Corrosion of Al-3.5Cu-1.5 Mg–1Si alloy prepared by selective laser melting and heat treatment

Abstract

The corrosion properties of selective laser melted (SLM) and of additionally heat-treated (T6) Al-3.5Cu-1.5 Mg–1Si samples were assessed in 0.001 M and 0.1 M NaCl solutions (pH 7) by means of electrochemical polarization measurements and SEM surface analysis. In both solutions these new alloy types exhibited improved corrosion behavior compared to wrought and heat-treated AA 2024 reference states. This is attributable to more refined microstructural states and to the formation of particular phases. The SLM samples comprise finely dispersed Q-phase particles which act cathodic and thus, trigger adjacent matrix phase dissolution. Additional T6 heat treatment was efficient for attaining the lowest corrosion current density of ~0.04 μA/cm2 and a widening of the anodic passive range to ~400 mV in 0.1 M NaCl. Only this alloy state shows a repassivation ability upon reverse scanning. T6 treatment yields mainly the Mg2Si phase acting as local anode and a widely passive Al-based matrix phase. Altogether, SLM processing with final heat treatment of the Al-3.5Cu-1.5 Mg–1Si alloy is suitable for achieving not only superior mechanical performance but also improved corrosion stability.