Tribocorrosion Behaviour of Sustainable Seashell-Derived Silicon Reinforced AZ91 Magnesium Composites: Interplay between Wear, Electrochemical Degradation and Interface Stability

Abstract AZ91 magnesium alloys are interesting for their lightweight structural and biomedical applications, but their service life is reduced when mechanical sliding and chloride corrosion are combined. This kind of attack (tribocorrosion) erodes much more than wear or corrosion alone. The AZ91 was reinforced with Si particles recovered from waste seashells, and the influence of Si on wear, electrochemical corrosion, and interfacial stability of the Si-particle matrix was investigated in this work. Shell waste was subjected to calcination and reduction to obtain seashell-derived silicon (SDSi) particles, which were then added to the melt at 3, 6 and 9 wt% by stir casting. The microstructure, phase content, density, microhardness, static electrochemical testing, dry-sliding wear testing, and combined tribocorrosion testing were performed in 3.5 wt% NaCl. The composite with 6 wt% gave the best overall response. The microhardness value was approximately 102 HV, the corrosion current density decreased from ~ 95 to 34 µA cm − 2, and the dry sliding wear rate decreased by almost 58% compared with the base alloy. The open-circuit potential of the 6 wt% composite was more stable under sliding conditions during tribocorrosion, and the synergy between wear and corrosion was reduced by over 50% compared to AZ91. The advantages were reversed at concentrations above 6 wt%, due to the formation of new galvanic sites and weak interfaces in particle clusters. The surfaces of the wear and tribocorrosion parts were analysed, and it was found that the composite exhibited a transition from deep AZ91 delamination and pitting to shallow abrasion and a more protective tribolayer. The findings reveal that if the reinforcement remains well dispersed and well bonded, a low-cost reinforcement derived from waste can enhance the durability of AZ91 under aggressive sliding contact.