Friction stir welding ( FSW) lap joints of 3 mm-thick LY12 aluminum alloy sheets were made using a cylindrical tool with right-hand threaded pin, and the effects of plunge depth of shoulder on the interface migration and mechanical properties of resultant joints were investigated. The results show that the lap interfaces on both sides of weld nugget moved downward , and the height of interface migration rose with increase of plunge depth of shoulder. The height of interface migration was greater on the retreating side than on the advancing side. The interfaces on both sides of weld moved slightly when using an appropriate plunge depth of shoulder. The shear strength of laprnjoint was excellent due to the slight interface migration, and fracture occurred in the top sheet. However, when the interfaces at both sides of weld moved downward, fracture occurred in the bottom sheet. The shear strength decreased with increase of the height of interface migration. The shear strength was higher when the load was exerted on the advancing side than on the retreating side.%采用表面为右螺纹圆柱型搅拌针的搅拌头对3mm厚LY12铝合金进行了搅拌摩擦焊搭接试验,研究了轴肩下压量对接头界面迁移和搭接接头力学性能的影响.结果表明,随轴肩下压量增大,焊缝两侧的搭接界面均向下迁移,其迁移量随下压量的增加而增加,焊缝返回侧的界面迁移量大于前进侧.控制轴肩下压量,当轴肩下压量合适时,焊缝两侧的界面仅发生较小的迁移.当焊缝两侧的界面仅发生较小的迁移量时,搭接接头有较高的抗剪强度,且断裂都发生在上板,呈正断.焊缝两侧的搭接界面向下迁移时,断裂都发生在下板,接头抗剪强度随界面迁移高度的增加而减小,且受拉侧在下板前进侧时,接头的抗剪强度较受拉侧在下板返回侧时的高.
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