Aluminum alloy part and preparation method thereof

Abstract

The invention provides an aluminum alloy part and a preparation method thereof, and relates to the technical field of aluminum alloy welding, and the preparation method comprises the following steps: a welding treatment step: carrying out friction stir welding treatment on an aluminum alloy plate to obtain a welded aluminum alloy plate; a machining treatment step: carrying out cold deformation machining treatment on the welded aluminum alloy plate to obtain a machined aluminum alloy plate; and heat treatment is conducted, specifically, the machined aluminum alloy plate is subjected to heat treatment, and the aluminum alloy part is obtained. According to the method, the aluminum alloy plate subjected to welding treatment is subjected to cold deformation machining treatment, a large number of dislocations are introduced into the weld joint, in the subsequent heat treatment process, the large number of dislocations are beneficial to nucleation in the subsequent recrystallization process, the nucleation rate is larger than the growth rate of the grain boundary, and therefore abnormal growth of grains is restrained.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy welding, and particularly relates to an aluminum alloy part and a preparation method thereof. Background Art

[0002] Age-hardened aluminum alloys (2xxx, 6xxx and 7xxx) are widely used in aviation, aerospace, automobile, machinery manufacturing, shipbuilding and chemical industries due to their high specific strength, specific stiffness and corrosion resistance. However, 2xxx and 7xxx series aluminum alloys are very sensitive to thermal cracks, and it is difficult to achieve high-quality connections using traditional fusion welding technology. 6xxx series aluminum alloys have good fusion welding performance, but defects such as pores and dendrites are difficult to avoid, and the plastic toughness is poor, which is difficult to improve even with post-weld heat treatment. As a solid-phase connection technology, friction stir welding (FSW) can effectively avoid various defects caused by fusion welding and is very suitable for the welding of age-hardened aluminum alloys.

[0003] During the FSW process of age-hardened aluminum alloy, the heat-affected zone is over-aged and is the area with the lowest hardness in the joint. Therefore, the strength of the age-hardened aluminum alloy FSW joint is significantly lower than that of the parent material. Through post-weld heat treatment such as T6 (solid solution + quenching + artificial aging) or T3 / T4 (solid solution + quenching + natural aging), age-hardened aluminum alloys can obtain optimal mechanical properties. Achieving the same strength of age-hardened aluminum alloy joints and parent materials through post-weld heat treatment is of great significance for lightweight manufacturing in key areas of my country.

[0004] However, the preparation of age-hardened FSW aluminum alloy thick plates (thickness ≥ 12 mm) to achieve equal strength joints faces the following difficulties: (1) Abnormal grain growth: After the aluminum alloy FSW joint is subjected to post-weld solution treatment, the grains in the weld core zone are prone to abnormal growth, resulting in a decrease in the hardness, strength and ductility of the aluminum alloy, as well as the deterioration of the forming performance and corrosion resistance of the aluminum alloy; (2) Continuously distributed "S" lines: The rotation speed during the FSW process is relatively low, resulting in a relatively small degree of plastic deformation. The original oxide scale on the original joint surface of the workpiece is broken into many fine oxide particles after plastic deformation and redistributed in the joint in an S shape, which is called the "S" line. The continuous and obvious distribution of the "S" line will weaken the joint strength. During the post-weld heat treatment process, cracking along the "S" line is likely to occur, further weakening the joint strength. Summary of the invention

[0005] Therefore, the present invention provides an aluminum alloy part and a preparation method thereof, which can solve the technical problem of abnormal grain growth in the aging-strengthened aluminum alloy thick plate joint in the prior art.

[0006] In order to solve the above problems, the present invention provides a method for preparing an aluminum alloy part, comprising the following steps:

[0007] Welding process step: performing friction stir welding on the aluminum alloy plate to obtain a welded aluminum alloy plate;

[0008] Processing step: performing cold deformation processing on the welded joints of the aluminum alloy plate to obtain a processed aluminum alloy plate;

[0009] Heat treatment step: heat treating the processed aluminum alloy plate to obtain the aluminum alloy part.

[0010] Furthermore, in the welding process step: the thickness of the aluminum alloy plate is ≥12 mm.

