Fusion and friction stir welding of aluminum-metal-matrix composites

Microstructure evolutions and degradations of aluminum-metal-matrix composites during fusion welding were studied and compared with thermodynamic calculations. In fusion welds of Al₂O₃-reinforced composites, the decomposition of Al₂O₃ was observed. In fusion welds of SiC whisker-reinforced composites, the decomposition of SiC to Al₄C₃+Si by reaction with molten aluminum occurred. These phenomena led to unacceptable fusion welds in aluminum metal-matrix composites. Successful welds were produced in the same composites by friction stir welding (FSW). Significant reorientation of SiC whiskers close to the boundary of the dynamically recrystallized and thermomechanically affected zone (TMAZ) was observed. The small hardening in the dynamically recrystallized region was attributed to the presence of dislocation tangles in between SiC whiskers.