Lap-shear performance of weld-bonded Mg alloy and austenitic stainless steel in three-sheet stack-up

Abstract

To overcome the challenges encountered in conventional resistance spot welding (RSW) of three-sheet stack-up involving Mg alloy and austentic stainless steel (ASS), the feasibility of using weld-bonding was investigated. The microstructure and mechanical properties of the joints (Mg alloy/ASS/ASS) were investigated. The Mg alloy and upper ASS were joined together by the combined effect of the cured adhesive and welding-brazing in the weld zone, while a metallurgical bond was formed at the ASS/ASS interface. The Mg nugget microstructure exhibited fine columar grains consisting of largely primary α-Mg grains and eutectic mixture of α-Mg and β-Mg17Al12. The nugget formed at the ASS/ASS interface consisted largely of columnar grains of austenite, with some equiaxed dendritic grains formed at the centerline of the joint. The weld-bonded joints exhibited an average peak load and energy absorption of about 8.5 kN and 17 J, respectively (the conventional RSW joints failed with little or no load application). As the welding current changed, two types of failure modes were observed: Interfacial failure via the Mg nugget/upper ASS interface and partial interfacial failure (part of the Mg nugget was pulled out of the Mg sheet). Both failure modes were accompanied by cohesive failure in the adhesive zone.