Aluminum alloy side wall profile by friction stir welding and application thereof

Abstract

This invention relates to the field of aluminum alloy profile technology, specifically to a friction stir welded aluminum alloy sidewall profile and its application. The chemical composition and mass percentage of the friction stir welded aluminum alloy sidewall profile are: Si: 0.66%–0.76%, Fe≤0.22%, Cu≤0.18%, Mn≤0.38%, Mg: 0.48%–0.58%, Cr≤0.25%, Zn≤0.10%, Ti≤0.10%, with the balance being Al and unavoidable impurities. The friction stir welded aluminum alloy sidewall profile is prepared from cast rods through a full-process, full-section isothermal extrusion, online solution treatment, tension stretching, and artificial aging. This invention addresses the higher dimensional accuracy requirements of friction stir welding on aluminum alloy materials. It employs high-strength molds and controls the deformation of the casting rod during production through isothermal extrusion and online solution treatment across the entire process and cross-section. This ensures that the width difference between the upper and lower sections of the welded joint of the final aluminum alloy profile is controlled within 0.3 mm, the thickness accuracy of the aluminum alloy profile can reach ±0.5 mm, and the height difference between the two aluminum alloy profiles is within 0.3 mm.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy profile technology, specifically to a friction stir welded aluminum alloy sidewall profile and its application. Background Technology

[0002] Due to its excellent extrudability, strength, weldability, and corrosion resistance, aluminum-magnesium-silicon alloys, 6005A alloy, are widely used in the manufacture of side wall profiles for subway trains. Currently, the cross-sections of 6005A alloy profiles are mostly arc-welded plug joints. When used as a side wall structural material, multiple profiles are welded together using metal inert gas (MIG) welding. The welding process requires filler wire and inert gas protection, generating spatter, fumes, and harmful radiation such as infrared or ultraviolet rays from the arc. Furthermore, defects such as porosity, cracks, and deformation are prone to occur at the weld seam, resulting in significant post-weld repair work. Additionally, the presence of weld seams increases the overall weight of the side wall structural components, affecting both strength and aesthetics.

[0003] Friction stir welding (FSW) was first invented by the Welding Institute in the UK in 1991. This technology utilizes the friction between a stirring head and the workpiece to soften the surrounding material and induce plastic deformation. Under the rotation of the stirring head, the softened material automatically fills the cavity formed behind the stirring pin, and the material is joined under the pressure of the stirring shoulder. Friction stir welded aluminum alloy sidewall profiles refer to aluminum alloy profiles with plug joints using friction stir welding. Compared to conventional 6005A alloy profiles with arc welding plug joints, its welding process does not require filler wire or inert gas protection; it only requires stirring kinetic energy, without melting. It is highly efficient, energy-saving, and a green and environmentally friendly welding method. The joint has little or no deformation, reducing post-weld repair work and losses. During welding, the weld metal undergoes plastic flow, preventing the formation of columnar crystal structures and refining grains. The welded joint exhibits excellent mechanical properties, particularly fatigue resistance, enhancing the strength and aesthetics of the vehicle body. With the rapid development of subway trains, research into friction stir welded aluminum alloy sidewall profiles has become an inevitable trend.

[0004] Therefore, how to produce aluminum alloy sidewall profiles for friction stir welding, and how to make the profiles have high strength, good weldability and fatigue resistance, while reducing production costs, is an urgent problem to be solved in the subway train industry at this stage. Summary of the Invention

[0005] To address the issues of high welding workload and impact on vehicle weight, strength, and aesthetics when using 6005A alloy MIG welded profiles, this invention provides a friction stir welded aluminum alloy sidewall profile and its application. To meet the higher dimensional accuracy requirements of friction stir welding on aluminum alloy materials, a high-strength mold is used. Through isothermal extrusion and online solution treatment throughout the entire process, the deformation of the cast rod during production is controlled, ensuring that the width difference between the upper and lower sections of the welded joint of the final aluminum alloy profile is controlled within 0.3mm, the thickness accuracy of the aluminum alloy profile can reach ±0.5mm, and the height difference between two aluminum alloy profiles is within 0.3mm.

[0006] In a first aspect, the present invention provides an aluminum alloy sidewall profile for friction stir welding, the chemical composition and mass percentage of which are as follows:

[0007] Si: 0.66%~0.76%, Fe≤0.22%, Cu≤0.18%, Mn≤0.38%, Mg: 0.48%~0.58%, Cr≤0.25%, Zn≤0.10%, Ti≤0.10%, with the balance being Al and unavoidable impurities; the width difference between the upper and lower sections of the welded joint of the friction stir welded aluminum alloy sidewall profile is within 0.3mm, the thickness accuracy reaches ±0.5mm, and the height difference between the two profiles is within 0.3mm;

[0008] The aluminum alloy sidewall profiles for friction stir welding are prepared from cast rods through a full-process, full-section isothermal extrusion, online solution treatment, tension stretching, and artificial aging. The full-process, full-section isothermal extrusion conditions are as follows:

[0009] The casting rod is subjected to gradient heating at a temperature of 500±5℃, so that the temperature difference between the head and tail of the casting rod is within 30℃. The heated casting rod is then extruded. The die used for extrusion is made of H13 steel. Before extrusion, the die is kept at 500±5℃ for 6 to 9 hours. The extrusion speed is 2.1m / min.

