Friction Stir Welding of Metal Matrix Composites

Friction Stir Welding (FSW) is a solid-state joining process developed by TWI. The large axial forces associated with this process are typically cited as one of the major obstacles to its widespread application. The primary objective of this research is to quantify the reduction of axial force through use of diamond coatings of FSW tools. Results of welds for coated and uncoated tools on Al 6061 are compared. The goal is to produce friction stir welds using the diamond-coated tool that are comparable in quality to those performed using conventional tool materials, but with an appreciable reduction in tool wear and/or axial force. The secondary objective of this research is to parameterize FSW of Al 6061 reinforced with 17.5 percent SiC particles, a superabrasive composite material valued for its high strength to weight ratio. A range of acceptable process parameters for the joining of this material is established. Since tool wear is a limiting factor in the joining of composites, tool wear is periodically monitored and quantified using an optical comparator.