Quenching-free heat treatment method for improving mechanical property of electric arc additive aluminum alloy

Abstract

The invention relates to a method for improving the mechanical property of an electric arc additive aluminum alloy through quenching-free heat treatment, which comprises the following steps of: designing the components of a quenching-free Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy for electric arc additive: 5.5-7.0 wt% of main alloy element Mg; the content of the trace alloy element Sc is 0.30-0.70 wt%; the trace alloy elements Zn, Ag and Cu are independently added or jointly added, the content of Zn is 0.5-1.5 wt%, the content of Ag is 0.2-1.0 wt%, and the content of Cu is 0.2-1.0 wt%; according to the quenching-free Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy electric arc additive manufacturing technology, a multi-laser-assisted electric arc additive manufacturing method is adopted, efficient melting and high-speed deposition are achieved, the defects of formed air holes and cracks are restrained, and the formed structure is improved; aiming at the aging post-treatment of the electric arc additive quenching-free Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy, a strengthening phase is separated out from a supersaturated solid solution formed by high-speed melting by adopting in-situ aging or low-temperature aging, so that the mechanical property is improved. High-performance manufacturing is achieved under the quenching-free heat treatment condition, and the problem that due to the fact that solid solution quenching heat treatment is needed for conventional high-strength aluminum alloy electric arc material increase, non-uniform deformation is large is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of additive manufacturing and relates to a method for improving the mechanical properties of arc additive aluminum alloy by quench-free heat treatment. Background Art

[0002] At present, high-strength aluminum alloys (such as 2219) formed by electric arc additive manufacturing (WAAM) have been applied in load-bearing components such as payload brackets and cabin sections of aerospace equipment. This type of Al-Cu high-strength aluminum alloy has low mechanical properties in the deposited state due to micro-segregation in the WAAM process, and the tensile strength can only reach about 250MPa. It is necessary to use the method of solid solution, quenching + artificial aging (T6 heat treatment) to increase the tensile strength to more than 400MPa. During the quenching process, high-strength aluminum alloy components formed by WAAM will undergo non-uniform deformation, resulting in insufficient subsequent machining allowance. At present, the method of increasing the blank allowance of WAAM components is generally used to envelope quenching deformation, which results in weight gain of the blank, low material utilization, and a significant increase in manufacturing cost and cycle time.

[0003] The development of quench-free aluminum alloys and corresponding forming processes for WAAM is expected to solve the above problems, but it faces difficulties in both composition design and process design. On the one hand, the WAAM metallurgical process is different from the ultra-fast melting process of the tiny molten pool of selective laser melting additive (SLM). Its molten pool size is several millimeters, and the cooling rate is less than 100℃ / s. The microstructural characteristics such as sedimentary element segregation and grain morphology are between conventional casting and laser additive manufacturing, and show a certain layer-by-layer non-uniformity. There is still a blank for the quench-free aluminum alloy for WAAM designed to match these problems. On the other hand, the conventional WAAM process scanning deposition speed is generally 8-10mm / s, which is 2 orders of magnitude lower than SLM. The degree of solid solution of alloy elements in the matrix is ​​insufficient and the composition supercooling is low, which limits the improvement of solid solution strengthening and fine grain strengthening effects. Summary of the invention

[0004] The technical problem solved by the present invention is: the purpose of the present invention is to solve the problem that conventional arc-added high-strength aluminum alloys need to use solid solution quenching heat treatment to improve the mechanical properties, but the quenching deformation cannot be economically controlled. A method for improving the mechanical properties of arc-added aluminum alloys by quench-free heat treatment is proposed, and high-performance manufacturing is achieved under quench-free heat treatment conditions, avoiding the problem of large non-uniform deformation caused by the need for solid solution quenching heat treatment of conventional high-strength aluminum alloy arc additives.

[0005] The solution to the technical problem of the present invention is to propose a method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment, comprising the following steps:

[0006] (1) Design of Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy composition for arc additive manufacturing:

[0007] Main alloy element Mg, content: 5.5-7.0wt%;

[0008] Trace alloy element Sc, content: 0.30-0.70wt%;

[0009] Trace alloy elements Zn, Ag, and Cu are added separately or in combination, with Zn content of 0.5-1.5wt%, Ag content of 0.2-1.0wt%, and Cu content of 0.2-1.0wt%;

[0010] (2) For the arc additive process of quench-free Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy, a multi-laser assisted arc additive manufacturing method is used to achieve efficient melting and high-speed deposition, inhibit forming pores and crack defects, and improve the forming structure;

[0011] (3) For the post-aging treatment of arc-assisted quench-free Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy, in-situ aging or low-temperature aging is used to precipitate the strengthening phase from the supersaturated solid solution formed by high-speed melting to improve the mechanical properties.

