Influence of SiC Powders on Aluminium Alloy 7075-T6 Joints by Friction Stir Welding Process

Abstract

Friction Stir Welding (FSW) is a process of joining two similar or dissimilar materials by the application of heat generated between two contact surfaces. The main advantage of FSW is that during the welding process, the materials are joined with lesser heat and increased bond strength. However, there is a lot of scope for increasing the mechanical and metallurgical properties of the weldments. Silicon Carbide (SiC) in powder form has an impact in the enhancement of mechanical and metallurgical properties. Hence, in the present work the influence of SiC powders on mechanical and metallurgical properties of AA 7075-T6 joints fabricated by single pass FSW was analysed. Totally 18 samples of friction stir welded aluminium alloy were taken, of which nine samples without SiC powders and the remaining with SiC powders. The samples were subjected to various tool speeds and traverse speeds keeping the axial force/load constant. The tool used for making the samples is high carbon steel D3 (heat treated to 58-60 HRC). During FSW process parent material gets mixed with the SiC powders due to severe stirring process in the nugget zone and powders will get distributed along the weld length. Microstructural study was conducted across various zones of welded samples (nugget zone, thermo mechanically affected zone, heat affected zone and unaffected base material) to understand the grain boundary behaviour. Scanning electron microscopic analysis (SEM) analysis was carried out in the nugget zone to determine the material flow due to stirring process and also to observe the deposition of SiC powders. Tensile strength for all the fabricated joints were evaluated and correlated with the microstructures, microhardness values of the weldments. Finally, the results of mechanical and metallurgical properties were compared with the weldments made without SiC powder and with SiC powder. It was observed that weldments made with SiC powders showed superior improvement of material behaviour in both mechanical and metallurgical properties.