On the role of additive manufacturing, heat treatment and machining on the microstructural evolution and corrosion behaviour of AlSi9Cu3(Fe) alloy

Laser Based Powder Bed Fusion for Metal (PBF-LB/M) is an additive manufacturing (AM) technique capable of producing geometrically complex, high-performance components. Among the aluminium alloys suitable for PBF-LB/M yet underexplored, AlSi9Cu3(Fe) stands out for its high strength-to-weight ratio and corrosion resistance. While the overall characteristics of AlSi9Cu3(Fe) are firmly established for cast products, studies on its mechanical performance and corrosion behaviour after the PBF-LB/M process and subsequent heat treatments remain scarce, with finishing operations often overlooked. In this framework, the paper gives novel insights into the performance of AlSi9Cu3(Fe) fabricated through a process chain comprising PBF-LB/M, heat treatment, and final machining, showing the correlation of the alloy microstructural features and surface finish with the corrosion resistance. Besides the as-built (AB) condition, two different heat treatment conditions were proposed: direct ageing (T5), and solubilisation and ageing (T6). Microstructural analysis showed that, after T5, Si network remained intact, with minor Si precipitation. On the other hand, T6 fully homogenised the microstructure, dissolving the network and activating a massive precipitation of Si, Cu and Fe phases. Afterwards, turning tests were carried out at fixed cutting parameters, showing better surface results by increasing the treatment temperatures. Potentiodynamic polarisation tests on both machined and unmachined samples gave the corrosion potential and current density at varying initial microstructural conditions. The AB samples proved to have the highest corrosion resistance before and after machining, while the lowest was always offered by the T6 samples. An explanation of such behaviour was given based on a detailed microstructural analysis together with the evaluation of the surface quality.