[0011] Further, a friction stir welding process is performed on the aluminum alloy plate in multiple passes by using a friction stir welding tool; preferably, the friction stir welding tool comprises a stirring head and a stirring needle; and / or

[0012] The friction stir welding process adopts one of double-shoulder friction stir welding, differential friction stir welding, and static shoulder friction stir welding; and / or

[0013] The friction stir welding process has a welding speed of 0.5 to 2000 mm / min; and / or

[0014] Each time a friction stir welding process is added, the stirring needle is offset to the backward side, and the offset distance is 0 to 0.5 times the root diameter of the stirring needle.

[0015] Furthermore, the shape of the stirring head is cylindrical or conical; and / or

[0016] The material of the stirring head is one of tool steel, high temperature alloy, tungsten alloy and ceramic material; and / or

[0017] The rotation speed of the stirring head is 50-5000 r / min, the axial pressure is 2.0-200.0 kN, and the inclination angle of the stirring head is 0-3°; and / or

[0018] The shoulder diameter of the stirring head is 15 to 60 mm.

[0019] Furthermore, the end of the stirring needle is flat or spherical; and / or

[0020] The surface of the stirring needle is smooth, or the surface of the stirring needle has an annular groove or a thread; and / or

[0021] The length of the stirring needle is 1 to 100 mm; and / or

[0022] The root diameter of the stirring needle is 3 to 30 mm, and the end diameter is 2 to 30 mm.

[0023] Furthermore, in the processing: the cold deformation processing adopts one of stretching, extrusion, rolling and stamping; and / or

[0024] The total deformation amount of the cold deformation process is ≥10%.

[0025] Furthermore, in the heat treatment step: the heat treatment adopts T6 heat treatment;

[0026] Preferably, the T6 heat treatment includes solution treatment, quenching treatment and artificial aging treatment performed in sequence; further preferably, the temperature of the solution treatment is 450-540°C, and the time of the solution treatment is 0.2-10h; preferably, the temperature of the artificial aging treatment is 110-185°C, and the time of the artificial aging treatment is 8-24h.

[0027] Furthermore, before the welding step, the method further includes: performing surface treatment on the aluminum alloy plate;

[0028] Preferably, the surface treatment includes removing the surface oxide film and performing surface cleaning;

[0029] More preferably, the surface is cleaned using a dry cloth dipped in acetone or ethanol.

[0030] On the other hand, the present invention provides an aluminum alloy part, which is a welded aluminum alloy part; the aluminum alloy part is a welded aluminum alloy part; the grain size at the weld nugget of the joint of the aluminum alloy part is 1 to 20 μm; and no S line is observed in the aluminum alloy part.

[0031] Furthermore, the tensile strength and elongation of the joint of the aluminum alloy piece are not less than 97% of the aluminum alloy plate before welding;

[0032] Preferably, the aluminum alloy part is obtained by any of the preparation methods described above.

[0033] Compared with the prior art, the present invention has at least the following beneficial effects:

[0034] 1. On the one hand, the present invention provides a method for preparing an aluminum alloy part, which is obtained by performing stir friction welding on an aluminum alloy plate, then performing cold deformation processing on the weld joint, and then performing heat treatment; based on the above method, a large number of dislocations are introduced into the weld by performing cold deformation processing on the weld joint, and in the subsequent heat treatment process, the large number of dislocations are conducive to the nucleation of the subsequent recrystallization process, so that the nucleation rate is greater than the growth rate of the grain boundary, thereby inhibiting the abnormal growth of grains.

[0035] 2. Furthermore, the present invention performs multiple friction stir welding processes on the aluminum alloy plate, especially for the aluminum alloy thick plate, to produce a large degree of plastic deformation in the weld, which can fully disperse the "S" line, so that the oxide film particle size on the "S" line becomes smaller and the distribution is more dispersed; thereby avoiding "S" line cracking during cold deformation processing and post-weld heat treatment, and ensuring the strength of the weld joint.

