Microstructure and mechanical properties of friction stir welded AA6063–B4C metal matrix composites

The weldability, microstructure evolution and mechanical properties of an AA6063 aluminium alloy and of two composites with AA6063 matrix reinforced with 6 and 10.5 vol.% B4C during friction stir welding are investigated. A joint efficiency higher than 60% was obtained and increased to over 80% after artificial ageing. The B4C particles size and shape were not affected by the welding process and the particle distribution in the matrix was kept uniform in the weld zone. Evolution of the aluminium grain structure from coarse grains in the base material to the refined, equiaxed grains in the weld centre is described. The microhardness profiles of various B4C concentration materials were measured in both as-weld conditions and after post-weld heat treatments. Other microstructure changes of Al–B4C MMCs after welding and heat treatment are also reported.