Microstructure and mechanical properties of laser welding of AZ31B magnesium alloy and DP590 dual-phase steel with concave groove joint

Abstract A novel connection method has been explored for laser welding of AZ31B magnesium alloy and DP590 dual-phase steel, where lap joint with concave groove was added by Sn powder. The influence of groove width on the interface reaction and mechanical properties of the joint was also studied. The result show that the boundary surface of the concave groove was mainly divided into two regions. One was the laser directly irradiated area which was mainly composed of FeAl + Mg2Sn + α-Mg. As the width of the concave groove increased, the phase composition of the interface changed from FeAl + Mg2Sn + α-Mg to FeAl + FeSn + Mg2Sn + α-Mg. The other was the side boundary area of the concave groove, where a large amount of Sn was transferred from the directly irradiated area, thus the columnar Mg2Sn + α-Mg crystal grains were larger than the directly irradiated area. This interface was mainly composed of FeAl + Mg2Sn + α-Mg. The calculation results of the atomic chemical potential were shown that the Al atoms from the base material diffused to the Fe side in the Mg-Al-Sn-Fe system, which made it easier to form the FeAl phase at the interface. At the Fe interface, Fe and Sn atoms were attracted by Al atoms, which promoted the reaction between Fe atoms and Sn atoms. The maximum load value reaches 1711 N with 1.5 mm width of concave groove, representing twice enhancement compared with that with no-concave groove.