Analysis of SiC nano-powder effects on friction stir welding of dissimilar Al-Mg alloy to A316L stainless steel

In this work, dissimilar friction stir welding (FSW) of an Al-Mg alloy (AA5083) to austenitic stainless steel (A316L) by using nano sized SiC reinforcement was examined. Two optimized traverse velocities of 16 and 20 mm/min (and a constant rotational speed of 250 rpm) with the intact joint appearance were considered for investigation the effect of number of passes on microstructural and mechanical properties. Microstructure of the single-pass FSWed specimens containing reinforcements indicated large steel fragments and agglomerated SiC particles within the stir zone (SZ). Further FSW passes led to more homogenous distribution of SiC particles and steel fragments. Field emission-scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) were employed to analyze the in situ reactions at the joint interface and stir zone of Al-Mg alloy. No marks demonstrating the formation of tunneling defects were revealed at the stir zone up to six passes. Furthermore, streaks of tiny intermetallic particles together with steel fragments aligned in the direction of material flow. Tensile tests indicated that after six passes of FSW at traverse velocity of 16 mm/min, the joint strength ratio to the ultimate tensile strength (UTS) of the AA5083 base metal (BM) was boosted up to ∼94 %, with an elongation reduction to 3% and a Vickers hardness enhancement of 250% in the stir zone.