A heat treatment method to improve the strength and corrosion resistance of welded joints of 6xxx series aluminum alloy profiles

Abstract

This invention provides a heat treatment method for improving the strength and corrosion resistance of welded joints in 6xxx series aluminum alloy profiles, belonging to the field of aluminum alloy heat treatment technology. The heat treatment method provided by this invention includes the following steps: sequentially subjecting hot-extruded 6xxx series aluminum alloy profiles to online quenching, peak aging, welding, and post-weld low-temperature short-time annealing. This invention promotes the precipitation of nanoscale aluminide dispersed phases through low-temperature short-time annealing. These phases strongly pin dislocations and grain boundaries, producing substructure strengthening and direct precipitation strengthening effects, thus improving the strength of the welded joint. Furthermore, they alter the potential difference between the alloy matrix and the welded joint, improving the corrosion resistance of the welded joint. Results from the embodiments show that the strength of the welded joint obtained using the heat treatment method provided by this invention is 44–49 MPa higher than that obtained after conventional welding, while the erosion grade of the welded joint decreases from EB level to P level.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy heat treatment technology, and in particular to a heat treatment method for improving the strength and corrosion resistance of welded joints of 6xxx series aluminum alloy profiles. Background Technology

[0002] 6xxx series aluminum alloy profiles are key materials for achieving lightweight transportation. Their extensive use can reduce vehicle weight by 30-50%, manufacturing workload by 40%, and improve running, acceleration, safety, and comfort performance, thus achieving energy conservation and emission reduction. Existing 6xxx series aluminum alloys have high strength, good ductility and toughness, and excellent machinability. However, MIG welding presents problems such as low joint strength and poor joint corrosion resistance.

[0003] Currently, the main methods for improving the joint strength and corrosion resistance of MIG welds on 6xxx series aluminum alloy profiles are as follows: Adding a large amount of transition metals and rare earth microalloying elements to the alloy welding wire refines the grains at the weld joint, resulting in fine-grained strengthening and thus improving the joint strength. Simultaneously, utilizing the residual heat during welding to precipitate fine metastable strengthening phases during the cooling process improves the joint's corrosion resistance. While these methods can improve joint strength and corrosion resistance to some extent, the large amount of added microalloying elements can easily agglomerate in the alloy matrix due to improper manufacturing processes, forming coarse phases and failing to exert the beneficial effects of microalloying, thus negating the strengthening effect on the weld joint. Furthermore, for MIG welding, the manufacturing process of high-alloyed welding wire is complex and expensive, increasing material costs. Therefore, how to improve the joint strength and corrosion resistance of MIG welds on 6xxx series aluminum alloy profiles has become an urgent problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a heat treatment method for improving the strength and corrosion resistance of welded joints of 6xxx series aluminum alloy profiles. The heat treatment method provided by this invention can greatly improve the strength and corrosion resistance of welded joints of 6xxx series aluminum alloy profiles.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a heat treatment method for improving the strength and corrosion resistance of welded joints in 6xxx series aluminum alloy profiles, comprising the following steps:

[0007] Hot-extruded aluminum alloy profiles of the 6xxx series were subjected to online quenching, peak aging, welding, and post-weld low-temperature short-time annealing treatment in sequence to obtain welded joints of 6xxx series aluminum alloy profiles with high weldability.

[0008] Preferably, the 6xxx series aluminum alloy hot-extruded profile is obtained by hot extrusion of 6xxx series aluminum alloy; the extrusion ratio of the hot extrusion is 25 to 30.

[0009] Preferably, the 6xxx series aluminum alloy is an Al-Mg-Si-Mn-Cu-Sc-Zr aluminum alloy.

[0010] Preferably, the chemical composition of the 6xxx series aluminum alloy, by mass percentage, includes: Mg 0.62-0.70%, Si 0.75-0.85%, Mn 0.25-0.30%, Cu 0.15-0.20%, Sc 0.06-0.10%, Zr 0.05-0.08%, Ti 0.01-0.02%, Fe ≤0.13%, Zn ≤0.12%, and the balance Al.

