Pinless Friction Stir Spot Welding of Mg?3Al?1Zn Alloy with Zn Interlayer

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