Selective laser melting of rare earth element Sc modified aluminum alloy: Thermodynamics of precipitation behavior and its influence on mechanical properties

The interest of selective laser melting (SLM) Al-based alloys for lightweight applications, especially the rare earth element Sc modified Al-Mg alloy, is increasing. In this work, high-performance Al-Mg-Sc-Zr alloy was successfully fabricated by SLM. The phase identification, densification behavior, precipitate distribution and mechnical properties of the as-fabricated parts at a wide range of processing parameters were carefully characterized. Meanwhile, the evolution of nanoprecipitation behavior under various scan speeds is revealed and TEM analysis of precipitates shows that a small amount of spherical nanoprecipitates Al3(Sc,Zr) were embedded at the bottom of the molten pool using a low scan speed. While no precipitates were found in the matrix using a relatively high scan speed due to the combined effects of the variation of Marangoni convection vector, ultrashort lifetime of liquid and the rapid cooling rate. An increased hardness and a reduced wear rate of 94 HV0.2 and 1.74 × 10−4 mm3N-1 m-1 were resultantly obtained respectively as a much lower scan speed was applied. A relationship between the processing parameters, the surface tension, the convection flow, the precipitation distribution and the resultant mechanical properties has been well established, demonstrating that the high-performance of SLM-processed Al-Mg-Sc-Zr alloy could be tailored by controlling the distribution of nanoprecipitates.