Influence of additional Mg on intergranular corrosion susceptibility of brazed Al-Mn-Si-Cu alloys and improvement effect by Ti

Abstract

The present study investigated the influence of additional Mg on the intergranular corrosion (IGC) susceptibility of brazed Al-Mn-Si-Cu alloys. IGC did not occur in the water quenched samples, whereas samples treated with slow cooling rate showed high IGC susceptibility. As a result of anodic polarization measurement, non IGC susceptibility samples showed a single pitting potential, but high IGC susceptibility samples showed double pitting potentials. On slowly cooled Al-Mn-Si-Cu-Mg alloys, the precipitation of Al₁₅ (Mn, Fe)₃Si₂ were observed in the grain interiors and on the boundaries, but Q-phase on the grain boundaries. Precipitated Q-phase induced forming Si/Cu/Mg-depleted zone near the grain boundaries. This zone, of which pitting potential is less noble than the grain, dissolved preferentially, hence IGC susceptibility increased. Furthermore, we clarified additional Ti improved the IGC susceptibility of Al-Mn-Si-Cu-Mg alloys. It was considered that potential gap due to Ti layered distribution prevented intergranular corrosion progress.