[0012] Furthermore, the trace alloying elements Zn, Ag, and Cu are added alone or in combination, and Zn, Mg, and Al can form an aging precipitation strengthening phase T-Mg 32 (Al, Zn) 49 Ag and Cu can promote the precipitation of T phase to form T-Mg 32 (Al, Zn, Ag) 49 or T-Mg 32 (Al, Zn, Cu) 49 .

[0013] Furthermore, the multi-laser assisted arc additive manufacturing method comprises:

[0014] (1) Integrate multiple laser heads on the consumable arc welding gun used in conventional arc additive processes to form a composite deposition head with central consumable arc + off-axis multi-laser assistance;

[0015] (2) Regulating the multi-laser spatiotemporal energy input to form asymmetric energy input or periodic changes in the circumferential direction, changing the instantaneous temperature gradient of the molten pool, and strengthening the convection circulation inside the molten pool, which not only promotes the escape of pores in the melt, but also refines the grains by stirring and crushing the dendrites during solidification, thus achieving high-quality forming;

[0016] (3) Through multi-laser stable arc plasma and droplet transition, the wire melting efficiency is further improved, and the wire feeding speed of 1.2mm wire reaches 9-15m / min;

[0017] (4) Through multi-laser stable high-speed moving molten pool solidification forming, the cooling rate and composition supercooling during molten pool solidification are improved, the solid solution of alloy elements and grain refinement are promoted, and microsegregation is inhibited.

[0018] Furthermore, the laser heads include 2-6.

[0019] Furthermore, the output power of the laser head is 200-600W, and the multi-laser energy density distribution and input power are adjusted according to the forming structure characteristics and forming process requirements, so that the total power reaches more than 1200W.

[0020] Furthermore, the multi-laser stable high-speed moving molten pool solidification forming process parameters include: multi-laser assisted arc additive scanning speed reaches 40-100mm / s, single layer height is 0.3-1.0mm, and single pass melt width / layer height ratio is 5-15.

[0021] Furthermore, in-situ aging is used to precipitate the strengthening phase from the supersaturated solid solution formed by high-speed melting, including:

[0022] By controlling the waiting time between layers and using blue laser scanning to heat the surface of the deposited layer layer by layer, the temperature and time of multiple-frequency thermal cycles are regulated to allow the strengthening phase to precipitate in situ by aging.

[0023] Furthermore, the waiting time between control layers is 1-10 minutes.

[0024] Furthermore, low temperature aging is used to precipitate the strengthening phase from the supersaturated solid solution formed by high-speed melting, including:

[0025] After the component is formed as a whole, it is subjected to low temperature aging at 120-180℃ for 1-12h to make T-Mg 32 (Al, Zn) 49 、T-Mg 32 (Al, Zn, Ag) 49 or T-Mg 32 (Al, Zn, Cu) 49 Strengthening phase precipitation.

[0026] The beneficial effects of the present invention compared with the prior art are:

[0027] (1) The method of the present invention can ensure that the room temperature tensile strength of arc-added quench-free aluminum alloy is ≥380MPa, the yield strength is ≥260MPa, and the elongation is ≥6%;

[0028] (2) The present invention improves the wire melting efficiency through a multi-laser assisted arc additive manufacturing process, and the aluminum alloy deposition efficiency of a single deposition head reaches 1000cm 3 / h;

[0029] (3) The present invention utilizes a multi-laser assisted arc additive manufacturing process to improve the wall thickness dimensional accuracy of the component, which is better than 0.5 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a flow chart of the method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0032] In view of the problem that conventional arc-added high-strength aluminum alloys need to use solid solution quenching heat treatment to improve mechanical properties, but cannot economically control quenching deformation, the present invention proposes a method for improving the mechanical properties of arc-added aluminum alloys by quenching-free heat treatment from three aspects: arc-added quenching-free aluminum alloy composition design, special forming process, and aging post-treatment. Figure 1 As shown, the specific steps include:

[0033] (I) Design of Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy composition for arc additive without quenching, adopting the multi-scale synergistic strengthening idea of ​​"solution strengthening-in-situ aging-grain refinement", design a new type of WAAM without quenching aluminum alloy with "high Mg solid solution strengthening, Zn / Ag / Cu aging precipitation strengthening, Sc fine grain strengthening". Optimization is carried out by combining thermodynamic calculation of WAAM hot crack sensitivity, aging precipitation kinetic calculation, girth weld hot crack test, and forming process test. The specific composition is as follows:

[0034] (1) Main alloying element Mg, content: 5.5-7.0wt%. High Mg content can make more Mg elements dissolved in the α(Al) matrix, achieving better solid solution strengthening effect.

