Distinction of corrosion resistance of selective laser melted Al-12Si alloy on different planes

Electrochemical measurements and microstructural studies were carried out to investigate the corrosion behaviour of the different planes for the Al-12Si alloy produced by selective laser melting (SLM). The electrochemical results demonstrate that the building direction plane (XZ-plane) of the SLM-produced alloy exhibits better corrosion resistance in comparison with the building plane (XY-plane) in 3.5 wt% NaCl solution. The relatively inferior corrosion resistance of the XY-plane is ascribed to that the grown corrosion products extrude the deep and small-bore Si shells on the aluminum substrate, thereby causing the crack of Si shells. Without such a cover of the Si shells, the Cl− would continuously penetrate into the aluminum substrate and ultimately induce occurrence of the severe pitting. As for the XZ-plane, the corrosion products cannot grow and deposit in its shallow and large-bore Si shells, instead of transferring to the testing solution. The undamaged Si shells and formed oxide film constitute a protective layer to protect the aluminum substrate from the attack of Cl−, thereby displaying superior corrosion behaviour for the XZ-plane.