Aluminium matrix composites (AMCs) by DMLS

Abstract

Many materials have been processed successfully and many reports are available in literature on the direct metal laser sintering (DMLS) of iron, steels, superalloys, Ti and Al alloys. Recently, also processing of composite materials has attracted interest due to the potential of the process in freeform fabrication of intricate articles in a reduced production cycle. In this paper are summarized the main results for the fabrication of AlSiMg/SiC and AlSiMg/MgAl2O4 composites by DMLS. The starting metal and ceramic powders have been simply mixed using a ball milling system. Then processing has been carried out in an Ar atmosphere using different laser energies at different scanning speeds to fabricate geometric regular samples with densities near to the theoretical ones. The resulting composites have been investigated in terms of microstructure by XRD and by optical microscopy, and in terms of hardness. effects of process parameters on the density of metal matrix composites built by DMLS. In this study, an investigation about the possibility of fabricating aluminum-based composites by DMLS, using an EOS GmbH machine, is presented. The aluminum alloy is an AlSiMg alloy, containing 10% Si and 0.3% Mg, thus similar to some casting alloys like A360. This alloy has a high fluidity of the liquid phase that makes easier the preparation of pore-free samples. Moreover, if silicon carbide is the second phase, a high silicon content is known to limit (or avoid) the formation of the aluminum carbide Al4C3, which is generally detrimental to mechanical properties due to its high sensitivity to reaction with water. Different reinforcing phases were used: in particular submicrometric SiC and nanometric MgAl2O4 powders. In order to prepare the starting materials for the composites, aluminum alloy powders were mixed with the ceramic phase. Small grain size ceramics were chosen in order to avoid problems and inhomogeneity during the building of the samples, and in particular for the Mg spinel in order to take advantage of the unique mechanical and physical properties at the nano-scale even employing a little quantity of reinforcements. The composites obtained were firstly characterized regarding density and porosity, since the first concern with DMLS is the optimization of the parameters needed to obtain a dense material. In a second time, compositions were checked, to see if reactions between matrix and reinforcements occurred, and then mechanical properties were estimated through the evaluation of the composites hardness.