Characterisation of the multiple effects of Sc/Zr elements in selective laser melted Al alloy

Abstract

The widespread application of selective laser melting (SLM) fabricated high performance lightweight Al components is hindered by the available commercial alloys due to their limited mechanical properties and processability. The introduction of Sc/Zr elements to the Al matrix for SLM provides conspicuous benefits, including grain refinement, precipitation strengthening and high thermal stability. In the present study, the multiple effects of Sc/Zr elements in SLM fabricated Al alloy are systematically investigated, using the recently developed Al-Mn-Sc alloy as an example. The application of Sc/Zr elements generated an unconventional heterogeneous grain structure characterised by the alternative growth of columnar-equiaxed grains in the molten pool, which effectively avoided the solidification cracks and alleviated the mechanical property anisotropy issues. The formation of the heterogeneous grain structure is mainly attributed to the precipitation of the primary Al3(Sc,Zr) particles which dependent on the local solidification conditions. The post heat treatment was also conducted to clarify the role of Sc/Zr additions on stress relieve effect and precipitation hardening effect. Moreover, the room temperature and elevated temperature mechanical properties of the SLMed Al-Mn-Sc alloy were also evaluated. The fundamental understanding of the Sc/Zr benefits in the SLM fabricated Al alloy is expected to shed light on future high performance Al alloy development specifically for the additive manufacturing process.