Abstract
Three A356 aluminium alloy melts with different oxide contents were produced by mixing alloy turnings with ingot material. The melts had a constant hydrogen level and were cast in a step mould steel die. The resulting casting porosity was characterized using the Archimedes’ method and image analysis. Melt quality was accessed using a Porous Disc Filtration Apparatus (PoDFA) and the Reduced Pressure Test (RPT). It was shown that oxide additions lead to higher amounts of fine structured oxide films resulting in an increase of the fraction of small pores. Shrinkage porosity with its inherent partially elongated and interdendritic pore morphology was predominant. Ultimate tensile strength (UTS) and elongation from thin and thick sections in the step castings deteriorated with increased oxide content; UTS decreased from 3-18 % and elongation from 18-38 % with oxide additions as the section thickness increased. The melt cleanliness analyses from PoDFA were consistent with the oxide additions. Keywords: porosity, oxides, bifilm, mechanical properties, A356 alloy
