Effect of Si network continuity on the localized corrosion of AlSi10Mg alloy fabricated by selective laser melting

Abstract

This paper aims to investigate the influence mechanism of silicon (Si) network morphology on the localized corrosion behavior of AlSi10Mg alloy prepared by selective laser melting (SLM) in 3.5 wt% NaCl solution. Four different Si microstructures, i.e., coarse Si network, fine Si network, broken Si network, and isolated Si particles, were regulated through stress relief annealing at 200 °C and 300 °C (designated as SR200 and SR300 respectively), and T6 heat treatment. Microstructure observation, electrochemical testing, corrosion morphology characterization, and scanning Kelvin probe force microscopy (SKPFM) are used to identify the corrosion mechanism. The results show that heat treatment significantly changes the morphology of Si microstructure. The SLM-AlSi10Mg alloy mainly undergoes pitting corrosion in NaCl solution, and pitting preferentially occurs at the molt pool boundary (MPB). The oxide film on the alloy surface has a bilayer structure: inner dense Al₂O₃ layer and outer porous Al(OH)₃ layer. A more uniform and dense oxide film with stronger protectiveness is formed on Al matrix with networked Si. The inner dense layer on Al matrix with the particulate Si is thinner than with the Si network, resulting in weakened protectiveness. SKPFM analysis reveals that the potential difference between Si and Al matrix increases with the coarsening of the Si network, and the MPB becomes a preferential corrosion area due to the larger potential difference. This study provides a theoretical basis for optimizing the corrosion resistance of SLM-AlSi10Mg alloy.