Abstract: In order to clarify the reliability of laser energy density as a basis for selective laser melting (SLM) process optimization, the effect of volume energy density (process combinations of different laser powers, scanning speeds and scanning spacing) on the microstructure and properties of SLM-formed alloy by means of an orthogonal experimental design was investigated. The AlSi12 alloy was fabricated by SLM forming technology, and the densities, melt pool boundary, microstructure and mechanical properties of the alloy were characterized and investigated by optical microscope, scanning electron microscope and room temperature tensile tests. The results show that under the same volume energy density, with the increase of the laser power, the melt pool deepens, the proportion of equiaxed grains in the heat-affected zone at the edge of the melt pool decreases, and the microstructure of the fine grain zone gradually coarsens; while with the increase of the scanning speed, the melt pool broadens, the proportion of equiaxed dendrites in the fine grain zone increases, the microstructure of the coarse grain zone refines, and the fine Si particles in the heat-affected zone gradually increase. The volume energy density cannot be used as the only influencing factor for the judgement of quality of the shaped parts. The laser power has the greatest influence on densification, tensile strength and yield strength, while the scanning speed has the greatest influence on elongation. The mechanical properties of the specimens are optimal at the laser power of 300 W, scanning speed of 1200 mm/s and scanning spacing of 60 μm, with the tensile strength of 447.1 MPa, yield strength of 433.7 MPa and elongation of 7.6%.

Key words: laser selective melting, AlSi12 alloy, energy density, orthogonal experiment, mechanical properties