In-situ laser surface remelting of laser powder bed fused AlSi10Mg alloy at argon and nitrogen protective gases: Multiscale analysis

Abstract

In the recent decades, laser powder bed fusion (LPBF) of aluminum alloy has been widely used in many fields. However, the poor surface quality, inevitable defects, and limited mechanical performance are obvious obstacles. In-situ laser surface remelting (LSR) is a promising method to give a second opportunity for the defect elimination. In this work, the LSR protective gas (argon and nitrogen) on the surface roughness, porosity, and microstructure of LPBF-fabricated AlSi10Mg alloy are experimentally compared. The nitrogen shows significant superiority in the surface flatness and densification enhancement compared with argon gas. After LSR at nitrogen gas, the average grain size reduces by 8.7 % and the low-angle grain boundaries increases from 70.9 % to 99.7 %. Moreover, a two-dimension mesoscale FEM (Finite Element Method, FEM) model is established to investigate the movement of multi pores inside the molten pool. Attributed to the lower density and dynamic viscosity and larger thermal conductivity, the combination of multi pores is significantly drastic with obvious surface fluctuation during LSR at nitrogen gas. According to the density functional theory (DFT) calculation, the absolute adsorption energies of nitrogen on Al (100) and Al (110) surfaces are generally larger, revealing that the argon gas is easier to be adsorbed on the processing aluminum layer during LSR treatment. Furthermore, the vacancy defects in the aluminum layer play positive roles in the adsorption of gas. This work establishes the importance of the protective gas on the LSR treatment, and provides a multiscale analysis method for the pore evolution.