[0036] 3. On the other hand, the present invention provides an aluminum alloy part obtained by the above-mentioned preparation method, wherein the grain size of the weld core zone of the joint of the aluminum alloy part is 1 to 20 μm; no "S" line is observed at the joint of the aluminum alloy part; the tensile strength and elongation at the joint of the aluminum alloy part are not less than 97% of the base material in the same heat treatment state, thereby ensuring that the obtained joint has better properties such as hardness, strength and ductility. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0038] Figure 1 A schematic flow chart of a method for preparing an aluminum alloy part of the present invention;

[0039] Figure 2 It is a cross-sectional microstructure diagram of the aluminum alloy plate joint and the aluminum alloy part joint in Example 1 of the present invention; wherein: (a) the "S" line distribution at the aluminum alloy plate joint, (b) the microstructure at the aluminum alloy plate joint, (c) the macromorphology at the aluminum alloy plate joint (welded FSW joint); (d) the macromorphology at the aluminum alloy part joint (equi-strength FSW joint), (e) the weld nugget microstructure at the aluminum alloy part joint, and (f) the microstructure of the base material;

[0040] Figure 3 is the tensile curve at the joint of the base material and the aluminum alloy plate in each embodiment and comparative example of the present invention;

[0041] Figure 4 It is the cross-sectional structure of the aluminum alloy plate joint and the aluminum alloy part joint in Comparative Example 1 of the present invention; wherein: (a) the "S" line distribution at the aluminum alloy plate joint, (b) is the microstructure at the aluminum alloy plate joint, (c) is the macroscopic morphology at the aluminum alloy plate joint (single-pass FSW welded joint); (d) is the macroscopic morphology at the aluminum alloy part joint (single-pass FSW+T6 joint);

[0042] Figure 5This is the cross-sectional macroscopic morphology of the joint of the aluminum alloy part in Comparative Example 2 of the present invention;

[0043] Figure 6 is the cross-sectional macroscopic morphology of the joint of the aluminum alloy part in Example 2 of the present invention;

[0044] Figure 7 This is the cross-sectional macroscopic morphology of the joint of the aluminum alloy part in Comparative Example 3 of the present invention; DETAILED DESCRIPTION

[0045] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0046] The present invention provides a method for preparing an aluminum alloy part. The method adopts the FSW method to perform multiple passes of welding on an age-strengthened aluminum alloy thick plate, produces a large degree of plastic deformation in the weld, fully disperses the "S" line, and makes the oxide film particle size on the "S" line become finer and more dispersed; at the same time, after welding, the joint is cold-deformed to introduce a large number of dislocations in the weld. In the subsequent post-weld solution heat treatment process, a large number of dislocations are conducive to the nucleation of the subsequent recrystallization process. When the nucleation rate is greater than the growth rate of the grain boundary, the abnormal growth of the grains will be suppressed. In addition, the process of the present invention is simple, has strong applicability, can be automatically produced, and is suitable for industrial promotion and application.

[0047] The scheme of the present invention is mainly as follows:

[0048] The present invention provides a method for preparing an aluminum alloy part, comprising the following steps:

[0049] Welding treatment step: removing the surface oxide film of the aluminum alloy plate to be welded and cleaning the surface, and then using a stir friction tool to perform multiple stir friction welding processes on the aluminum alloy plate to obtain a welded aluminum alloy plate;

[0050] The thickness of the aluminum alloy plate to be welded is ≥12mm; the friction stir tool includes a stirring head and a stirring needle; each time a friction stir welding process is added, the stirring needle is offset to the retreat side, and the offset distance is 0 to 0.5 times the root diameter of the stirring needle; since the "S" line is mainly biased toward the retreat side of the weld, the displacement of the stirring needle to the retreat side can expand the distribution area of ​​the "S" line and help to disperse the "S" line; the surface oxide film of the aluminum alloy plate to be welded is removed by mechanical grinding; the oil stain on the surface of the aluminum alloy plate to be welded is cleaned with dry cloth dipped in acetone or ethanol (i.e., surface cleaning);

[0051] Processing step: performing cold deformation processing on the aluminum alloy plate after welding to obtain the processed aluminum alloy plate;

[0052] Among them, the cold deformation processing adopts one of stretching, extrusion, rolling and stamping; the total deformation amount of the cold deformation processing is ≥10%; the cold deformation processing direction can be along the horizontal or longitudinal direction of the aluminum alloy plate after welding, and single cold deformation or multiple cold deformation is possible;

[0053] Heat treatment step: performing T6 heat treatment on the processed aluminum alloy plate to obtain an aluminum alloy part; wherein the T6 heat treatment includes solution treatment, quenching treatment, and artificial aging treatment performed in sequence; the temperature of the solution treatment is 450-540°C, and the time of the solution treatment is 0.2-10h; preferably, the temperature of the artificial aging treatment is 110-185°C, and the time of the artificial aging treatment is 8-24h.

