Effect of post welded heat treatment on tungsten inert gas welded Al6061-SiC composites

Metal matrix composites (MMCs) of aluminum alloys (6061) reinforced with silicon carbide (SiC) were prepared with 8 and 10 wt.% of SiC through a stir casting process, with an average size of 25 μm. The composites of identical compositions were welded using single-pass tungsten inert gas (TIG) welding, using an ER5356-grade filler material. The hardness and tensile strength of the weld zone in the as-welded condition were measured. The samples were then subjected to age-hardening treatment at two different temperatures (100 and 200°C) and different holding times. The peak hardness values were recorded under both temperature conditions. The tensile strength for every different condition was also measured and compared with the values of the as-welded condition. The results indicated that age-hardening treatment had a significant influence on the improvement of the hardness and the tensile strength of the samples. The microstructure of the fractured surface in the as-welded and age-hardened specimens was observed under a scanning electron microscope (SEM), and the failure modes were analyzed. The pattern of the failure showed a mix of both brittle and ductile nature. The microstructure of the as-welded samples showed a relative distribution of SiC in the matrix. The distribution was not uniform throughout the matrix and seemed to have preferably distributed around the grain boundaries. The microstructures observed through the SEM could not bring out the fine precipitates that could have resulted from age hardening because of its limited resolution. However, the presence of precipitates was verified through X-ray diffraction studies.