Laser welding-brazing of Mg to stainless steel: joining characteristics, interfacial microstructure, and mechanical properties

Abstract

Magnesium alloy and stainless steel were joined by dual-beam laser welding-brazing process. The effect of the main process parameters including welding speed, wire feed speed, and heat input on weld appearance of the dissimilar joint was investigated. The microstructures of both welded and brazed side were observed using scanning electron microscopy (SEM) and identified by transmission electron microscopy (TEM). Mechanical properties were then studied. Formation of continuous thin reaction layer was observed along the fusion zone-steel interface, which was thereafter identified as FeAl intermetallic compound. The thickness was in the range of 0.9–2.9 μm, varied slowly with the increase of heat input. The tensile-shear test indicated that high joint strength was achieved at a wide range of heat input, with a maximum value of 274.5 N/mm, reaching 83.8 % of that of Mg base metal. The corresponding failure occurred in the heat-affected zone (HAZ) of the Mg base metal. While joints fractured at the interface or fusion zone at low/high heat input due to weak bonding or porosity formation at fusion zone.