[0011] Preferably, the online quenching temperature is 520–540°C.

[0012] Preferably, the cooling method for the online quenching is room temperature water mist quenching.

[0013] Preferably, the time from the extrusion exit to the start of online quenching and cooling for the 6xxx series aluminum alloy hot-extruded profile is less than 40 seconds.

[0014] Preferably, the peak aging temperature is 170–180°C, and the peak aging holding time is 12–16 h.

[0015] Preferably, the welding is MIG welding.

[0016] Preferably, the temperature of the post-weld low-temperature short-time annealing treatment is 320-340°C, the holding time of the post-weld low-temperature short-time annealing treatment is 0.5-2 hours, and the cooling method of the post-weld low-temperature short-time annealing treatment is natural cooling at room temperature.

[0017] This invention provides a heat treatment method to improve the strength and corrosion resistance of welded joints of 6xxx series aluminum alloy profiles, comprising the following steps: hot-extruded 6xxx series aluminum alloy profiles are sequentially subjected to online quenching, peak aging, welding, and post-weld low-temperature short-time annealing to obtain a high-weldability 6xxx series aluminum alloy profile welded joint. This invention first performs online quenching and peak aging on the hot-extruded alloy profiles, followed by welding. After cooling, the welded joint undergoes low-temperature short-time annealing, which promotes the precipitation of nano-sized aluminide dispersed phases in the welded joint. These nano-sized aluminide dispersed phases strongly pin dislocations and grain boundaries, producing substructure strengthening and direct precipitation strengthening effects, thus improving the strength of the welded joint. Furthermore, the fine and uniform dispersed phases formed by low-temperature short-time annealing can alter the potential difference between the alloy matrix and the welded joint, thereby improving the corrosion resistance of the welded joint. The results of the embodiments show that the strength of the welded joint obtained by the heat treatment method provided by the present invention is 44-49 MPa higher than that of the welded joint obtained by conventional welding. At the same time, the corrosion level of the welded joint is reduced from EB level to P level, indicating that the heat treatment method provided by the present invention can greatly improve the strength and corrosion resistance of the welded joint of 6xxx series aluminum alloy profiles. Attached Figure Description

[0018] Figure 1 This is a dimensional drawing of 6xxx series aluminum alloy hot-extruded profiles;

[0019] Figure 2 Transmission electron microscopy image of the welded joint of 6xxx series aluminum alloy profile obtained in Comparative Example 1;

[0020] Figure 3 The image shows the transmission electron microstructure of the welded joint of the 6xxx series aluminum alloy profile obtained in Example 1.

[0021] Figure 4 The image shows the exfoliation corrosion of the welded joint of the 6xxx series aluminum alloy profile obtained in Comparative Example 1.

[0022] Figure 5 This is a peeling corrosion diagram of the welded joint of the 6xxx series aluminum alloy profile obtained in Example 1. Detailed Implementation

[0023] This invention provides a heat treatment method for improving the strength and corrosion resistance of welded joints in 6xxx series aluminum alloy profiles, comprising the following steps:

[0024] Hot-extruded aluminum alloy profiles of the 6xxx series were subjected to online quenching, peak aging, welding, and post-weld low-temperature short-time annealing treatment in sequence to obtain welded joints of 6xxx series aluminum alloy profiles with high weldability.

[0025] The heat treatment method provided by this invention is applicable to 6xxx series aluminum alloys of any chemical composition. In this invention, the 6xxx series aluminum alloy hot-extruded profiles are preferably obtained by hot extrusion of 6xxx series aluminum alloys. In this invention, the dimensions of the 6xxx series aluminum alloy hot-extruded profiles are as follows: Figure 1 As shown.

