Structure and properties of Al-Mg-Si alloys with Zr and Sc additions produced by melt spinning and twin rolling casting techniques

Abstract

Aluminium alloys with 1 wt.% Mg, 0.6 wt.% Si and 0.5 wt.% Zr, or 0.5 wt.% Zr + 0.2 wt.% Sc additions were cast using different techniques such as: conventional stationary mould casting, twin rolling and melt spinning. Microstructure studies have shown that a significant grain refinement down to 20 μm was obtained in the alloy containing 0.5 % Zr + 0.2 % Sc cast to a copper mould due to the presence of Al3(Zr, Sc) primary particles. Columnar grains near the surfaces and equiaxial ones in their central part were observed in strips obtained by the twin rolling method, while the ribbons of thickness 70-100 μm, cast using melt spinning, revealed equiaxial grains of an average diameter of 2-3 μm. The additions of Sc and Zr brought about a small increase of microhardness only in the mould cast alloys and strips while no changes in microhardness have been observed in alloys prepared using various casting techniques. The alloys produced by both unconventional casting techniques were annealed at the temperature range of 400-540°C, which resulted in the precipitation of either Al3Zr or Ab(Zr, Sc) phases from the Al solid solution in the form of spherical (about 10 nm large) particles as well as an additional microhardness increase up to about 130 HV for the AlMg1Si0.6Zr0.5Sc0.2 alloy.