Study on the mechanism of correlation between surface quality and tissue properties of Ti6Al4V alloy formed by selective laser melting

Abstract

This paper investigates the correlation between the surface quality and the cross-sectional quality, microstructure, internal defects, and mechanical properties of specimens formed by selective laser melting (SLM) under different scanning speeds and scanning intervals. Therefore, different machining parameters were chosen to prepare titanium alloy specimens by SLM technique. The surface morphology of the specimens was characterized using a light microscope, and the surface quality, microstructure, internal defects, and deep connection of the mechanical properties of the specimens formed under different parameters were investigated. In addition, numerical simulation of the melt pool morphology under different scanning speeds was used. The results show that there is a strong correlation between the surface quality of the specimen and the section quality and mechanical properties. When the scanning speed is 350 mm/s, the surface roughness is 14.7 μm, the density is 99.99%, the tensile strength and yield strength are 1209 and 1151 Mpa respectively, and the surface quality, cross-sectional quality and mechanical properties all tend to deteriorate as the scanning speed increases. When the scanning interval is 0.11 mm, the mechanical properties of surface quality and cross-sectional quality are optimal, the surface roughness is 14.5 μm, and the density reaches 99.99%, at this time, the microscopic needle martensite α′ phase is uniformly distributed and refined, and its mechanical properties are optimal, the tensile strength is 1239 MPa, and the internal hole defects are less. Numerical simulations of a single track melt pool show that the depth of depression caused by the recoil pressure is larger and the melt pool is deeper when the scanning speed is 350 mm/s. Therefore, it has better fluidity and ductility. Simulation results of the double tracks show that when the scanning interval is 130 μm, a large amount of incompletely melted powder at the midline of the double track does not lap well, which leads to the formation of pore defects inside the specimen. The above simulation results are highly consistent with the surface quality of the specimens during the experiments, which provides a guide to analyze the connection between the melt pool evolution and the Ti6Al4V molding quality.