[0010] The conditions for online solution treatment are:

[0011] The extruded profiles are subjected to forced air cooling. The temperature of the profiles at the extrusion die opening is not lower than 510℃. The forced air cooling uses a 50KW fan with an air volume of over 90%.

[0012] Furthermore, the deformation under tension is 0.5% to 1.5%.

[0013] Furthermore, after tension stretching, profiles whose interface dimensions do not meet the requirements for friction stir welding are reshaped.

[0014] Furthermore, the artificial aging temperature is 175±5℃, and the holding time is 9 hours.

[0015] Furthermore, the casting temperature of the ingot is 690–720℃, the casting speed is 30–50 mm / min, and the casting cooling water flow rate is 110–150 m³ / min. 3 / h.

[0016] Furthermore, the casting rod is first homogenized and then rolled before extrusion. The homogenization temperature is 560±5℃ and the homogenization time is 12 hours.

[0017] Furthermore, the width of the friction stir welded aluminum alloy sidewall profile is 400-500mm.

[0018] Secondly, the present invention provides an application of the above-mentioned friction stir welded aluminum alloy sidewall profile in the manufacture of subway trains.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention achieves a high-precision aluminum alloy sidewall profile by controlling extrusion process conditions, meeting the requirements of friction stir welding. Specifically, an extrusion die made of high-strength H13 die steel is used to reduce deformation during extrusion and ensure minimal dimensional fluctuations. Gradient heating of the cast ingot, combined with temperature monitoring of the extrusion device, ensures temperature stability during the extrusion process. Meanwhile, online solution treatment affects the mechanical properties and dimensional accuracy of the aluminum alloy sidewall profile. High mechanical properties require a sufficiently fast cooling rate; however, the faster the cooling rate, the greater the residual stress and residual variables in the profile, making it more prone to deformation and compromising dimensional accuracy. This invention addresses the issue that during online solution treatment, product shape and gap dimensions are affected by differences in cooling rates at different parts, leading to defects such as uneven gaps, bending, and twisting. A specific high-speed air-cooling quenching process is determined, which, while achieving good mechanical properties, solves the problem of cooling deformation in the profile, particularly ensuring dimensional uniformity between the head and tail ends.

[0021] The aluminum alloy sidewall profile of the present invention has a non-proportional elongation strength of 230 MPa or more, a tensile strength of 275 MPa or more, and an elongation after fracture of 10% or more. The transverse properties of the extrusion weld position can reach more than 90% of those of the position without extrusion weld. At the same time, the present invention can simplify the process, improve production efficiency, shorten the production cycle, and reduce production costs, thus having significant economic benefits. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0023] Example 1

[0024] A friction stir welded aluminum alloy sidewall profile with a width of 500mm has the following chemical composition and mass percentage:

[0025] Si: 0.66%, Fe: 0.15%, Cu: 0.10%, Mn: 0.23%, Mg: 0.58%, Cr: 0.11%, Zn: 0.05%, Ti: 0.01%, balance being Al and unavoidable impurities.

[0026] The width difference between the upper and lower sections of the welded joint of the aluminum alloy sidewall profile is within 0.3mm, the thickness accuracy is ±0.5mm, and the height difference between the two profiles is within 0.3mm. The non-proportional elongation strength is 240MPa, the tensile strength is 278MPa, and the elongation after fracture is 11%, which meets the requirements of friction stir welding for the dimensional accuracy and mechanical properties of the profile. According to the test, the transverse properties of the extrusion weld position can reach more than 90% of those of the non-extrusion weld position, and it can be used in the manufacture of subway trains.

[0027] It is prepared according to the following method:

[0028] (1) After the raw materials were batched and smelted according to the specified ratio, a semi-continuous oil casting process was used to obtain a round cast rod with a diameter of 465 mm. The casting temperature was 700℃, the casting speed was 30 mm / min, and the casting cooling water flow rate was 115 m³ / min. 3 / h;

[0029] (2) Place the casting rod at 560±5℃ for 12 hours to homogenize it;

[0030] (3) The casting rod is machined with a 5mm layer, and the surface roughness Ra after machining is not less than 6.3μm;

[0031] (4) The casting rod is heated in a gradient at a temperature of 500±5℃, so that the temperature difference between the head and tail of the casting rod is within 30℃. The heated casting rod is then extruded. The die used for extrusion is made of H13 steel. Before extrusion, the die is kept at 500±5℃ for 6 hours. The extrusion speed is 2.1m / min.

[0032] (5) The extruded profile is subjected to online solution treatment by strong air cooling. The temperature of the profile at the extrusion die opening is controlled to be no less than 510℃. The strong air cooling uses a 50KW fan with an air volume of 90%.

[0033] (6) The profile is subjected to tension stretching treatment with a deformation of 0.5%. After tension stretching, the profile whose interface size does not meet the requirements of friction stir welding is shaped.

