Heat treatment T4 and T6 effects on the tribological properties of sillimanite mineral-reinforced LM30 aluminium alloy composites at elevated temperatures

Abstract

The present study investigates effect of heat treatment on wear and friction behaviour of sillimanite/LM30 aluminium matrix composites at elevated temperatures (50–300 °C). The composites were prepared using a stir-casting process. Composites were reinforced with 3–15 wt.% sillimanite particle sizes of fine (1–20 μm):coarse (75–106 μm) in the ratio of 1:3, 1:1 and 3:1, respectively. Next, the composites were subjected to T4 and T6 heat treatment. For T4 heat treatment, composites were heated at 550 °C for 1 h, water quenched and naturally aged (at room temperature) for 480 h. Further, for T6 heat treatment composites were artificially aged at 200 °C for 4 h and air cooled. Hardness of composites improved with increase in particle weight percentage and increases in the ratio of fine particles in the mix. Maximum improvement in hardness was observed for 15 wt.% T6 heat-treated composites with fine:coarse in the ratio of 3:1. The addition of sillimanite particles improved wear resistance and coefficient of friction of the composites. Wear and friction analysis revealed that beyond 200 °C, wear behaviour of composites changed from mild to severe. Further, the heat treatment of composites improved wear resistance and coefficient of friction. Wear rate and friction coefficient of T6 heat-treated 15 wt.% composite with fine:coarse as 3:1 at 200 °C decreased by 70% and 52%, respectively. X-ray diffraction of wear tracks and wear debris of T6 heat-treated composites revealed the formation of intermetallics and oxides on the wornout surface of the composites. Scanning electron microscopy analysis of wear tracks and debris revealed that at elevated temperatures, abrasive and adhesive wear was dominant for the material removal mechanism. The developed composites exhibited nearly wear behaviour similar to that of grey cast iron used in brake rotors. Thus, sillimanite/LM30 aluminium matrix composites provide a suitable substitute to replace heavy grey cast iron components used in automobile industry.