Effect of thermochemical silicon diffusion and age hardening on the mechanical and tribological properties of commercial grade aluminium

Abstract

Abstract Commercially available pure aluminium is an alloy with Si, Cu and Mg impurities lacking in strength and surface hardness compared to its conventional alloys due to small quantity of alloying elements. This study investigates the property alteration with a process of high temperature thermochemical diffusion of silicon by packing commercially available silicon powder of 80–100 micron size, and application of age hardening treatment. Mechanical properties (ultimate tensile strength, %elongation, microhardness and impact strength) of 3 material conditions (as bought, homogenized and Si treated & age hardened) were compared. Microstructure was characterized using SEM combined with energy-dispersive spectroscopy (EDS) to develop a relationship between material composition and failure modes. Homogenization improved elongation and impact resistance, whereas silicon treatment followed by aging increased tensile strength, microhardness, impact energy, and wear resistance but reduced elongation. Wear resistance of aluminium improves many folds after the silicon pickup and age hardening. Homogenization results in 95% increase in absorbed impact energy compared with the as-received material, whereas the silicon-treated condition shows a further increase by 8%. Microstructure of the polished and etched specimens show dendritic segregation in as received condition and coarser grains in heat treated conditions. Wear study demonstrates wear resistance improvement by 350% in silicon-treated and age hardened specimen whereas homogenised reflects 125% improvement over as received specimen. SEM of the worn specimens show extensive damage in untreated condition whereas treated specimens show smoother and more uniform surface.