Effect of friction stir welding parameters on microstructure-based defect formation and mechanical properties of Tailor Welded Blanks

Abstract

This maiden work on friction stir welding (FSW) of unequal thickness dissimilar (UETD) materials with plate thickness ratio (PTR) of 2.54 presents a comprehensive analysis of the effect of FSW process parameters on mechanical properties and microstructure-based defect formation of tailor welded blanks (TWBs). In contrast with equal thickness butt joints, the thickness mismatch in TWBs creates various challenges in the process requisite, influencing the process mechanics leading to inadequate heat input and improper mixing of base materials, making the joint prone to various defects. Defects such as tunnel defect, kissing bond defect, voids, and incomplete root penetration (IRP) defect observed and discussed comprehensively in this study are largely attributed to the complexities in the process requisites and mechanics, selection of unfavourable combinations of FSW process parameters, variation of plate thickness, and occurrence of surface oxide layers at the abutting surfaces. The present work included and discussed microstructural features around defects, temperature history, and mechanical properties of joints such as tensile strength and hardness to understand the effect of FSW process parameters on failure mechanism of TWBs in detail. Based on the results obtained from mechanical properties of joints discussed in this study, it was revealed that IRP defect deteriorated the mechanical properties the most followed by tunnel defect, kissing bond defect and voids. Figure: Illustrates (a) FSW set up (b) macrostructure of welded joint (c) tensile specimen and (d) specimen indicating positions of microhardness readings