Study of Weld Characteristics in Friction Stir Welding of Dissimilar Mg-Al-Zn Magnesium Alloys under Varying Welding Conditions

Magnesium alloys are lightweight structural material with attractive specific strength and require joining of different pieces in many industrial applications. Due to their low melting temperature, chemically active elements and high thermal expansion these alloys are difficult-to-weld by conventional welding techniques. Friction Stir Welding has favorable characteristics to weld these alloys but dissimilarity in workpieces pose problem to achieve required weld characteristics. The present research experimentally investigates the weld characteristics in Friction Stir Welding of dissimilar AZ31 and AZ91 Mg alloys under varying processing parameters. The research outcomes show that shoulder diameter and rotational speed of tool were the most influencing parameters followed by welding speed in most of the cases. Grain size increases with increase in rotational speed and shoulder diameter. There was no presence of intermetallic compound in stir zone but some cracks were observed. Maximum tensile strength in weld zone was 89.71% and all the tensile samples break from 1 to 3 mm away from weld center line. Maximum average microhardness and flexural strength were 72.51 +/- 6.82 HV and 380.06 +/- 13.43 MPa, respectively, while flexural load vs elongation curve was almost similar to base material.