中文摘要：

采用搅拌摩擦焊对5mm厚7050铝合金板进行焊接,对焊核区洋葱环的宏观形貌、微观组织进行分析,并研究洋葱环对接头性能的影响.结果表明：焊核区出现的洋葱环组织实际是由粗晶带与细晶带相间构成的;当v=80mm/min、ω=600r/min时,焊核区形成完整的椭圆形洋葱环,随着转速提高,洋葱环的形状逐渐不规则;而当转速恒定时,随着焊速的提高,洋葱环逐渐变小;在接头中心预制缺口,然后进行拉伸试验,发现裂纹都是沿预制缺口经洋葱环中粗晶晶界扩展,表明环上粗晶带的出现会加速焊核区的裂纹扩展.

英文摘要：

7050 aluminum alloy plates with thickness of 5 mm were welded with friction stir welding, the macromorphology and microstructure of onion ring in welding nucleus zone were analyzed, and the effect of onion rings on the welded joint performance was investigated. The result showed that the onion ring structure in welding nucleus zone was actually composed of coarse grain belt interlaced with fine grain belt. When the welding speed was 80 mm/min and rotational speed was 800 r/min, an integral elliptic onion ring would appear in the welding nucleus zone. With the increase of rotational speed, the shape of the on- ion ring would gradually become irregular. When the rotational speed was constant, with the increase of welding speed, the onion ring would gradually become small. By preparing a notch at the weld joint cen- ter, a tensile test was performed. It was found that all cracks would propagate along the notch and through the coarse grain boundary in the onion ring, manifesting that the emergence of coarse grain belt in onion ring would accelerate the propagation of crack in the welding nucleus zone.