On the selective corrosion mechanism of LPBF-produced AlSi10Mg: potentiostatic polarisation effects

Additive manufacturing technologies are quickly gaining success in several industries. However, a complete understating of how the unique macro- and microstructures obtainable influence the corrosion behavior is still far from being achieved. In this work, potentiodynamic and potentiostatic polarization tests were performed in an aerated chloride solution on laser powder bed fusion (LPBF)-produced AlSi10Mg specimens, built adopting different baseplate temperatures. Potentiodynamic polarization tests evidenced two separate breakdown potentials. The first was associated with the initiation of corrosion localized at the edge of the melt pool, while the second with the break of the passive film of the matrix. This phenomenon highlighted that potentiodynamic curves can overestimate the critical potentials required to trigger the selective corrosion. Potentiostatic polarization tests were performed at an intermediate potential value with respect to the ones highlighted in the previous test. All the specimens achieved the dissolution of the passive layer after a certain immersion time. This period was lower for the specimens built using higher baseplate temperatures, due to the coarsening of the microstructure and disruption of the Si-rich network. A similar behavior was encountered by the heat-treated samples. These required significantly less time to trigger corrosion, due to the complete disappearance of the melt pool macrostructure and formation of Si particles.