[0054] Based on the above method, by performing multiple friction stir welding processes on the aluminum alloy plate, especially for the aluminum alloy thick plate, a large degree of plastic deformation is generated in the weld, which can fully disperse the "S" line, so that the oxide film particle size on the "S" line becomes smaller and the distribution is more dispersed; by performing cold deformation processing on the aluminum alloy plate after welding, a large number of dislocations are introduced into the weld. In the subsequent heat treatment process, a large number of dislocations are conducive to the nucleation of the subsequent recrystallization process, so that the nucleation rate is greater than the growth rate of the grain boundary, thereby inhibiting the abnormal growth of grains.

[0055] In some embodiments, the friction stir welding process adopts one of double-shoulder friction stir welding, differential friction stir welding, and static shoulder friction stir welding; the welding speed of the friction stir welding process is 0.5 to 2000 mm / min.

[0056] In some embodiments, the shape of the stirring head is cylindrical or conical; the material of the stirring head is one of tool steel, high-temperature alloy, tungsten alloy, and ceramic material; the rotation speed of the stirring head is 50 to 5000 r / min, the axial pressure is 2.0 to 200.0 kN, and the inclination angle of the stirring head is 0 to 3°; the shoulder diameter of the stirring head is 15 to 60 mm.

[0057] In some embodiments, the end of the stirring needle is flat or spherical; the surface of the stirring needle is smooth, or the surface of the stirring needle has annular grooves or threads; the side surface of the stirring needle is processed or not processed; the length of the stirring needle is 1 to 100 mm; the root diameter of the stirring needle is 3 to 30 mm, and the diameter of the end is 2 to 30 mm.

[0058] On the other hand, the present invention provides an aluminum alloy part, which is a welded aluminum alloy part; the grain size at the weld nugget of the joint of the aluminum alloy part is 1 to 20 μm; and no obvious "S" line (S line) is observed at the joint of the aluminum alloy part.

[0059] Furthermore, the tensile strength and elongation of the joints of the aluminum alloy parts are not less than 97% of the aluminum alloy plates before welding.

[0060] The aluminum alloy part is obtained by any of the preparation methods described above.

[0061] The present invention is further described below through specific examples and comparative examples, wherein the aluminum alloy sheet to be welded (ie, the parent material) has a tensile strength of about 453 MPa and an elongation of 14%.

[0062] Example 1

[0063] This embodiment provides a method for preparing an aluminum alloy part, such as Figure 1 As shown, the following steps are included:

[0064] Welding process steps: removing the surface oxide film of the aluminum alloy plate to be welded and cleaning the surface, then butting the aluminum alloy plate to be welded, and then fixing the aluminum alloy plate to be welded on a workbench, and performing a double-sided three-pass friction stir welding (FSW) process on the aluminum alloy plate with a friction stir tool to obtain a welded aluminum alloy plate;

[0065] The aluminum alloy plate to be welded is a 2219-T8 aluminum alloy rolled plate with a thickness of 28 mm; the surface oxide film of the aluminum alloy plate to be welded is removed by mechanical grinding; the oil stain on the surface of the aluminum alloy plate to be welded is cleaned by using dry cloth dipped in acetone (i.e., surface cleaning);

[0066] Among them, in the first pass FSW and the second pass FSW: the material of the stirring head is H13 steel, the stirring head is a concave shoulder, and the diameter of the concave shoulder is 24mm; the surface of the conical stirring needle has a right-hand thread, the root diameter of the stirring needle is 11mm, the diameter of the end is 6mm, and the needle length of the stirring needle is 12mm; the welding process parameters are: rotation speed 600rpm, welding speed 50mm / min, axial pressure of the stirring head is 35KN; in the second pass FSW, the distance that the stirring needle deviates to the backward side is 0.1 times the diameter of the stirring needle (i.e. 1.1mm);

[0067] In the third FSW, the stirring head is made of H13 steel, the stirring head has a concave shoulder, and the diameter of the concave shoulder is 30 mm; the surface of the conical stirring needle has a right-hand thread, the root diameter of the stirring needle is 14 mm, the end diameter is 8 mm, and the needle length of the stirring needle is 15 mm; the welding process parameters are: rotation speed 400 rpm, welding speed 100 mm / min, and axial pressure of the stirring head is 32 KN; compared with the second FSW, in the third FSW, the distance that the stirring needle deviates to the backward side is 0.1 times the diameter of the stirring needle (i.e., 1.4 mm);

[0068] Processing step: cold rolling the aluminum alloy plate after welding to obtain the aluminum alloy plate after welding; wherein the cold rolling is performed along the longitudinal direction of the aluminum alloy plate after welding (i.e., the thickness direction of the plate), and the deformation amount of the cold rolling is 20%;

[0069] Heat treatment step: performing T6 heat treatment on the processed aluminum alloy plate to obtain an aluminum alloy part; wherein the T6 heat treatment sequentially includes solution treatment at 535°C for 2 hours, followed by quenching, and finally artificial aging treatment at 170°C for 16 hours.

