High power laser powder bed fusion of AlSi10Mg alloy: Effect of laser beam mode

Abstract

High power laser powder bed fusion (HP-LPBF) is a burgeoning additive manufacturing technology for the high-efficiency and high-accuracy build of metallic parts. However, studies about the effect of laser beam mode on build quality is still insufficient. In this paper, both a 2 kW multi-mode fiber laser and a 2 kW Gaussian mode fiber laser are used for the HP-LPBF of AlSi10Mg alloy. Firstly, the relative density (RD) of the HP-LPBF samples has been studied for parameter optimization. The RD of the samples built with the multi-mode laser beam (hereafter called as Multi-mode sample) first increases and then remains stable with the increase of laser energy density Ev. When Ev is no less than 50 J/mm3, the RD of the Multi-mode sample is higher than 99.5%. In contrast, the RD of the samples built with the Gaussian mode laser beam (hereafter called as Gaussian sample) first increases and then decreases with the increase of Ev, and the highest RD is just 95.87 ± 0.2% at the Ev of 50 J/mm3. Based on this, the Multi-mode sample and Gaussian sample built with the same parameters (Ev=50 J/mm3) are chosen as the typical contrast samples for further studies of surface quality, microstructure and tensile property. The results show that the typical Multi-mode sample presents a flatter surface and a lower surface roughness compared with the Gaussian sample. The phase composition of both the two kinds of samples consists of α-Al matrix and eutectic Si. However, the solidification microstructure varies with laser beam mode. The Multi-mode sample presents a columnar solidification microstructure with a strong< 100 > texture along the build direction. In contrast, the solidification microstructure of the Gaussian sample is a mixture of equiaxed grains and short columnar grains. The crystallographic orientations of the two kinds of grains are multifarious, leading to a much weaker texture. The tensile strengths and elongation of the Multi-mode sample are significantly better than those of the Gaussian sample. The effect mechanisms of the laser beam mode on relative density, surface quality, microstructure and tensile property have also been revealed.