Laser powder bed fusion of AlSi10Mg: Influence of energy intensities on spatter and porosity evolution, microstructure and mechanical properties

The generation of both spatters and pores during the laser powder bed fusion (LPBF) process has a substantial detrimental effect on mechanical properties. Consequently, eliminating pores is an urgent problem to ensure the quality and yield of fabricated parts. The aim of this study is to evaluate the effect of the critical variables such as laser power (W), linear energy density (J/mm) and volumetric energy density (J/mm(3)) on pore characteristics (diameters and numbers), microstructure and mechanical properties. In addition, this study first demonstrates that the spatter is hypothesized to be an additional cause of porosity, beyond those traditionally understood to be resulting from process parameters or feedstock moisture. In our study, three different types of landed droplets were observed, i.e., hollow droplets, semi-hollow droplets and solid droplets. The hollow and semi-hollow droplets triggered the formation of pores during solidification. The results also revealed that the pores could not be eliminated completely, and the intense spattering resulted in the formation of more pores. Furthermore, the effects of process parameters on pore characteristics and mechanical properties are complex, and it is necessary to consider the combined effects of laser power, linear energy density and volumetric energy density. For the experiments with constant volumetric energy densities of 111.1 J/cm(3), the quantities of pores reduced with a decrease in linear energy density from 0.2 J/mm to 0.15 J/mm, and the ultimate tensile strength increased to 475.18 MPa. When the linear energy density decreased to 0.12 J/mm, the tensile strength decreased to 422.55 MPa. As the result of insufficient linear energy density, some large irregular pores (larger than 100 um) were observed inside the specimen. Besides, for the experiments with constant linear and volumetric energy densities of 0.2 J/mm and 111.1 J/cm(3), the number of pores decreased while the ultimate tensile strength increased with laser power and scanning speed increased simultaneously. The highest ultimate tensile strength exceeded 480 MPa when the laser power was greater than 360 W. (C) 2020 Elsevier B.V. All rights reserved.