Effect of a T6 aging treatment on the corrosion behaviour of in-situ AlxNiy reinforced AA6061 composite

Abstract

Abstract In-situ AlxNiy reinforced aluminium matrix composites (AMCs) were produced by stir-casting route by adding 5, 10 and 15 wt% (wt. %) Ni to AA6061 alloy. The as-cast samples were subjected to a T6 ageing treatment at 180 °C for 4 h after solutionizing treatment at 535 °C for 1 h. The density, porosity, microstructure, hardness, and corrosion behaviour of the as-cast and heat treated AA6061 and the AMCs were evaluated. All the castings were found to be sound with low porosity. Porosity in heat treated samples was lower than the porosity in the as-cast samples. This trend was reversed only in AMC containing 15 wt% Ni. Optical microscopy studies revealed that in-situ formed AlxNiy was distributed along the dendritic arms, both in the as-cast as well as in the heat treated AMCs. The distribution became non-homogeneous and coarse with increase in Ni content and with age hardening. Hardness increased with increase in Ni addition till 10 wt% Ni beyond which it decreased due to the coarse distribution of AlxNiy in the matrix. The artificially aged castings showed higher hardness compared to their as-cast counterparts. The corrosion current (icorr) increased while the polarization resistance (Rp) decreased with the increase in Ni addition in the AMC, in the as-cast as well as in the age-hardened condition. The age-hardened samples showed poor corrosion resistance than the as-cast composites. This indicates that the coarse non-homogeneous distribution of in-situ AlxNiy had a detrimental effect on the corrosion performance of the AMCs.