Abstract:Friction stir welding (FSW) is a solid state joining technique developed to join high strength aluminum alloys and various ceramic reinforced metal matrix composites (MMCs). FSW produces sound welds in MMCs without any deleterious reaction between reinforcement and matrix. The present work focused on the effect of FSW parameters on the tensile strength of Al-B₄C composite joints. The central composite design of four factors and five levels was used to control the number of experiments. A mathematical model was developed to analyze the influence of FSW parameters. The results indicated that the joint fabricated using rotational speed of 1000 r/min, welding speed of 1.3 mm/s, axial force of 10 kN and the reinforcement of 12% showed larger tensile strength compared with the other joints. The developed model was optimized to maximize the tensile strength using generalized reduced gradient method. The metallographic analysis of the joints showed the presence of various zones such as weld nugget (WN) zone, thermo mechanically affected zone (TMAZ) and heat affected zone (HAZ). The substantial grain refinement of aluminum matrix as well as significant size reduction of B₄C particles was observed in the weld nugget. TMAZ was plastically deformed, thermally affected and exhibited elongated aluminum grains.

Key words: friction stir welding; metal matrix composites; boron carbide; joint; mechanical properties