EFFECT OF Ni ADDITIONS ON MECHANICAL PROPERTIES AND MICROSTRUCTURE OF THE A356 ALUMINIUM FOUNDRY ALLOY
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In the last years, aluminium producers have reported increasing Ni concentrations in primary aluminium originating from the anodes employed during the electrolytic reduction of alumina. Due to the absence of cost efficient method for Ni removal from the melt, this impurity element may remarkably affect the final quality of downstream products, such as the widely used Al-Si foundry alloys. On the other hand, owing to the thermal stability of Ni-containing compounds, such as Al3Ni and Al9FeNi, Ni as an alloying element may have a positive impact if enhanced mechanical properties at elevated temperature are sought for. This paper investigates the effect of three different N i additions (0.5, 1 and 2 wt.%) on the high-temperature tensile properties of the commercial purity unmodified A356 (Al-7 wt.% Si-0.3 wt.% Mg) aluminium foundry alloy. As-cast and T6 heat-treated tensile samples, obtained by permanent mould casting, have been tested at 235 °C. Fracture profiles and surfaces have been observed via Optical and Scanning Electron Microscopy to analyse the mechanism of failure.