Optical surface generation on additively manufactured AlSiMg0.75 alloys with ultrasonic vibration-assisted machining

Additive manufacturing technology provides a feasible solution to directly manufacture optical components with complex functional structure. However, the poor surface quality and low relative density result in the limitation on its rapid application. In order to overcome the above shortcomings, process optimization and ultrasonic elliptical vibration-assisted machining (UEVAM) were used in the fabrication of optical surfaces on selective laser melted (SLM) AlSiMg0.75 alloy. The optimised energy density in the SLM process was identified ranging from 65 to 130 J/mm3 with the highest achievable relative density of 99.6 %. Post-processing heat treatment changed the cellular/dendritic microstructure of as-built samples to an α-Al matrix embedded with Si particles, which reduced the microcutting forces by 27.67 % and improved the machined surface roughness (Ra) by 8.7 % during conventional microcutting. In contrast, the UEVAM process is capable of further improving the surface quality from 11.03–5.1 nm Ra, without heat treatment. It is also evident that poor machined surface quality was attributed to the formation of oxide particles during SLM. Chip morphology analysis and finite element method simulations revealed the benefits of UEVAM in tackling the issue of precipitation and extended our understanding of the applications of UEVAM.