[0026] In this invention, the 6xxx series aluminum alloy is preferably an Al-Mg-Si-Mn-Cu-Sc-Zr aluminum alloy. In this invention, the chemical composition of the 6xxx series aluminum alloy, by mass percentage, preferably includes: Mg 0.62-0.70%, Si 0.75-0.85%, Mn 0.25-0.30%, Cu 0.15-0.20%, Sc 0.06-0.10%, Zr 0.05-0.08%, Ti 0.01-0.02%, Fe ≤0.13%, Zn ≤0.12%, and the balance Al; more preferably: Mg 0.63-0.68%, Si 0.76-0.83%, Mn 0.26-0.29%, Cu 0.15-0.20%, Sc 0.06-0.10%, Zr 0.05-0.08%, Ti 0.01-0.02%, Fe ≤0.13%, Zn ≤0.12%, and the balance Al. In this invention, the content of a single impurity element in the 6xxx series aluminum alloy is preferably ≤0.05%, more preferably ≤0.03%; the total content of the impurity elements is preferably ≤0.15%, more preferably ≤0.12%. The 6xxx series aluminum alloy used in this invention has the characteristics of light weight and excellent mechanical properties.

[0027] The present invention does not have any special requirements on the specific source of the 6xxx series aluminum alloy. It can be any commercially available product known in the art or prepared by itself according to the above chemical composition.

[0028] In this invention, the extrusion ratio of the hot extrusion is preferably 25-30, more preferably 28. In this invention, the thickness of the 6xxx series aluminum alloy hot-extruded profile is preferably 1-4 mm, more preferably 2-3 mm.

[0029] In this invention, the online quenching temperature is preferably 520–540°C, more preferably 525–535°C, and even more preferably 530°C; the cooling method for the online quenching is preferably room temperature water mist quenching. This invention, by performing online quenching on hot-extruded 6xxx series aluminum alloy profiles, can fully dissolve alloying elements into the matrix, increasing the concentration of solute atoms in the solid solution to achieve a high artificial aging strengthening effect; the room temperature water mist quenching retains solute atoms and vacancies in the alloy matrix in a supersaturated form at room temperature during the solid solution process.

[0030] In this invention, the time from the extrusion exit to the start of online quenching and cooling of the 6xxx series aluminum alloy hot-extruded profile is preferably <40 seconds, more preferably <30 seconds, and even more preferably <20 seconds. By controlling the time from the extrusion exit to the start of online quenching and cooling of the aluminum alloy hot-extruded profile, this invention can avoid the adverse effects on the strengthening effect and corrosion resistance of the alloy welded joint caused by excessively long time intervals.

[0031] In this invention, the peak aging temperature is preferably 170–180°C, more preferably 175°C; the peak aging holding time is preferably 12–16 hours, more preferably 13–15 hours, and even more preferably 14 hours. This invention does not have special requirements for the specific operation of the peak aging; operations well-known to those skilled in the art can be used. By controlling the peak aging parameters, this invention can induce the precipitation of metastable strengthening phases in the alloy, thereby improving the matrix strength of the alloy profile.

[0032] In this invention, the welding is preferably MIG welding. This invention does not impose any special limitations on the specific operation of the MIG welding; the operation of MIG welding of 6xxx series aluminum alloys, which is well known to those skilled in the art, can be used. In this invention, when the 6xxx series aluminum alloy is an Al-Mg-Si-Mn-Cu-Sc-Zr aluminum alloy, the preferred process parameters for the MIG welding are: ER5087 aluminum alloy welding wire with a diameter of 3.0 mm, pure argon gas with a flow rate of 40 L / min, welding current of 230 A, voltage of 20 V, and welding speed of 360 mm / min.

[0033] In this invention, the temperature of the post-weld low-temperature short-time annealing treatment is preferably 320–340°C, more preferably 325–335°C, and even more preferably 330°C; the holding time of the post-weld low-temperature short-time annealing treatment is preferably 0.5–2 h, more preferably 1–1.5 h; and the cooling method of the post-weld low-temperature short-time annealing treatment is preferably natural cooling at room temperature. By controlling the parameters of the post-weld low-temperature short-time annealing treatment, this invention can effectively regulate the size, distribution, and quantity of nanoscale aluminum oxide dispersed phases in the alloy, causing them to precipitate finely and uniformly in the joint matrix. This facilitates substructure strengthening and direct precipitation strengthening after MIG welding, improving the joint strength and corrosion resistance of the alloy MIG welded joint.

