Effect of Cu content and quenching rate on the intergranular corrosion behavior of Al-Zn-Mg-Cu alloys

The effect of Cu content and quenching rate on the intergranular corrosion behavior of Al-Zn-Mg-Cu alloys has been investigated. The study reveals that at the same quenching rate, the intergranular corrosion susceptibility increases with the elevation of Cu content. Meanwhile, for alloys containing the same Cu content, the intergranular corrosion susceptibility increases as the quenching rate decreases. Remarkably, at high quenching rates, primarily pitting corrosion occurs. However, once the quenching rate falls below a specific threshold, the corrosion tends to propagate along grain boundaries. The critical quenching rate required for this transition increases with the increase of Cu content. Both the corrosion initiation and propagation are related to the Volta potential difference between grain boundary precipitates and the matrix (VPDG), which escalates correspondingly with the elevation of Cu content or the reduction of quenching rate. The intergranular corrosion behavior has been discussed through a comprehensive analysis encompassing VPDG, the features of grain boundary precipitates and precipitate-free zones. [Display omitted]