Effect of Alloying Elements in Steels on the Interfacial Structure and Mechanical Properties of Mg to Steel by Laser-GTAW Hybrid Direct Lap Welding

Abstract

Mg alloy AZ31B was directly bonded to SK7 with a low alloy content, DP980 with a high Mn content, 316L with a high Cr and high Ni content by laser-gas tungsten arc welding (GTAW) and hybrid direct lap welding. The results showed that the tensile loads of AZ31B/SK7 and AZ31B/DP980 joints were 283 N/mm and 285 N/mm respectively, while the tensile load of AZ31B/316L joint was only 115 N/mm. The fracture and interface microstructures were observed using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and identified through X-ray diffractometry (XRD). For AZ31B/SK7 and AZ31B/DP980, the interface of the front reaction area and the keyhole reaction area was mainly composed of an Fe-Al phase and an Al-Mn phase. However, for AZ31B/316L, the interface of the keyhole reaction area was mainly composed of an Fe-Al phase and an Al-Mn phase, but a multi-layer composite structure consisting of the Mg17Al12 compound layer and eutectic layer was formed in the front reaction area, which led to a deterioration in the joint property. The influencing mechanism of Mn, Cr and Ni elements in steel on the properties and interface structure of the laser-GTAW lap joint between the Mg alloy and the steel was systematically analyzed.