中文摘要：

用搅拌针长度为3.6 mm的圆柱左螺纹和右螺纹搅拌头对3 mm厚的LY12（CZ）铝合金进行了搅拌摩擦焊搭接试验,研究了双道焊搭接界面的迁移及接头的性能.结果表明,搅拌头顺时针旋转,采用左螺纹搅拌头时,焊核两侧的搭接界面向上迁移;采用右螺纹搅拌头时,搭接界面向下迁移.单道焊时,由于受拉边总存在迁移界面,导致有效承载板厚减小.用左、右螺纹搅拌头交替进行双道焊接,形成焊缝一侧的搭接界面向上迁移,另一侧的搭接界面向下迁移,使接头承载时,消除迁移界面对受拉边的影响,接头的强度可达到单道焊接头的两倍以上.

英文摘要：

Friction stir lap joints of 3 mm thick plates of LY12（CZ） aluminum alloy were conducted using the cylindrical tool with clockwise and counter-clockwise screw thread.The interface migration and mechanical property of friction stir lap joint of double passes weld were investigated.The results show that,the interfaces at both sides of the welds pull-up using the tool with counter-clockwise screw thread when the tool rotating clockwisely,while the interfaces pull-down using the tool with clockwise screw thread.With single pass weld,the effective sheet thickness（EST） is reduced because the interface migratory always exists on the loaded side.The interface appearance at one side of the weld pull-up and the other side pull-down was obtained if the tool with clockwise and counter-clockwise screw thread were used alternately by double passes weld.The strength of double passes welds could reach more than twice as the single pass weld because of avoiding the influence of the interface migration on the loaded side.