Enhancing the Surface Quality and Tribomechanical Properties of AA 6061-T6 Friction Stir Welded Joints Reinforced with Varying SiC Contents

Abstract

Obtaining high-quality AA6061-T6 weldment is difficult because of the dissolution of its strengthening precipitates at temperatures beyond 250°C. In this work, the surface quality, mechanical and wear properties of AA6061-T6 friction stir welded joints at varying SiC addition (0.56-1.72 g) and number of weld passes (1-6) were investigated and discussed. SiC content was varied by changing the center groove width (CGW). Also, microstructure analysis of the entire welded joints was performed. For the first time, a process map predicting the surface characteristics of SiC reinforced AA6061-T6 friction stir welded joint at varying combinations of CGW and number of weld passes was developed. Increasing the number of passes resulted in better matrix refinement, particles fragmentation and improved particles distribution while increase in SiC content produced particles clustering and lower particles fragmentation. All the reinforced joints showed higher hardness but lower ductility than the unreinforced joint. Only joints reinforced with 0.56 g SiC showed improved tensile strength than the unreinforced joint (156 MPa) with the highest value of ~196 MPa (67% of the base metal) obtained at 4 weld passes. Increased hardness and tensile strength obtained as the weld passes increased from 2 to 4 was traced to better grain refinement, improved particles distribution and fragmentation. However, slight reduction in these properties at 6 passes was observed. Ductile fracture mode was found in all the joints except for joints reinforced with 1.01-1.72 g of SiC that showed evidence of brittle fracture. The specific wear rates of the entire reinforced joints are lower than that of the unreinforced joint. The weldment formed with 0.56 g SiC addition at 4 weld passes exhibited the best combination of properties among the entire weldments.