[0070] The organization and tensile curve of the joint prepared by the method of this embodiment are as follows: Figure 2 and 3 As shown in the figure, it can be seen that due to the three-pass friction stir welding process, the weld core is severely deformed, resulting in a more dispersed distribution of the "S" line, and the "S" line becomes less obvious and difficult to observe (see Figure 2 a); After three passes of friction stir welding, the average grain size of the weld nugget at the joint of the aluminum alloy plate after welding is about 10μm (see Figure 2 b), the tensile strength of the joint of the aluminum alloy plate after welding is 254MPa ( Figure 3 Column chart -I); by cold rolling 20% ​​deformation after welding, a large number of dislocations are introduced. In the subsequent solution heat treatment process, a large number of dislocations become nucleation points, which inhibit the abnormal growth of grains, and finally obtain strong FSW joints such as 2219-T8 aluminum alloy (see Figure 2 d).

[0071] The average grain size of the weld nugget at the joint of the aluminum alloy part of this embodiment is about 50 μm (see Figure 2 e), slightly smaller than the average grain size of the 2219-T8 aluminum alloy base material (i.e., the aluminum alloy plate to be welded) ( Figure 2 f), indicating that the weld nugget has not experienced abnormal grain growth; the tensile strength of the joint of the aluminum alloy part is about 455MPa, and the elongation is 14.5% ( Figure 3 Column II), the same as the parent material (tensile strength is about 453MPa, elongation is 14%, see Figure 3Column chart - parent material).

[0072] In summary, the method of this embodiment can be used to prepare an aged aluminum alloy FSW joint (i.e., a joint of an aluminum alloy part) that has no abnormal grain growth, no obvious "S" line, and is as strong as the parent material.

[0073] The above-mentioned embodiment 1 is a preferred embodiment adopting the necessary features and preferred technical features of the present invention, and the following embodiments are embodiments adopting the necessary features and non-preferred technical features.

[0074] Example 2

[0075] This embodiment provides a method for preparing an aluminum alloy part, comprising the following steps:

[0076] Welding process steps: removing the surface oxide film of the aluminum alloy plate to be welded and cleaning the surface, then butting the aluminum alloy plate to be welded, and then fixing the aluminum alloy plate to be welded on a workbench, and performing double-sided single-pass friction stir welding (FSW) on the aluminum alloy plate with a friction stir tool to obtain a welded aluminum alloy plate;

[0077] The aluminum alloy plate to be welded is a 2219-T8 aluminum alloy rolled plate with a thickness of 28 mm; the surface oxide film of the aluminum alloy plate to be welded is removed by mechanical grinding; the oil stain on the surface of the aluminum alloy plate to be welded is cleaned by using dry cloth dipped in acetone (i.e., surface cleaning);

[0078] The material of the stirring head is H13 steel, the stirring head has a concave shoulder, and the diameter of the concave shoulder is 30mm; the surface of the conical stirring needle has a right-hand thread, the root diameter of the stirring needle is 14mm, the diameter of the end is 8mm, and the needle length of the stirring needle is 15mm; the welding process parameters are: rotation speed 400rpm, welding speed 100mm / min, and axial pressure of the stirring head is 35KN;

[0079] Processing step: cold rolling the aluminum alloy plate after welding to obtain the aluminum alloy plate after welding; wherein the cold rolling is performed along the longitudinal direction of the aluminum alloy plate after welding (i.e., the thickness direction of the plate), and the deformation amount of the cold rolling is 20%;

[0080] Heat treatment step: performing T6 heat treatment on the processed aluminum alloy plate to obtain an aluminum alloy part; wherein the T6 heat treatment sequentially includes solution treatment at 535°C for 2 hours, followed by quenching, and finally artificial aging treatment at 170°C for 16 hours.

