中文摘要：

研究了搅拌摩擦焊焊接铜合金、铝合金时接头中出现的洋葱环结构，分析其形成及影响因素。结果表明：洋葱环的实质是搅拌针旋转前进时其带动的软化层与上一软化层塑性金属间相对移动摩擦叠加后产生的一种轨迹；由于搅拌针区域摩擦热输入不足，层间新生成的晶核呈弥散分布，层间与层内晶粒形状不同，从宏观上看，接头纵剖面上形成了结构重叠的半圆环结构，而从横剖面上就形成了独特的“洋葱环”结构；焊缝中心纵剖面上出现环间距大小与搅拌针旋转一周向前移动的距离基本相等。

英文摘要：

The onion rings structures in the joints of Cu alloy and Al alloy welded by friction stir welding were studied, and their formation and influence factors were analyzed. The results show that the key of forming onion rings structure is a trace in a way the plastic metal softened shell layers around the friction stir pin were shifted, superimposed and fractionated between the former plastic layer. The grains between the layers ware dispersed, and which are different from the grains in the layers due to low friction heating in the friction stir pin zone. From macroscopic point of view, the overlapped semicircle structures form in the longitudinal section of the joint while the special onion rings structure emerge in the cross-section. The study also discovered that the distance between the layers in the longitudinal section of the center joint nearly equals to the forward step over which the stir pin rotating a circuit are forced to move forward.