Corrosion behavior and mechanism of electric arc-sprayed Al-Mg coating and Zn-Al-Mg pseudo-alloy coatings

Abstract

Pseudo-alloy coatings produced using the electric arc spray method are economical for corrosion protection in large-scale applications. In this study, the corrosion behaviour of two Zn-Al-Mg pseudo-alloy coatings (Al-5%Mg wire + Al-50%Zn wire and Al-5%Mg wire + 99.9%Zn wire) is investigated. A reference coating (Al-5%Mg) is also tested for comparison. The results show that the variation in the Zn content significantly affects the corrosion mechanism, including corrosion kinetics, corrosion development pathway, and corrosion products. Selective dissolution is inevitable in the pseudo-alloy coatings due to the phase segregation caused by multi-galvanic systems. Severe corrosion reactions can occur if these galvanic cells are confined in a limited space, such as in a single colony. If the electrodes of these galvanic cells are relatively large, the dissolution process can be slow but continuous. Both Zn-Al-Mg pseudo-alloy coatings exhibit improved corrosion resistance due to the barrier effect of the AlMg splats and can provide adequate sacrificial protection owing to the more negative corrosion potential of the Zn-rich splats.