Influence of surface finishing and heat treatment on the dry sliding behaviour of the powder bed fusion-laser beam (PBF-LB) processed A357 Al-Si-Mg alloy, anodised by electrochemical oxidation (ECO)

This work focuses on the reciprocating dry sliding behaviour of PBF-LB processed A357 (AlSi7Mg0.6) anodised by Electrochemical Oxidation (ECO). This surface treatment derives from Plasma Electrolytic Oxidation (PEO) but minimises its disruptive plasma discharge effects. The tribological behaviour of the system was investigated both at room temperature and at 200 °C by ball-on-disk tests against Al 2 O 3 balls, considering the influence of: (i) substrate surface finishing before ECO (unpolished vs. pre-polished by grinding) and (ii) an optimised rapid solution and aging heat treatment (T6R) carried out on A357 to improve its tensile properties in terms of ductility-strength trade-off. Polishing the A357 substrate after printing and before ECO improves the wear behaviour of ECO layers at room temperature by improving thickness and compactness of the coating, even though it slightly increases friction due to destabilisation of low shear transfer layers. At 200 °C, the anodised alloy performance is dominated by thermal damage of the ECO coating and substrate softening effects, hence pre-polishing did not improve the tribological behaviour. Therefore, pre-polishing can be excluded from the processing cycle for PBF-LB components intended for operation at high temperature. T6R does not significantly affect the microstructure and micromechanical properties of the anodic layer and hence its tribological behaviour, both at room T and at 200 °C. Therefore, T6R can be excluded from the processing cycle if tribological performance issues dominate over tensile requirements for the reference application. • Reciprocating dry sliding both at room temperature and at 200 °C (ball-on-disk vs. Al 2 O 3 ) • Anodising above dielectric breakdown potential by electrochemical oxidation (ECO) • Influence of substrate surface finishing before ECO + rapid solution and aging (T6R) • Pre-polishing beneficial at room temperature, not useful at high temperature • T6R does not affect tribological behaviour both at room temperature and at 200 °C.