[0081] The structure of the aluminum alloy part prepared by the method of this embodiment is as follows: Figure 6As shown in the figure, it can be seen that the aluminum alloy part has no abnormal grain growth, but because the welding process is a single pass, the "S" line dispersion effect is poor, which greatly weakens the strength of the aluminum alloy part. The tensile strength of the joint of the aluminum alloy part is 401MPa, and the elongation is only 11.7% ( Figure 3 Column-III), which is much lower than that of parent material.

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing an aluminum alloy part, comprising the following steps:

[0084] Welding process steps: removing the surface oxide film of the aluminum alloy plate to be welded and cleaning the surface, then butting the aluminum alloy plate to be welded, and then fixing the aluminum alloy plate to be welded on a workbench, and performing double-sided single-pass friction stir welding (FSW) on the aluminum alloy plate with a friction stir tool to obtain a welded aluminum alloy plate;

[0085] The aluminum alloy plate to be welded is a 2219-T8 aluminum alloy rolled plate with a thickness of 28 mm; the surface oxide film of the aluminum alloy plate to be welded is removed by mechanical grinding; the oil stain on the surface of the aluminum alloy plate to be welded is cleaned by using dry cloth dipped in acetone (i.e., surface cleaning);

[0086] The material of the stirring head is H13 steel, the stirring head has a concave shoulder, and the diameter of the concave shoulder is 30mm; the surface of the conical stirring needle has a right-hand thread, the root diameter of the stirring needle is 14mm, the diameter of the end is 8mm, and the needle length of the stirring needle is 15mm; the welding process parameters are: rotation speed 400rpm, welding speed 100mm / min, and axial pressure of the stirring head is 35KN;

[0087] Heat treatment step: performing T6 heat treatment on the aluminum alloy plate after the above welding treatment to obtain an aluminum alloy part; wherein the T6 heat treatment sequentially includes solution treatment at 535°C for 2 hours, followed by quenching, and finally artificial aging treatment at 170°C for 16 hours.

[0088] The microstructure and tensile curve of the aluminum alloy parts prepared by the comparative example method are as follows: Figure 4 and 3 As shown in Figure 2, it can be seen that since the welding process is a single pass, after the welding process, the "S" line is poorly dispersed and the "S" line is easier to observe (see Figure 2). Figure 4 a), the average grain size of the weld nugget of the aluminum alloy plate after welding is about 20μm (see Figure 4 b); During the subsequent solution heat treatment, the weld nugget undergoes obvious abnormal grain growth (see Figure 4d), the grain size of the obtained aluminum alloy part is much larger than the average grain size of the weld nugget and the parent material of the aluminum alloy plate after welding (50 μm in width and 200-300 μm in length).

[0089] Compared with the embodiment, the comparative example adopts a single-pass friction stir treatment, resulting in a continuously distributed "S" line of the weld nugget. Since no cold deformation processing is performed, abnormally coarse grains are formed during the heat treatment process. The mechanical properties of the joint obtained by single-pass FSW+T6 after welding are greatly weakened, resulting in fracture along the weld nugget "S" line during the tensile process of the joint. The tensile strength of the joint of the aluminum alloy part is only 369MPa, and the elongation is 8% ( Figure 3 Column IV), which is much lower than the strength of 2219-T8 aluminum alloy parent material and only slightly higher than the strength of aluminum alloy plate after single-pass FSW welding ( Figure 5 Curve II).

[0090] Comparative Example 2

[0091] This comparative example provides a method for preparing an aluminum alloy part, comprising the following steps:

[0092] Welding process steps: removing the surface oxide film of the aluminum alloy plate to be welded and cleaning the surface, then butting the aluminum alloy plate to be welded, and then fixing the aluminum alloy plate to be welded on a workbench, and performing a double-sided three-pass friction stir welding (FSW) process on the aluminum alloy plate with a friction stir tool to obtain a welded aluminum alloy plate;

[0093] The aluminum alloy plate to be welded is a 2219-T8 aluminum alloy rolled plate with a thickness of 28 mm; the surface oxide film of the aluminum alloy plate to be welded is removed by mechanical grinding; the oil stain on the surface of the aluminum alloy plate to be welded is cleaned by using dry cloth dipped in acetone (i.e., surface cleaning);

