In situ investigation of sacrificial behaviour of hot dipped AlSi coating in sulphate and chloride solutions

The electrochemical behaviour of the cut-edge of hot-dipped aluminium–silicon-based alloy coated steel is studied in immersed conditions in sulphate and in chloride media. Preliminary studies performed on steel-pure Al bi-electrode demonstrate that a significant galvanic current can develop at short times (t < 1000 s) only in chloride solutions. In situ measurements of current density and pH distributions over cut-edge coated steels immersed in chloride solutions revealed a quasi-steady state current between the coating and the steel substrate, resulting from local (pitting like) dissolution of the aluminium–silicon-based alloy coating. In sulphate solutions, the coating is not at all sacrificial and remains passive.

► The sacrificial behaviour of a HDG Al–Si coating is studied on steel sheets.
► The electrochemical behaviour of Al and Al–Si coatings are compared.
► Pure Al is sacrificial only at short times (t < 103 s) and in chloride solutions.
► HDG Al–Si coatings are sacrificial only in chloride solutions.