[0034] This invention first performs online quenching and peak aging treatment on hot-extruded alloy profiles, followed by welding. After cooling, the welded joint undergoes low-temperature short-time annealing, which promotes the precipitation of nano-sized aluminide dispersed phases in the welded joint. On the one hand, the nano-sized aluminide dispersed phases strongly pin dislocations and grain boundaries, producing substructure strengthening and direct precipitation strengthening effects, thereby improving the strength of the welded joint. On the other hand, the fine and uniform dispersed phases formed by low-temperature short-time annealing can change the potential difference between the alloy matrix and the welded joint, thereby improving the corrosion resistance of the welded joint.

[0035] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0036] Example 1

[0037] A heat treatment method for improving the strength and corrosion resistance of welded joints in 6xxx series aluminum alloy profiles comprises the following steps:

[0038] 6xxx series aluminum alloy hot extruded profiles were sequentially subjected to online quenching, peak aging, welding, and post-weld low-temperature short-time annealing to obtain high weldability 6xxx series aluminum alloy profile welded joints.

[0039] The 6xxx series aluminum alloy hot-extruded profile is obtained by hot extrusion of 6xxx series aluminum alloy; the extrusion ratio of the hot extrusion is 28, and the thickness of the 6xxx series aluminum alloy hot-extruded profile is 2.0 mm;

[0040] The 6xxx series aluminum alloy is an Al-Mg-Si-Mn-Cu-Sc-Zr aluminum alloy; by mass percentage, the chemical composition of the 6xxx series aluminum alloy is: Mg 0.67%, Si 0.82%, Mn 0.28%, Cu 0.17%, Sc 0.06%, Zr 0.05%, Ti 0.01%, Fe 0.13%, Zn 0.02%, and the balance Al; the content of a single impurity element in the 6xxx series aluminum alloy is ≤0.03%, and the total content of impurity elements is ≤0.12%;

[0041] The online quenching temperature is 530℃, and the cooling method for online quenching is room temperature water mist quenching.

[0042] The time from the extrusion exit to the start of online quenching and cooling for the 6xxx series aluminum alloy hot-extruded profile is 30 seconds.

[0043] The peak aging temperature is 175℃, and the peak aging holding time is 14h.

[0044] The welding is MIG welding, and the process parameters of MIG welding are as follows: the welding wire is ER5087 aluminum alloy welding wire with a diameter of 3.0mm, the shielding gas is pure argon with a flow rate of 40L / min, the welding current is 230A, the voltage is 20V, and the welding speed is 360mm / min.

[0045] The temperature of the post-weld low-temperature short-time annealing treatment is 320℃, the holding time of the post-weld low-temperature short-time annealing treatment is 2h, and the cooling method of the post-weld low-temperature short-time annealing treatment is natural cooling at room temperature.

[0046] Example 2

[0047] The temperature of the post-weld low-temperature short-time annealing treatment is 340℃, and the holding time of the post-weld low-temperature short-time annealing treatment is 0.5h;

[0048] Other conditions are the same as in Example 1.

[0049] Example 3

[0050] The temperature of the post-weld low-temperature short-time annealing treatment is 330℃, and the holding time of the post-weld low-temperature short-time annealing treatment is 1 hour;

[0051] Other conditions are the same as in Example 1.

[0052] Comparative Example 1

[0053] The post-weld low-temperature short-time annealing process is omitted, and other conditions are the same as in Example 1.

[0054] Tensile properties and erosion tests were conducted on the welded joints of 6xxx series aluminum alloy profiles obtained in Examples 1-3 and Comparative Example 1, respectively. The testing standard for tensile properties was GB / T 228.1-2010, and the testing standard for erosion tests was GB / T22639-2008. The test results are shown in Table 1.

[0055] Table 1. Performance of welded joints of 6xxx series aluminum alloy profiles obtained in Examples 1-3 and Comparative Example 1.

