Zn-Co-Cr-Al_2O_3 分散めっきの皮膜構造と複合サイクル試験による変化

概要

論文の詳細を見る
The microstructure and chemical state of Zn-Co-Cr-Al_2O_3 composite coating before and after the cyclic corrosion test (CCT) were investigated by electron microscope, X-ray photoelectron spectrometer, and electron probe micro analyzer. The coating layer consisted of a Zn matrix containing super-saturated Co and dispersed particles of cohesive Al_2O_3, Cr_2O_3, Cr(OH)_3 coordinating SO_4. The dispersed particles existed uniformly in a regular matrix in coatings formed in electrolytes with lower concentrations of dispersed Al_2O_3 particles and Cr-ions, while the matrix was dendritic and the dispersed particles concentrated along the dendrite arms in coatings formed in electrolytes with higher concentrations of Al_2O_3 particles and Cr-ions. The main corrosion products of the composite coating after the CCT were ZnCl_2・4Zn(OH)_2 and ZnO, which is similar to that with conventional Zn coatings, but the amount of the Zn rust is less than that with conventional Zn coatings. Fine networks of ZnCl_2・4Zn(OH)_2 grew in the coating in the vicinity of the steel substrate during the CCT. A region of highly-condensed dispersed particles existed between the ZnO layer and the residual coating layer. It is considered that ZnCl_2・4Zn(OH)_2 formed uniformly by the local cathodic reaction of Co, and the existence of the protective region of dispersed particles gave high corrosion resistance to the composite coating.
社団法人日本鉄鋼協会の論文
1996-01-01