Investigation and optimisation of tribological performance for AZ31 Mg hybrid composite under the effect of cryogenic treatment

Magnesium (Mg)-based alloys are considered promising candidates owing to their low density and high strength-to-weight ratio; however, they exhibit poor tribological performance. In this study, AZ31 Mg hybrid composites were synthesised through an argon-controlled stir casting process using 10 wt.% ZrO₂ and 2 wt.% seashell powder (SSP) as reinforcements. Furthermore, the fabricated composites were subjected to cryogenic treatment at −196°C to enhance their tribological properties. Microstructural characterisation using scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirmed the uniform distribution of reinforcements within the matrix, with no formation of undesirable intermetallic phases. Dry sliding wear tests were conducted using a pin-on-disc apparatus by varying key input parameters. A Taguchi-assisted Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) approach was employed to determine the optimal conditions for minimising wear rate (WR) and co-efficient of friction (COF). The experimental results revealed that a load (L) of 9.81 N, sliding velocity (V) of 2.82 m/s, and sliding distance (D) of 1500 m yielded the lowest WR and COF. Analysis of variance indicated that load and sliding distance were the most significant factors influencing the tribological performance. Worn surface morphology showed the presence of oxide layers, microcracks, and dominant abrasive wear mechanisms.