The intrinsically quasi-isotropic tensile properties of as-fabricated Al-Mg-Si-Sc-Zr alloy produced by selective laser melting

Abstract

Mechanical anisotropy is among the most concerned properties for selective laser melting produced metals, such as steels and titanium alloys, but is rarely investigated for high-strength Al alloys. In this study, crack-free high-strength Al-Mg-Si-Sc-Zr was prepared by selective laser melting. Systematical tensile tests revealed that Al-Mg-Si-Sc-Zr has intrinsically quasi-isotropic tensile properties. Uniform elongations in horizontal and building directions are comparable and the difference between the two tensile strengths is less than 3%. Al-Mg-Si-Sc-Zr exhibits bi-modal microstructures consisting of 39 vol% equiaxed ultrafine grains and 61 vol% columnar grains. The presence of equiaxed ultrafine grains interrupts epitaxial growth of columnar grains and thus prevents the development of the fiber texture intensity. The tiny grain size and Mg2Si stripes on grain boundaries make equiaxed ultrafine grains brittle and susceptible to cavity nucleation and intergranular cracking. A weak fiber texture and randomly orientated cracking-prone equiaxed ultrafine grains endow Al-Mg-Si-Sc-Zr with intrinsically quasi-isotropic tensile properties.