Influence of the addition of rare earth metals and of overheating on microstructure and mechanical properties of aluminium alloy A319

Abstract

This study concerns the influence of certain metallurgical factors, like the addition of a mixture of rare earth metals (mischmetal) and of overheating, on the microstructure and the tensile properties of alloy A319-2 (Al-Si-Cu with 0.4, 0.8 and 1.2% iron) The new phase linked with mischmetal has a needle - and/or platelet - shape as the β-iron phase and impedes the flow of the liquid metal during casting, thus creating porosity. The different types of particles present in the microstructure remain after the T6 thermal treatment. In the alloys containing 1.2% iron, the length of the β phase and mischmetal particles is slightly smaller than in the alloys with 0.4% Fe or 0.8% Fe, after the addition of 5% mischmetal and overheating at 950°C. This explains the better tensile elongation of the 1.2%Fe-5% mischmetal alloy cast at 950°C instead of 750°C. UTS and yield strength are decreased by the addition of mischmetal but are slightly improved by overheating. Overheating at 950°C decreases the yield strength only in the 1.2% Fe-0% mischmetal alloy.