中文摘要：

与薄 Zn 夹层的增加， 2.4  mm 厚 Mg3Al1Zn 合金表是磨擦与公寓用一个无大头针的工具搅动焊接的点(FSSW ) ，凸并且凹面肩膀形状。结果证明 alloying 反应在 FSSW 期间发生在 Mg 底层和 Zn 夹层之间，形成创作的不连续的 intermetallics 层散(-Mg + MgZn) 在肩膀和 MgZn 下面的最容易溶解的结构在关节的外面的 intermetallics 结合地区。这 alloying 反应增加了结合的区域并且消除了钩缺点，没有钩，从而与一个浅锁眼生产健全 FSSW 关节背叛。增加跳入深度对 MgZn 散开有益，从而增加关节的张力砍负担。然而，过多跳入深度导致了有效的表厚度的减少，减少关节的力量。在一小跳入深度，凸并且凹面肩膀比扁平的肩膀对接口反应更有益。6.6  kN 的最大的联合负担被在 1.0  mm 的 plunge 深度使用凹面肩膀完成。一个 welding 以后热处理在关节支持了不连续的反应层的溶解；然而，它导致了空缺点的出现，影响结合的力量。

英文摘要：

With the addition of a thin Zn interlayer, 2.4 mm thick Mg-3AI-1Zn alloy sheets were friction stir spot welded （FSSW） using a pinless tool with fiat, convex and concave shoulder shapes. The results showed that an alloying reaction took place between the Mg substrate and Zn interlayer during FSSW, forming a discontinuous intermetallics layer composed of dispersive （α-Mg ＋ MgZn） eutectic structure under- neath the shoulder and a Mg-Zn intermetallics bonding zone at the outside of the joints. This alloying reaction increased the bonded area and eliminated the hook defects, thereby producing sound FSSWjoints with a shallow keyhole without hook defects. The increase of plunge depth was beneficial to the Mg-Zn diffusion, thereby increasing the tensile-shear load of the joints. However, excessive plunge depths re- sulted in a decrease of the effective sheet thickness, reducing the strength of the joints. At a small plunge depth, the convex and concave shoulders were more beneficial to the interface reaction than the fiat shoul- der. The maximum joint load of 6.6 kN was achieved by using the concave shoulder at a plunge depth of 1.0 mm. A post-welding heat treatment promoted the dissolution of the discontinuous reaction layer in the joints; however, it led to the occurrence of void defects, influencing the bonding strength.