[0094] Among them, in the first pass FSW and the second pass FSW: the material of the stirring head is H13 steel, the stirring head is a concave shoulder, and the diameter of the concave shoulder is 24mm; the surface of the conical stirring needle has a right-hand thread, the root diameter of the stirring needle is 11mm, the diameter of the end is 6mm, and the needle length of the stirring needle is 12mm; the welding process parameters are: rotation speed 600rpm, welding speed 50mm / min, axial pressure of the stirring head is 35KN; in the second pass FSW, the distance that the stirring needle deviates to the backward side is 0.1 times the diameter of the stirring needle (i.e. 1.1mm);

[0095] In the third FSW, the material of the stirring head is H13 steel, the stirring head is a concave shoulder, and the diameter of the concave shoulder is 30 mm; the surface of the conical stirring needle has a right-hand thread, the root diameter of the stirring needle is 14 mm, the end diameter is 8 mm, and the needle length of the stirring needle is 15 mm; the welding process parameters are: rotation speed 400 rpm, welding speed 100 mm / min, and axial pressure of the stirring head is 32 KN; compared with the second FSW, in the third FSW, the distance that the stirring needle deviates to the backward side is 0.3 times the diameter of the stirring needle (i.e., 4.2 mm);

[0096] Heat treatment step: performing T6 heat treatment on the aluminum alloy plate after the above welding treatment to obtain an aluminum alloy part; wherein the T6 heat treatment sequentially includes solution treatment at 535°C for 2 hours, followed by quenching, and finally artificial aging treatment at 170°C for 16 hours.

[0097] The structure of the aluminum alloy part prepared by the comparative example method is as follows: Figure 5 As shown in the figure, it can be seen that since no cold deformation processing is performed, a large number of dislocations cannot be introduced, and the grain abnormality during the solid solution process cannot be suppressed, resulting in poor plasticity and tensile strength. The tensile strength of the obtained aluminum alloy joint is 398MPa, and the elongation is only 11.3% ( Figure 3 Column-V), which is much lower than the parent material.

[0098] Comparative Example 3

[0099] This comparative example provides a method for preparing an aluminum alloy part, comprising the following steps:

[0100] Welding process steps: removing the surface oxide film of the aluminum alloy plate to be welded and cleaning the surface, then butting the aluminum alloy plate to be welded, and then fixing the aluminum alloy plate to be welded on a workbench, and performing a double-sided three-pass friction stir welding (FSW) process on the aluminum alloy plate with a friction stir tool to obtain a welded aluminum alloy plate;

[0101] The aluminum alloy plate to be welded is a 2219-T8 aluminum alloy rolled plate with a thickness of 28 mm; the surface oxide film of the aluminum alloy plate to be welded is removed by mechanical grinding; the oil stain on the surface of the aluminum alloy plate to be welded is cleaned by using dry cloth dipped in acetone (i.e., surface cleaning);

[0102] Among them, in the first pass FSW and the second pass FSW: the material of the stirring head is H13 steel, the stirring head is a concave shoulder, and the diameter of the concave shoulder is 24mm; the surface of the conical stirring needle has a right-hand thread, the root diameter of the stirring needle is 11mm, the diameter of the end is 6mm, and the needle length of the stirring needle is 12mm; the welding process parameters are: rotation speed 600rpm, welding speed 50mm / min, axial pressure of the stirring head is 35KN; in the second pass FSW, the distance that the stirring needle deviates to the backward side is 0.1 times the diameter of the stirring needle (i.e. 1.1mm);

[0103] In the third FSW, the material of the stirring head is H13 steel, the stirring head is a concave shoulder, and the diameter of the concave shoulder is 30 mm; the surface of the conical stirring needle has a right-hand thread, the root diameter of the stirring needle is 14 mm, the end diameter is 8 mm, and the needle length of the stirring needle is 15 mm; the welding process parameters are: rotation speed 400 rpm, welding speed 100 mm / min, and axial pressure of the stirring head is 32 KN; compared with the second FSW, in the third FSW, the distance that the stirring needle deviates to the backward side is 0.3 times the diameter of the stirring needle (i.e., 4.2 mm);

[0104] Processing step: cold rolling the aluminum alloy plate after welding to obtain the aluminum alloy plate after welding; wherein the cold rolling is performed along the longitudinal direction of the aluminum alloy plate after welding (i.e., the thickness direction of the plate), and the deformation amount of the cold rolling is 5%;

[0105] Heat treatment step: performing T6 heat treatment on the processed aluminum alloy plate to obtain an aluminum alloy part; wherein the T6 heat treatment sequentially includes solution treatment at 535°C for 2 hours, followed by quenching, and finally artificial aging treatment at 170°C for 16 hours.

