The microstructure and electrochemical performance of the Al-10Si-3.5Fe-xZn-yGa alloys for hot-dip galvanizing in low-chloride environments

Abstract

The microstructure and electrochemical performance of Al-10Si-3.5Fe-xZn-yGa alloys in low-chlorine environments were studied by SEM observation and electrochemical analysis. The microstructure of Al-10Si-3.5Fe-xZn-yGa alloys consisted of Si phase, τ6, and α-Al matrix. The addition of Zn or Ga did not affect the morphology and phase of the microstructure. Pitting corrosion, galvanic corrosion of α-Al matrix with Si phase and τ6, and anisotropic corrosion of τ6 occur in the low-chloride environments for the alloys. The addition of Zn not only promoted the development of pitting pits on the α-Al matrix but also reduced the electrode potential of the α-Al matrix, increased the galvanic corrosion potential difference, and accelerated the corrosion rate of the α-Al matrix. The addition of Ga could induce pitting corrosion on the surface of intact τ6 and α-Al matrix synchronously, reducing both electrode potential and accelerating the alloy's corrosion rate. The synergistic action of Zn and Ga could promote the alloy's sustained activation. Corroded τ6 developed cracks and fragmentation, with the resulting cracks serving as pathways for the ingress and egress of Cl− and other particles, leading to internal corrosion of the alloy. The stress generated during the fragmentation process of τ6 promoted extensive delamination of the alloy surface, preventing corrosion products from covering the alloy's surface.