Spot Friction Welding Joint Strength Improvement Using Localized Metal Matrix Composite Formation

This study investigates the application of metal particles in spot friction welding (SFW), a semi-solid state sheet metal joining process, to create the localized metal matrix composite (MMC) for the improvement of lap-shear strength. Ancorsteel^® 1000 particles, compressed around the axial center-line of the tool between the upper and lower sheets, was demonstrated to form a localized MMC and effective as the reinforcement particles in aluminum 6111-T4 alloy sheets. Results revealed that the particle MMC in SFW increased the maximum lap-shear by 20%. In the stir-zone, steel particle sizes were significantly reduced due to breaking by mechanical action. Analysis revealed an aluminum-ferrous solid solution formation around the steel particle and aluminum matrix interfaces. In the heat-affected zone along the joint line, steel particles retained their original sizes and reinforced the joint interface. The load deflection curve and cross-section micrographs of the failed lap-shear tensile specimens indicated that, for steel particle MMC samples, the crack path was longer. This was due to a localized MMC forming along the joint interface and was identified as the primary factor responsible for the increase in SFW lap-shear strength.