Microstructural, mechanical and thermo-physical characterization of hypereutectic AlSi40 fabricated by selective laser melting

Abstract

The powder bed additive manufacturing (AM) process Selective Laser Melting (SLM) enables designers and engineers to overcome restrictions of conventional manufacturing technologies. The potential of fabricating complex lightweight structures and processing advanced materials are key features for enhancing the further development of high performance components for space applications.Due to a high specific stiffness and a thermal expansion coefficient very close to electroless Nickel, which is an advantageous optical coating, the hypereutectic aluminum-silicon alloy AlSi40 shows great potential for the manufacturing of optical mirrors for space applications. In prior investigations, Hilpert et al. showed the feasibility to process AlSi40 by SLM. Nevertheless, in order to qualify this material for space applications, the manufacturing process and fabricated samples need to be thoroughly investigated in terms of microstructural, mechanical as well as thermo-physical characterization.We present results of the SLM process development for manufacturing dense AlSi40 samples with a relative density above 99.50 %. The effect of various process parameters, such as hatch distance, preheating and scanning strategy on the formation of defects was investigated by destructive (e.g. OM) and non-destructive (e.g. CT) testing. In addition, the effect of several thermal post-treatments on the AlSi40 microstructure was profoundly analyzed by multiple methods such as OM, SEM and EDX analysis. Moreover, mechanical and thermo-physical testing of manufactured specimens was conducted to provide material characteristics for component design.Concluding, the determined material properties of AlSi40 samples fabricated by SLM were compared to bulk material properties. The gained knowledge and testing data were evaluated in order to identify correlations and dependencies.