An SLM-processed Er- and Zr- modified Al–Mg alloy: Microstructure and mechanical properties at room and elevated temperatures

Abstract

The elements of Sc and Zr have been used to modify the Al–Mg alloys to improve the Selective Laser Melting (SLM) processability and enhance the mechanical properties. However, these alloys are very expensive due to the addition of Sc. In this study, Er is used as a cost effective substitute for Sc in an Al–Mg alloy processed by SLM and the effects of Er in combination with Zr on microstructure and mechanical properties are investigated. It is found that with optimized laser parameters, Er and Zr result in excellent grain refining, forming a bimodal grain structure with fine equiaxed grains (∼0.8 μm) and columnar grains (2–10 μm). The grain refinement is mainly attributed to the heterogeneous nucleation effect and the grain boundary pinning effect of the Al3Er and Al3(Er, Zr) particles. The as processed condition shows a large amount of Al3Er and Al3(Er, Zr) precipitates 5–50 nm in size with L12 structure, and additional post-SLM aging treatment is not required as it does not provide further benefit in hardness. The Al–Mg–Er–Zr alloy exhibits a room temperature tensile strength of 340 MPa and 329 MPa in x and z directions respectively, as well as a 300 °C tensile strength of 107 MPa and 102 MPa in x and z directions, making this alloy an attractive and economical candidate for applications at elevated temperatures.