Particle agglomeration and fracture in MA 956 and MMC friction joints

Changes in the particle characteristics produced during friction joining of iron–based MA 956 and aluminium alloy 6061/Al2O3 (W6A.lOA–T6) material are investigated. Large irregularly–shaped particles are formed at the bondline in MA 956/MA 956 joints while particle fragmentation is observed in MMC/MMC joints. It is suggested that fluid flow promotes the retention of agglomerated (Y2O3, Al2O3, Ti(CN)) particles and fractured Al2O3 particles at the bondline regions in MA 956/MA 956 and MMC/MMC joints. There was excellent correspondence between numerically calculated fluid flow patterns in Al/Al friction joints and the movement of reinforcing Al2O3 particles in actual friction welded joints. In particular, Al2O3 particles were transferred from the location near the joint periphery towards the component centreline when MMC wires were inserted in an alloy 6061–T6 substrate prior to 6061/6061 friction joining.