[0035] (2) Trace alloying element Sc, content: 0.30-0.70wt%. A certain content of Sc forms a primary Al3Sc phase during the solidification of the molten pool, which serves as a nucleation core to promote grain refinement and inhibit the segregation of Mg elements.

[0036] (3) Trace alloying elements Zn, Ag, and Cu are added alone or in combination, with Zn content of 0.5-1.5wt%, Ag content of 0.2-1.0wt%, and Cu content of 0.2-1.0wt%. Zn, Mg, and Al can form an aging precipitation strengthening phase T-Mg 32 (Al, Zn) 49 Ag and Cu can promote the precipitation of T phase to form T-Mg 32 (Al, Zn, Ag) 49 or T-Mg 32 (Al, Zn, Cu) 49 .

[0037] (II) For the arc additive process of quench-free Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy, a multi-laser assisted arc additive manufacturing method is used to achieve efficient melting and high-speed deposition, inhibit forming pores and crack defects and improve the forming structure. The main methods are as follows:

[0038] (1) Multiple (2-6) laser heads are integrated on the consumable arc welding gun used in the conventional WAAM process to form a composite deposition head with central consumable arc + off-axis multi-laser assisted deposition. The laser head output power is 200-600W. The multi-laser energy density distribution and input power can be adjusted according to the forming structure characteristics and forming process requirements. The total power generally reaches more than 1200W.

[0039] (2) Regulating the multi-laser spatiotemporal energy input to form circumferentially asymmetric energy input or periodic changes, changing the instantaneous temperature gradient of the molten pool, and strengthening the convection circulation inside the molten pool, which not only promotes the escape of pores in the melt, but also refines the grains by stirring and crushing the dendrites during solidification, thereby achieving high-quality forming.

[0040] (3) Through multi-laser stable arc plasma and droplet transition, the wire melting efficiency is further improved, and the wire feeding speed of 1.2mm wire reaches 9-15m / min.

[0041] (4) Through the multi-laser stable high-speed moving molten pool solidification forming, the cooling rate and composition supercooling during molten pool solidification are improved, the alloy element solid solution and grain refinement are promoted, and microsegregation is suppressed. The multi-laser assisted arc additive scanning speed reaches 40-100mm / s, the single layer height is 0.3-1.0mm, and the single pass melt width / layer height ratio is 5-15.

[0042] (III) For the post-aging treatment of arc-assisted quench-free Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy, in-situ aging or low-temperature aging is used to precipitate the strengthening phase from the supersaturated solid solution formed by high-speed melting to improve the mechanical properties. The method is as follows:

[0043] (1) In-situ aging is used to precipitate the strengthening phase from the supersaturated solid solution formed by high-speed melting, including: by controlling the interlayer waiting time (1-10 minutes), the surface of the deposited layer is heated by blue laser scanning layer by layer to control the temperature and time of multiple frequency thermal cycles, so that the strengthening phase is precipitated by in-situ aging.

[0044] (2) Low temperature aging is used to precipitate the strengthening phase from the supersaturated solid solution formed by high-speed melting, including: after the component is formed as a whole, low temperature aging is performed at 120-180°C for 1-12h to make the T-Mg 32 (Al, Zn) 49 、T-Mg 32(Al, Zn, Ag) 49 or T-Mg 32 (Al, Zn, Cu) 49 Strengthening phase precipitation.

[0045] Example 1

[0046] This example uses a new Al-Mg-Sc-Zn wire and a multi-laser assisted arc additive manufacturing process to form a 250mm×180mm single-wall structure. After aging at 180℃ for 6h, the transverse and longitudinal tensile mechanical properties are tested. The specific implementation process and results are as follows:

[0047] (1) Design the wire composition and customize the wire according to the idea of ​​"high Mg solid solution strengthening, Zn / Ag / Cu aging precipitation strengthening, Sc fine grain strengthening". The wire composition re-test results are: Mg, 5.8wt%; Zn, 0.7wt%; Sc, 0.6wt%; Mn, 0.4wt%; Ti, 0.15wt%; Si, 0.02wt%; Fe, 0.02wt%; Al, the rest.

[0048] (2) A 4-laser assisted CMT arc additive manufacturing process was used to form a single-wall structure. Each blue laser had an output power of 300 W, a wire feeding speed of 9 m / min, a scanning speed of 80 mm / s, an interlayer dwell time of 20 s, a layer height of 0.5 mm, and a melt width of 4.1 mm.

[0049] (3) The formed single-wall wall is subjected to low-temperature aging as a whole, and kept at 175°C for 6 hours.