[0034] (7) The profile is subjected to artificial aging treatment at a temperature of 175±5℃ and a holding time of 9h.

[0035] Example 2

[0036] A friction stir welded aluminum alloy sidewall profile with a width of 500mm has the following chemical composition and mass percentage:

[0037] Si: 0.76%, Fe: 0.08%, Cu: 0.15%, Mn: 0.30%, Mg: 0.51%, Cr: 0.07%, Zn: 0.03%, Ti: 0.03%, balance being Al and unavoidable impurities.

[0038] The width difference between the upper and lower sections of the welded joint of the aluminum alloy sidewall profile is within 0.3mm, the thickness accuracy is ±0.5mm, and the height difference between the two profiles is within 0.3mm. The non-proportional elongation strength is 246MPa, the tensile strength is 288MPa, and the elongation after fracture is 11.5%, which meets the requirements of friction stir welding for the dimensional accuracy and mechanical properties of the profile. According to the test, the transverse properties of the extrusion weld position can reach more than 90% of those of the non-extrusion weld position, and it can be used in the manufacture of subway trains.

[0039] It is prepared according to the following method:

[0040] (1) After the raw materials were batched and smelted according to the specified ratio, a semi-continuous oil-lubricated casting method was used to obtain a round cast rod with a diameter of 465 mm. The casting temperature was 720℃, the casting speed was 50 mm / min, and the casting cooling water flow rate was 140 m³ / min. 3 / h;

[0041] (2) Place the casting rod at 560±5℃ for 12 hours to homogenize it;

[0042] (3) The casting rod is machined with a 5mm layer, and the surface roughness Ra after machining is not less than 6.3μm;

[0043] (4) The casting rod is heated in a gradient manner at a temperature of 500±5℃, so that the temperature difference between the head and tail of the casting rod is within 30℃. The heated casting rod is then extruded. The die used for extrusion is made of H13 steel. Before extrusion, the die is kept at 500±5℃ for 9 hours. The extrusion speed is 2.1m / min.

[0044] (5) The extruded profile is subjected to online solution treatment by strong air cooling. The temperature of the profile at the extrusion die opening is controlled to be no less than 510℃. The strong air cooling uses a 50KW fan with an air volume of 90%.

[0045] (6) The profile is subjected to tension stretching treatment with a deformation of 1.0%. After tension stretching, the profile whose insertion interface size does not meet the requirements of friction stir welding is shaped.

[0046] (7) The profile is subjected to artificial aging treatment at a temperature of 175±5℃ and a holding time of 9h.

[0047] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A friction stir welded aluminum alloy sidewall profile, characterized in that, The chemical composition and mass percentage are as follows: Si: 0.66%~0.76%, Fe≤0.22%, Cu≤0.18%, Mn≤0.38%, Mg: 0.48%~0.58%, Cr≤0.25%, Zn≤0.10%, Ti≤0.10%, with the balance being Al and unavoidable impurities; the width difference between the upper and lower sections of the welded joint of the friction stir welded aluminum alloy sidewall profile is within 0.3mm, the thickness accuracy reaches ±0.5mm, and the height difference between the two profiles is within 0.3mm; The aluminum alloy sidewall profiles for friction stir welding are prepared from cast rods through a full-process, full-section isothermal extrusion, online solution treatment, tension stretching, and artificial aging. The full-process, full-section isothermal extrusion conditions are as follows: The casting rod is subjected to gradient heating at a temperature of 500±5℃, so that the temperature difference between the head and tail of the casting rod is within 30℃. The heated casting rod is then extruded. The die used for extrusion is made of H13 steel. Before extrusion, the die is kept at 500±5℃ for 6~9 hours. The extrusion speed is 2.1m / min. The conditions for online solution treatment are: The extruded profiles are subjected to forced air cooling. The temperature of the profiles at the extrusion die opening is not lower than 510℃. The forced air cooling uses a 50KW fan with an air volume of over 90%. The deformation under tension is 0.5% to 1.5%.

2. The friction stir welded aluminum alloy sidewall profile as described in claim 1, characterized in that, After tension stretching, profiles whose interface dimensions do not meet the requirements for friction stir welding are reshaped.

3. The friction stir welded aluminum alloy sidewall profile as described in claim 1, characterized in that, The artificial aging temperature is 175±5℃, and the heat preservation time is 9h.

4. The friction stir welded aluminum alloy sidewall profile as described in claim 1, characterized in that, The casting temperature of the casting rod is 690~720℃, the casting speed is 30~50mm / min, and the casting cooling water flow rate is 110~150m³ / min. 3 / h.

5. The friction stir welded aluminum alloy sidewall profile as described in claim 1, characterized in that, Before extrusion, the cast rod is first homogenized and then rolled. The homogenization temperature is 560±5℃ and the homogenization time is 12 hours.

6. The friction stir welded aluminum alloy sidewall profile as described in claim 1, characterized in that, The width of the aluminum alloy sidewall profile for friction stir welding is 400~500mm.

7. The application of a friction stir welded aluminum alloy sidewall profile as described in any one of claims 1 to 6 in the manufacture of subway trains.