Investigation of T4 and T6 heat treatment on the wear properties of sillimanite reinforced LM30 aluminium alloy composites

In the present work, an attempt has been made to study the effects of heat treatment on the dry sliding wear properties of sillimanite reinforced LM30 aluminium matrix composites. Stir casting process was used for the processing of the composites. Composites with two different particle sizes (fine 1-20 mu m and coarse 75-106 mu m) and different weight ratio (3-15 wt% in the step size of 3 wt%) were fabricated. Further, the fabricated composites were subjected to the heat treatment as per T4 and T6 process. The composites were heated (at 540 degrees C), held at that temperature for 0.5-2 h and quenched in water. For T4, the composites were subjected to natural aging of 10-30 days at room temperature and for T6, composites were artificially aged by reheating to a temperature of 150-250 degrees C, holding there for 1-5 h, followed by air cooling. Hardness testing revealed that the composites subjected to T6 heat treatment exhibited superior hardness in comparison to normal composites and T4 heat treated composites. Further, wear analysis revealed that heat treatment of the composites affected the wear properties of the composites. Maximum improvement in the wear rate was observed for T6 heat treated composites. Also, the coefficient of friction of T6 heat treated composites was lower than other composites. Finally, SEM analysis revealed that the surface damage observed for T6 composites was lesser in comparison to other. In the initial period of wear abrasive wear was dominant and with increase in the sliding distance adhesive/delamination wear mechanism was dominant. Therefore, T6 composites revealed a superior combination of wear properties, and found to be in close comparison to grey cast iron used in the brake drum applications. Hence, 15 wt% reinforced T6 composites can be used as an alternate material for brake drum applications.