The role of the layer thickness on the surface integrity of LPBF AlSi7Mg after turning

Abstract

Laser powder bed fusion (LPBF) is an additive manufacturing process used to fabricate aluminum alloy complex structures for the aerospace and automotive industries. By optimizing the printing and subsequent heat treatment parameters, it is possible to achieve physical and mechanical properties comparable to those of cast and wrought aluminum alloys. The influence of the printing parameters on the aluminum alloy mechanical properties is well documented, but their effect on the machinability has not been extensively studied, yet.

In this regard, the paper aims to investigate the effect of the layer thickness adopted in LPBF on the machinability of the aluminum alloy AlSi₇Mg. Three sets of cylindrical samples were printed with different layer thicknesses (20, 25, and 30 µm), followed by a T6 heat treatment. Then, the cylinders were machined at fixed cutting parameters while recording the cutting forces. Afterward, the machined surface roughness and defects were analyzed.

Results show that increasing layer thickness improves the overall machining performance, with a decrease of more than 70% of the surface roughness and forces when printing with the highest layer thickness. To explain such behavior, microstructural analyses, including melt pool and grain distribution, precipitate type, and morphology, were carried out, proving that an increased layer thickness promoted the formation of silicon precipitates, which, in turn, improved the alloy’s machinability.