X. Cao, M. Jahazi, NRC Institute for Aerospace, Montreal, QC, Canada
Friction stir welding (FSW) is a relatively new joining process. To date research and development has been mainly concentrated on aluminium alloys. Limited results have been reported on magnesium alloys, in particular, little is known about the lap welding of magnesium alloys. As an inexhaustible metal, magnesium alloys have rather attractive properties due to their low density, excellent specific strength, excellent sound damping capabilities, good castability, excellent machinability, good electromagnetic interference shielding and recyclability. As one of the lightest materials for structural applications, magnesium alloys are increasingly used in aerospace, aircraft, automotive, electronic and other industries. To further expand the application of magnesium alloys more effective welding and joining techniques are required. In this work, the effect of welding speed ranging from 5 to 30 mm/s on the weld quality of 2-mm AZ31 magnesium alloy lap joints was systematically investigated. The influence of welding speed on welding defects such as hooking, kissing bond, and top plate thinning is discussed in detail. Also, the evolution of the microstructure, microindentation hardness and tensile shear load as a function of process parameters were determined and are discussed in the present work. The welding process of the lap joints for 2-mm AZ31 magnesium alloy was optimized based on the minimization of the welding defects and the maximum tensile shear strength. Sound lap joints with good surface quality, low distortion, lack of pores and cracks, with minor hooking and kissing bond defects, and with high tensile shear strength were successfully obtained indicating the great potential of FSW technique for joining magnesium alloys.
Summary: Effect of welding speed on lap joint quality of AZ31 magnesium alloy was systematically investigated from defects, microstructure, hardness and tensile shear load. Sound joints with good surface quality, without or with minor defects and high shear load were successfully obtained indicating great potential of FSW technique for magnesium alloys.
