采用熔化极惰性气体保护焊（MIG焊）工艺对A7N01铝合金T形接头两侧分别进行单、双道焊接，研究了接头的显微组织、显微硬度和疲劳性能，分析了单、双道焊接的影响。结果表明：单道焊侧从熔合区至焊缝中心的显微组织依次由细晶、柱状晶和等轴晶组成，双道焊侧熔合线附近的显微组织与单道焊侧的相似，在两道焊缝交界处形成了柱状晶，且第一道焊缝的柱状晶相对粗大；接头两侧的母材区均存在软化区，且单道焊侧的软化程度更明显；两侧分别为单、双道焊接接头的疲劳寿命比两侧均单道焊的短，疲劳裂纹萌生于焊趾表面并向内部扩展，断口呈现准解理断裂和韧性断裂的混合断裂模式。

Single-pass and double-pass welding were carried out on both sides of A7N01 aluminum alloy T-joint by metal inert-gas welding (MIG welding), respectively. The microstructure, microhardness and fatigue property of the joint were studied, and the influence of sing-pass and double-pass welding was analyzed. The results show that on the single-pass welding side, the microstructure was composed in order of fine grains, columnar grains and equiaxial grains, from fusion zone to weld center. The microstructure near fusion line on the double-pass welding side was similar to that on the single-pass welding side; near the interface between the two welds, columnar crystals were formed, and the columar crystals in the weld of the first pass was relatively coarse. Softening zone existed in base metal on both sides of the joint, and the softening degree on the single-pass welding side was more obvious. The joint by single-and double-pass welding on both sides, respectively, had a shorter fatigue life than the joint by single-pass welding on both side had; the fatigue crack originated on surface of the weld toe and propagated inside; the fracture presented a mixed fracture mode of quasi-cleavage fracture and ductile fracture.