[0056] Example Tensile strength / MPa Elongation / % Erosion level Comparative Example 1 193 5.8 EB Example 1 242 6.0 P Example 2 237 6.1 P Example 3 239 6.0 P

[0057] As can be seen from Table 1, compared with the 6xxx series aluminum alloy profile welded joints obtained without post-weld low-temperature short-time annealing treatment, the tensile strength of the 6xxx series aluminum alloy profile welded joints obtained by the heat treatment method provided by the present invention is increased by 44-49 MPa, and the erosion grade is reduced from EB grade to P grade. This indicates that the heat treatment method provided by the present invention effectively improves the strength and erosion resistance of the 6xxx series aluminum alloy profile welded joints.

[0058] Figure 2 The image shows the transmission electron microstructure of the welded joint of the 6xxx series aluminum alloy profile obtained in Comparative Example 1. Figure 3 This is a transmission electron micrograph of the welded joint of the 6xxx series aluminum alloy profile obtained in Example 1. Figure 2 and Figure 3 The comparison shows that the internally dispersed phase in the welded joint of 6xxx series aluminum alloy profiles obtained by the heat treatment method provided by this invention is fine and uniformly distributed. Figure 3 ), and the quantity is greater than that of dispersed phases in welded joints of 6xxx series aluminum alloy profiles that have not undergone post-weld low-temperature short-time annealing treatment. Figure 2 ).

[0059] Figure 4 This is a peeling corrosion image of the welded joint of the 6xxx series aluminum alloy profile obtained in Comparative Example 1. Figure 5 This is a peeling corrosion image of the welded joint of the 6xxx series aluminum alloy profile obtained in Example 1. Figure 4 and Figure 5 The comparison shows that the erosion resistance of the welded joints of 6xxx series aluminum alloy profiles obtained by the heat treatment method provided by this invention is superior. Figure 5 The erosion resistance of welded joints of 6xxx series aluminum alloy profiles obtained without post-weld low-temperature short-time annealing is better. Figure 4 ).

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A heat treatment method for improving the strength and corrosion resistance of welded joints of 6xxx series aluminum alloy profiles, comprising the following steps: 6xxx series aluminum alloy hot extruded profiles were sequentially subjected to online quenching, peak aging, welding, and post-weld low-temperature short-time annealing to obtain high weldability 6xxx series aluminum alloy profile welded joints. The 6xxx series aluminum alloy is an Al-Mg-Si-Mn-Cu-Sc-Zr aluminum alloy; the welding is MIG welding; the process parameters of the MIG welding are: the welding wire is ER5087 aluminum alloy welding wire with a diameter of 3.0mm, the shielding gas is pure argon with a flow rate of 40L / min, the welding current is 230A, the voltage is 20V, and the welding speed is 360mm / min. The temperature of the post-weld low-temperature short-time annealing treatment is 320~340℃, the holding time of the post-weld low-temperature short-time annealing treatment is 0.5~2h, and the cooling method of the post-weld low-temperature short-time annealing treatment is natural cooling at room temperature. The chemical composition of the 6xxx series aluminum alloy, by mass percentage, includes: Mg 0.62~0.70%, Si 0.75~0.85%, Mn 0.25~0.30%, Cu 0.15~0.20%, Sc 0.06~0.10%, Zr 0.05~0.08%, Ti 0.01~0.02%, Fe≤0.13%, Zn≤0.12%, and the balance Al.

2. The heat treatment method according to claim 1, characterized in that, The 6xxx series aluminum alloy hot-extruded profile is obtained by hot extrusion of 6xxx series aluminum alloy; the extrusion ratio of the hot extrusion is 25~30.

3. The heat treatment method according to claim 1, characterized in that, The online quenching temperature is 520~540℃.

4. The heat treatment method according to claim 1, characterized in that, The cooling method for the online quenching is room temperature water mist quenching.

5. The heat treatment method according to claim 1, characterized in that, The time from the extrusion exit to the start of online quenching and cooling for the 6xxx series aluminum alloy hot-extruded profiles is less than 40 seconds.

6. The heat treatment method according to claim 1, characterized in that, The peak aging temperature is 170~180℃, and the peak aging holding time is 12~16h.

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