Microstructural, Mechanical and Tribological Characterization of Friction Stir Welded A7075/ZrB2 In Situ Composites

Abstract

Friction stir welding (FSW) has emerged as an efficient technique for the welding of aluminum alloys. However, its potential for the welding of particulate reinforced aluminum matrix composites (AMCs) is yet to be explored fully. The reinforcements affect welding process because it complicates microstructural modifications in weld zone, mainly in nugget zone (NZ). Thus, the present study was aimed to investigate the effect of FSW process on microstructural features and assess the quality of weld after welding of A7075/ZrB2 in situ composites. The microstructural features were captured through optical microscopy, scanning electron microscopy and electron back-scattered diffraction technique. The results revealed, after friction stir welding, that ZrB2 clusters broke completely and dispersed uniformly in the NZ. It was also observed that aluminum matrix experienced substantial grain size reduction due to dynamic recrystallization caused by frictional heat and plastic deformation. The joint efficiency of the welded structure was judged by tensile test. The obtained result revealed a higher value (≥ 90%) which may be ascribed to grain size reduction, uniform dispersion of ZrB2 particles and increased particle/matrix interface characteristics along with eradication of casting defects. The improved microstructural features led to higher hardness and wear resistance in NZ of friction stir welded composite. Spalling and delamination were predominant wear mechanisms in the welded and un-welded as-cast A7075 alloys, whereas these mechanisms were not significant in welded as well as un-welded A7075/ZrB2 in situ composites.