Effect of Post-Weld Heat Treatment on the Microstructure and Mechanical Properties of Friction Stir Welds of Cu–Cr–Zr–Ti Alloy

Abstract

In the present study, the effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of the friction stir welded Cu–Cr–Zr–Ti alloy was studied with the aid of optical and transmission electron microscopy, tensile testing, and microhardness measurement. In the as-welded condition, the stir zone was characterized with fine recrystallized grains and thermo-mechanically affected zone showed a necklace structure. The microstructure of heat-affected zone and base metal showed equiaxed grains with annealing twins. Welded samples were subjected to three different PWHT: (a) direct aging, (b) solution treatment, and (c) solution treatment and aging. PWHT showed the effect on the microstructure of the weld with changes in the grain size and formation of precipitates. The microhardness across the weld was highest for the direct aged samples, whereas solution treated samples showed minimum hardness. The yield strength and elongation in as-welded condition were 158 MPa and 18%, respectively. Direct aging of the welded samples resulted in an improvement in the yield strength (171 MPa) with a decrease in ductility (13%). Significant softening of weld was observed after solution treatment, and yield strength was lower than that of base metal. Solution treatment and aging yielded an increase in elongation with a minor decrease in the yield strength. The increase in yield strength of the weld after aging is attributed to the formation of fine chromium precipitates.