Tensile strength and microstructure of laser welding of AZ31 magnesium alloy thick plates

To deepen the understanding of laser welding of magnesium alloys,a high power CO2 laser was employed to join AZ31 magnesium alloy in 10mm thick.Its microstructure and tensile strength of laser welds were studied.Obvious concaves appeared on the welding surface because of serous burning-lost of magnesium at high temperature.Under the experimental conditions,the microstructure of the welding zone was equiaxed dendrites and the grains were refined with the decrease of the welding heat.The tensile test results showed surface concaves and porosities were two main factors affecting the tensile strength. The maximum tensile strength was only 74% of the substrate metal if the surface including concaves.However,it reached 91% of the substrate metal after surface concaves were eliminated by laser repair welding.Besides,the porosities were the main affecting factor inducing the tensile strength of laser repair weld is lower than that of the substrate metal.The results show it is necessary to eliminate the surface concaves and weld porosities in order to increase the mechanical property of laser welding joints.