Effect of tool material, profile and D/d ratio in friction stir welding of aluminium metal matrix composites

Friction stir welding, a novel semi-solid state welding process, has been constantly evolving technology since 1991. In this work friction stir welding was carried out on aluminium metal matrix composites reinforced with SiC and ZrB₂. The influence of tool profile and material on the strength of weldment was studied. Plain pentagon, plain tapered and threaded cylinder tool made of materials such as OHNS, HCHCr, and H13 with varying D/d ratios were used. The friction stir welded specimens were subjected to mechanical and metallurgical characterization. Threaded cylinder profiled tool made of H13 steel with a D/d ratio of 2 yielded weld joints of highest strength. Weld zone microstructure of the Al-10% ZrB₂ MMC and Al-10% SiC welded using H13 threaded cylinder tool exhibited considerable grain refinement with the precipitates homogeneously distributed. (paper)