was 1.93 x 10 -7 A-cm 2 (Experimental conditions for the determination of the corrosion potential and corrosion current of the product were the same as in Example 1).

[0055] Comparative Example 2:

[0056] The original sample was an extruded bar of 32 mm diameter and the alloy composition was Al-1.3Mg-1.1Si-0.1Cu (mass %). The sample was first solution treated at 530°C for 1 h, cooled to 90°C in a salt bath furnace for 10 s, then rapidly heated to 150°C (average heating rate of 12.5°C / min), then cooled to 90°C at a rate of 1°C / min, quenched using liquid nitrogen for 2 min. The sample after the variable temperature step quench was artificially aged at 175°C / 6 h in a hot air circulation furnace. The yield strength of the product obtained was 310.35 MPa, the tensile strength was 361.7 MPa, the elongation was 18.35%, the corrosion potential of the product obtained was -0.69 V, and the corrosion current density was 1.93 x 10 -7 A-cm 2 The product obtained in this comparative example has good corrosion resistance, but the mechanical strength is too low.

[0057] Comparative Example 3

[0058] The original sample was an extruded bar with a diameter of 32 mm, and the alloy composition was Al-1.3Mg-1.0Si-0.1Cu (mass %). First, a solid solution treatment was carried out at 550°C for 1 h, and the sample after solid solution treatment was subjected to step quenching, the step quenching temperature was 150°C, the holding time was 1 h, and then cold water quenching was carried out to room temperature, the holding time was 2 min. Subsequently, the sample was subjected to artificial aging treatment at 175°C / 6h in a hot air circulating furnace. The yield strength of the product obtained was 294.29 MPa, the tensile strength was 341.1 MPa, the elongation was 11.25%, the corrosion potential of the product obtained was -0.69V, and the corrosion current density was 5.97x10 -7 A-cm 2 (The specific experimental conditions and Example 1 are consistent when the corrosion potential and corrosion current of the product are measured).

Claims

1. A heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance, characterized in that; The steps include: Step 1: Solution treatment After heating the Al-Mg-Si alloy to the solution temperature and keeping it for a period of time, cool it with the furnace or air cool it or water cool it to the starting temperature of the step quenching. The quenching transfer time shall not exceed 5s, and the solution treatment temperature shall not be lower than 500℃. Step 2: Variable temperature step quenching Cooling the sample obtained in step 1 to the variable temperature step quenching starting temperature, then heating it to the variable temperature step quenching ending temperature at a heating rate greater than 5°C / min, and then cooling it to the variable temperature step quenching starting temperature; the variable temperature step quenching starting temperature is not less than 50°C, the variable temperature step quenching ending temperature is not higher than 200°C, and the duration of cooling from the variable temperature step quenching ending temperature to the variable temperature step quenching starting temperature is not less than 30 minutes; the variable temperature step quenching ending temperature is higher than the variable temperature step quenching starting temperature; In step 2, after solution insulation, the steel is cooled with the furnace or air-cooled or water-cooled to the starting temperature of the variable temperature step quenching, and then the temperature is rapidly increased until the temperature reaches the end temperature. The rapid heating method includes direct heating with a resistance wire, a salt bath furnace, and heating with an air furnace. The steel is then cooled to the starting temperature at a certain temperature rate. The starting temperature of the variable temperature step quenching is 45°C-125°C, and the end temperature of the variable temperature step quenching is 100-200°C. The cooling rate to the starting temperature at a certain temperature rate is 1°C / min-10°C / min, and the duration is 0.5h-2h. The end temperature of the variable temperature step quenching is higher than the starting temperature of the variable temperature step quenching. In step 2, the rapid heating rate is 8-15°C / min; Step 3: Rapid cooling The sample obtained in step 2 is subjected to rapid cooling treatment; Step 4: Final aging treatment The deep-cold deformed sample obtained in step 3 is subjected to final aging treatment to obtain a finished product; in step 4, the final aging treatment is artificial aging, the aging temperature is 150° C. to 200° C., and the aging time is 3 h to 12 h.

2. The heat treatment process for obtaining a high comprehensive performance aluminum-magnesium-silicon alloy according to claim 1, characterized in that: In step 1, the solution temperature of the sample is 500°C~580°C, and the solution time is 30min~90min.

3. The heat treatment process for obtaining a high comprehensive performance aluminum-magnesium-silicon alloy according to claim 1, characterized in that: In step 2, the starting temperature of the variable temperature step quenching is 50°C-100°C, and the ending temperature is 100-200°C.

4. The heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance according to claim 3, characterized in that: In step 2, the starting temperature of the variable temperature step quenching is 65°C-95°C, and the ending temperature is 125-155°C.

5. The heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance according to claim 4, characterized in that: In step 2, the starting temperature of the variable temperature step quenching is 65°C-75°C, and the ending temperature is 125-135°C.

6. The heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance according to claim 1, characterized in that: In step 3, the medium for rapid cooling treatment is selected from one of cold water, ice water, dry ice, and liquid nitrogen, and the temperature of the sample after quenching is not higher than room temperature.

7. The heat treatment process for obtaining an aluminum-magnesium-silicon alloy with high comprehensive performance according to claim 1, characterized in that: The composition of the aluminum-magnesium-silicon alloy includes the following components in mass percentage: Mg 1.0~1.4%; Si 1.0~1.4%; Cu0.05~0.15% Al allowance.

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