Welding of AA6061-(Al2O3 )p composite: effect of weld process variables and post-welding heat treatment on microstructure and mechanical properties

Abstract

Metal–matrix composites reinforced with Al2O3 particles combine the properties of the matrix (ductility and toughness) with the ceramic properties of the reinforcements (high strength). However, their wide application as structural materials requires a proper development of their joint process. The present work describes the results obtained from microstructural (optical and scanning electron microscopy) and mechanical evaluation (hardness and tensile tests) of the welded aluminium–matrix composite (AA6061) reinforced with 10% and 20% volume fraction Al2O3 particles (W6A10 and W6A20, respectively) using the MIG (metal inert gas) welding process and ER5356 (AlMg5) as filler material. A characteristic of the welds carried out in composites is that the size of the melt pool is wider than in the unreinforced materials, for the same welding conditions. This is caused by the lower thermal conductivity of the composites. Furthermore, composites act as an insulator reducing the cooling rate of the bath. The thermal effect of welding on different types of joints results in a loss of the mechanical properties in the heat affected zones (HAZ). These properties can be recovered with post-welding heat treatment.