The Influence of Processing Parameters on Selective Laser Melting of A357 Al Cast Alloy

Selective Laser Melting (SLM) completely melts metal powder with a high-power laser beam to form a metallic part with high density. Currently available alloys used in this cost-effective process include Hastelloys, titanium alloys and steels. Although one of the most important groups of industrial cast alloys with high strength/density ratio and thermal properties, aluminium cast alloys have been less frequently studied in the SLM field. However, since conventional casting and SLM are two completely different techniques, it is not obvious that the SLM procedures and parameters for heat treated alloys can be transferred directly to cast aluminium alloys. The aim of this work is to investigate the effects of SLM and heat treatment parameters on the microstructure and properties of heat-treatable A357 aluminium cast alloy.

A357 aluminium samples were built with varied SLM process parameters. The maximum sample density was achieved by optimising the laser power, scan speed, hatch distance, powder layer thickness and substrate temperature. Based on SEM observations, the SLM process results in a very fine microstructure with small pores. The grain size and Si particle distribution are much finer than in the cast material. Furthermore, small Si particles globularise during solution treatment. Ageing characteristics were determined by plots of the hardness curves. Tensile tests indicate a difference in deformation response of samples built with the tensile axis parallel to the build direction compared to samples built with the tensile axis perpendicular to the built direction. We explain the anisotropy in relation to the directionality of the microstructure. In this regard, the work is expected to lead to optimised SLM process parameters that minimise anisotropic properties in aerospace engine components.