[0106] The structure of the aluminum alloy part prepared by the comparative example method is as follows: Figure 7 As shown in the figure, it can be seen that due to the insufficient deformation of the joint cold deformation processing, the obtained aluminum alloy part has undergone significant abnormal grain growth; the abnormally coarse grains seriously reduce the plasticity and tensile strength of the aluminum alloy part. The tensile strength of the joint of the aluminum alloy part of this comparative example is 398MPa, and the elongation is only 6.2% ( Figure 3 Bar-VI), which is much lower than that of the parent material.

[0107] It is easy for those skilled in the art to understand that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present invention. These improvements and variations should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing an aluminum alloy part, characterized in that: The following steps are involved: Welding process step: performing friction stir welding on the aluminum alloy plate to obtain a welded aluminum alloy plate; Processing step: performing cold deformation processing on the welded joints of the aluminum alloy plate to obtain a processed aluminum alloy plate; Heat treatment step: heat treating the processed aluminum alloy plate to obtain the aluminum alloy part.

2. The method for preparing an aluminum alloy part according to claim 1, characterized in that: In the welding process step: the thickness of the aluminum alloy plate is ≥12 mm.

3. The method for preparing an aluminum alloy part according to claim 1, characterized in that: A friction stir welding process is performed on the aluminum alloy plate by using a friction stir welding tool; preferably, the friction stir welding tool comprises a stirring head and a stirring needle; and / or The friction stir welding process adopts one of double-shoulder friction stir welding, differential friction stir welding, and static shoulder friction stir welding; and / or The friction stir welding process has a welding speed of 0.5 to 2000 mm / min; and / or Each time a friction stir welding process is added, the stirring needle is offset to the backward side, and the offset distance is 0 to 0.5 times the root diameter of the stirring needle.

4. The method for preparing an aluminum alloy part according to claim 3, characterized in that: The shape of the stirring head is cylindrical or conical; and / or The material of the stirring head is one of tool steel, high temperature alloy, tungsten alloy and ceramic material; and / or The rotation speed of the stirring head is 50-5000 r / min, the axial pressure is 2.0-200.0 kN, and the inclination angle of the stirring head is 0-3°; and / or The shoulder diameter of the stirring head is 15 to 60 mm.

5. The method for preparing an aluminum alloy part according to claim 3, characterized in that: The end of the stirring needle is flat or spherical; and / or The surface of the stirring needle is smooth, or the surface of the stirring needle has an annular groove or a thread; and / or The length of the stirring needle is 1 to 100 mm; and / or The root diameter of the stirring needle is 3 to 30 mm, and the end diameter is 2 to 30 mm.

6. The method for preparing an aluminum alloy part according to claim 1, characterized in that: In the processing: the cold deformation processing adopts one of stretching, extrusion, rolling and stamping; and / or The total deformation amount of the cold deformation process is ≥10%.

7. The method for preparing an aluminum alloy part according to claim 1, characterized in that: In the heat treatment step: the heat treatment adopts T6 heat treatment; Preferably, the T6 heat treatment includes solution treatment, quenching treatment and artificial aging treatment performed in sequence; further preferably, the temperature of the solution treatment is 450-540°C, and the time of the solution treatment is 0.2-10h; preferably, the temperature of the artificial aging treatment is 110-185°C, and the time of the artificial aging treatment is 8-24h.

8. The method for preparing an aluminum alloy part according to claim 1, characterized in that: Before the welding process, the method further includes: performing surface treatment on the aluminum alloy plate; Preferably, the surface treatment includes removing the surface oxide film and performing surface cleaning; More preferably, the surface is cleaned using a dry cloth dipped in acetone or ethanol.

9. An aluminum alloy part, characterized in that: The aluminum alloy part is a welded aluminum alloy part; the grain size at the weld nugget of the joint of the aluminum alloy part is 1 to 20 μm; and no S line is observed at the joint of the aluminum alloy part.

10. The aluminum alloy part according to claim 9, characterized in that: The tensile strength and elongation of the joint of the aluminum alloy part are not less than 97% of the aluminum alloy plate before welding; Preferably, the aluminum alloy part is obtained by the preparation method according to any one of claims 1 to 8.

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