7075Al合金传统的电弧焊接头具有较高的开裂倾向，接头强度和耐腐蚀性能较母材大幅下降，因此被认为难以采用传统的电弧焊接工艺进行焊接。本工作采用先进的交流冷金属过渡(AC-CMT)电弧焊工艺降低热输入，利用ER7075焊丝保证焊缝与母材等成分匹配，解决7075铝合金传统电弧焊接性差的问题，并系统研究焊后T6热处理对焊缝组织和力学性能的优化作用，旨在获得与母材性能相匹配的高质量焊接接头。利用自制ER7075焊丝对7075Al合金进行了AC-CMT电弧焊，研究了热处理前后焊接接头的组织及力学性能。结果表明，7075Al合金AC-CMT电弧焊焊缝成形美观，除了熄弧部位偶尔会出现弧坑裂纹外，焊缝其他部位未发现裂纹。焊态下，焊缝金属的晶界上存在大量的条状和点状T相(Mg(Zn, Cu, Al)₂ + Al共晶相)及h相(Mg(Zn, Cu, Al)₂相)，晶内未发现弥散的沉淀析出相，接头的平均抗拉强度为349 MPa，延伸率为4.48%。T6热处理后，焊缝金属的晶粒尺寸明显增大，而影响区的晶粒尺寸基本不变；晶界析出相基本消失，晶内和晶界上均析出了大量弥散分布的GP区和强化相h¢(MgZn₂)，接头抗拉强度提高到538 MPa，接近母材的抗拉强度(540 MPa)，延伸率提高到6.11%，达到母材的55.5%。

The 7075 Al alloy has garnered widespread attention in various industrial fields including aerospace, aviation, high-speed rail, and automobile manufacturing owing to its high strength, excellent ductility, and corrosion resistance. However, welding this alloy using conventional arc welding processes is challenging because the high heat input and the application of dissimilar filler materials result in high cracking susceptibility and remarkable reductions in the strength and corrosion resistance of the welded joint compared with the parent material. Recently, alternating current cold metal transfer (AC-CMT) arc welding has been extensively used as a promising solution. Herein, AC-CMT arc welding, which is an inherently low heat-input welding process, was used to weld 7075 Al alloy using a self-made ER7075 welding wire. The microstructure and mechanical properties of the welded joints before and after heat treatment were studied using optical microscopy, SEM, TEM, and a universal tensile testing machine. The results revealed that the AC-CMT arc-welded 7075Al alloy exhibited a smooth weld appearance; no cracks were observed, except for occasional arc-crater cracks in the extinguishing area. In the as-welded metal, a large number of strip-shaped and dot-like T phases (Mg(Zn, Cu, Al)₂ + Al eutectic phase) and h phase (Mg(Zn, Cu, Al)₂ phase) were present along the grain boundaries, whereas no dispersed precipitates were observed within the grains. The average tensile strength of the as-welded joint was 349 MPa, and the elongation was <4.48%. After postweld T6 heat treatment, the grain size of the weld metal remarkably increased, whereas the grain size of the heat-affected zone remained almost unchanged. The precipitates at the grain boundary almost disappeared, and a majority of dispersed GP regions and strengthening h¢(MgZn₂) phases precipitated inside the grains and along the grain boundaries.The dispersed GP regions and strengthening h¢ phases can effectively hinder grain boundary migration and significantly improve material strength. The continuous precipitated phases on the original grain boundaries disappear due to solid solution, reducing the fragile area of the grain boundaries and making the overall mechanical properties of the joint close to the level of the base material. The tensile strength of the T6-treated welded joint was increased to 538 MPa, which is almost equal to the tensile strength of the base material (540 MPa), whereas the elongation increased to 6.11%, reaching 55.50% of the base material. The postweld T6 heat treatment also shifted the fracture location from the center of the weld to near the fusion line.