[0050] (4) The tensile mechanical properties were tested in both the horizontal and vertical directions. The horizontal direction showed: tensile strength 422MPa-426MPa; yield strength 298-304MPa; elongation after fracture 10.5-12.0%. The vertical direction showed: tensile strength 376MPa-411MPa; yield strength 287-291MPa; elongation after fracture 7.0-8.5%.

[0051] The present invention is applied to large-scale arc-added aluminum alloy components of aerospace equipment, achieving high-performance manufacturing under quench-free heat treatment conditions, avoiding the problem of large non-uniform deformation caused by conventional high-strength aluminum alloy arc-added components requiring solid solution quenching heat treatment.

[0052] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

[0053] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment, characterized in that: The following steps are involved: (1) Design of Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy composition for arc additive manufacturing: Main alloy element Mg, content: 5.5-7.0wt%; Trace alloy element Sc, content: 0.30-0.70wt%; Trace alloy elements Zn, Ag, and Cu are added separately or in combination, with Zn content of 0.5-1.5wt%, Ag content of 0.2-1.0wt%, and Cu content of 0.2-1.0wt%; (2) For the arc additive process of quench-free Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy, a multi-laser assisted arc additive manufacturing method is used to achieve efficient melting and high-speed deposition, inhibit forming pores and crack defects, and improve the forming structure; (3) For the post-aging treatment of arc-assisted quench-free Al-Mg-Sc-(Zn / Ag / Cu) aluminum alloy, in-situ aging or low-temperature aging is used to precipitate the strengthening phase from the supersaturated solid solution formed by high-speed melting to improve the mechanical properties.

2. The method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment according to claim 1 is characterized in that: The trace alloying elements Zn, Ag and Cu are added alone or in combination, and Zn, Mg and Al can form an aging precipitation strengthening phase T-Mg 32 (Al, Zn) 49 Ag and Cu can promote the precipitation of T phase to form T-Mg 32 (Al, Zn, Ag) 49 or T-Mg 32 (Al, Zn, Cu) 49 .

3. The method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment according to claim 1, characterized in that: The multi-laser assisted arc additive manufacturing method comprises: (1) Integrate multiple laser heads on the consumable arc welding gun used in conventional arc additive processes to form a composite deposition head with central consumable arc + off-axis multi-laser assistance; (2) Regulating the multi-laser spatiotemporal energy input to form asymmetric energy input or periodic changes in the circumferential direction, changing the instantaneous temperature gradient of the molten pool, and strengthening the convection circulation inside the molten pool, which not only promotes the escape of pores in the melt, but also refines the grains by stirring and crushing the dendrites during solidification, thus achieving high-quality forming; (3) Through multi-laser stable arc plasma and droplet transition, the wire melting efficiency is further improved, and the wire feeding speed of 1.2mm wire reaches 9-15m / min; (4) Through multi-laser stable high-speed moving molten pool solidification forming, the cooling rate and composition supercooling during molten pool solidification are improved, the solid solution of alloy elements and grain refinement are promoted, and microsegregation is inhibited.

4. The method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment according to claim 3 is characterized in that: The laser heads include 2 to 6 laser heads.

5. The method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment according to claim 3 is characterized in that: The output power of the laser head is 200-600W. The multi-laser energy density distribution and input power are adjusted according to the forming structure characteristics and forming process requirements so that the total power reaches more than 1200W.

6. The method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment according to claim 3 is characterized in that: The multi-laser stable high-speed moving molten pool solidification forming process parameters include: the multi-laser assisted arc additive scanning speed reaches 40-100 mm / s, the single layer height is 0.3-1.0 mm, and the single pass melt width / layer height ratio is 5-15.

7. The method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment according to claim 1, characterized in that: In-situ aging is used to precipitate the strengthening phase from the supersaturated solid solution formed by high-speed melting, including: By controlling the waiting time between layers and using blue laser scanning to heat the surface of the deposited layer layer by layer, the temperature and time of multiple-frequency thermal cycles are regulated to allow the strengthening phase to precipitate in situ by aging.

8. The method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment according to claim 7, characterized in that: The waiting time between control layers is 1-10 minutes.

9. The method for improving the mechanical properties of arc-added aluminum alloy by quench-free heat treatment according to claim 2, characterized in that: Low temperature aging is used to precipitate the strengthening phase from the supersaturated solid solution formed by high-speed melting, including: After the component is formed as a whole, it is subjected to low temperature aging at 120-180℃ for 1-12h to make T-Mg 32 (Al, Zn) 49 、T-Mg 32 (Al, Zn, Ag) 49 or T-Mg 32 (Al, Zn, Cu) 49 Strengthening phase precipitation.

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