Effect of Heat treatment parameters on the tribological performance of LM26/graphite/fly ash hybrid aluminium matrix composites using Taguchi-TOPSIS optimization

Hybrid aluminium matrix composites (HAMMCs) are of interest for lightweight components requiring improved resistance to wear and friction. The present study investigates the effects of solution treatment temperature, holding time and cooling method on the tribological behaviour of stir-cast LM26/graphite/fly ash hybrid aluminium matrix composites. A Taguchi L27 orthogonal array was used to evaluate solution treatment temperatures of 450, 500 and 550 °C, holding times of 2, 4 and 6 h, and furnace cooling, air cooling and water quenching. Hardness, wear rate and coefficient of friction (COF) were considered as response characteristics. TOPSIS was used for multi-response evaluation, and analysis of variance (ANOVA) was used to assess the contribution of the heat treatment parameters. Scanning electron microscopy (SEM) was used to examine reinforcement distribution in the matrix. The measured hardness ranged from 42.3 to 51.2 BHN, while the wear rate and COF ranged from 0.000667 to 0.000750 mm 3 /min and 0.4002 to 0.4501, respectively. The experimental results showed that hardness increased from 42.3 to 51.2 BHN, while wear rate and coefficient of friction decreased from 0.000750 to 0.000667 mm 3 /min and from 0.4501 to 0.4002, respectively, across the investigated conditions. Experiment 18, corresponding to 500 °C, 6 h and water quenching, gave the highest TOPSIS relative closeness value (0.8933). Factor-level analysis identified 550 °C, 6 h and water quenching (A3B3C3) as the optimum combination within the investigated design space. Temperature had the greatest influence on wear rate, coefficient of friction and the TOPSIS grade, whereas cooling method had the greatest influence on hardness. These results show that the selected heat treatment conditions substantially affected the combined hardness–wear–friction response of the hybrid composite under the investigated dry-sliding conditions.