On the mechanical, microstructural, and corrosion properties of pulsed gas tungsten arc and friction stir welded RZ5 rare earth grade magnesium alloy

Abstract

Experimental studies have been conducted on the microstructure, mechanical, and corrosion characteristics of magnesium alloy RZ5 that has been butt welded. Pulsed tungsten inert gas (PTIG) and friction stir welding (FSW) are two distinct welding techniques that have been considered. The weld metal of the PTIG joint exhibited finer grain cast structures of 10 μm with coarser intergranular eutectic τ-Phase particles as compared to the coarse-grained cast base metal microstructure of 104 μm. The FSW joints microstructural investigation revealed that the precipitates with globular morphology had spread out throughout the wrought ultrafine α-Mg grains of 2 μm. X-ray elemental distribution and phase analysis indicated that in base metal and weld joints, the grain boundaries and interior zones were enriched with Zn and Zr elements with corresponding secondary phases. Microhardness measurements showed the softening is reduced in the heat-affected zone of FSW compared to PTIG joints. The stir zone exhibits the highest hardness of 120.4 HV0.2 which is 40% higher than the fusion zone hardness of PTIG welds. Electrochemical polarization scans and immersion testing indicated that the weld zone of the FSW joint exhibits higher corrosion resistance than the RZ5 base alloy and PTIG welds. The corrosion data (i.e., higher corrosion potential, lower current density, and higher breakdown potential) obtained from the polarisation scans are correlated with the microstructural features after immersion testing.