热扩散处理对热浸镀铝Fe−Cr−Si−B铸钢组织演变及腐蚀行为的影响

Influence of thermal diffusion treatment on microstructure evolution and corrosion behavior of hot-dipped Al coated Fe−Cr−Si−B cast steel

研究热扩散处理对热浸镀铝Fe−Cr−Si−B铸钢镀层组织及在5%(质量分数)NaCl溶液中的腐蚀行为的影响。结果表明:Fe−Cr−Si−B铸钢中的Fe基体与Al液界面反应产物为柱状结构的FeAl3。在(Cr,Fe)2B/Al界面上形成的周期性层片结构是在热扩散处理过程中形成,而非热浸镀铝。在短时间内表面残留Al层主导了热浸镀铝和热扩散处理镀层在NaCl溶液中的腐蚀行为,直到表面残留Al层被完全消耗。Cl−引起的点蚀优先从块状B−Al−Cr相与FeAl3的界面开始,并沿周期性层片结构扩展。硅颗粒作为阴极,促进了镀层的腐蚀。在Fe−Al金属间化合物层被完全腐蚀之前,钢基体都处于阴极保护中。此外,高温NaCl溶液的腐蚀被显著加速。

The influence of thermal diffusion treatment on the microstructure and corrosion behavior of hot-dipped Al coated Fe−Cr−Si−B cast steel in a 5 wt.%NaCl solution was studied.The results showed that the product obtained from the interfacial reaction between the Fe matrix in Fe−Cr−Si−B cast steel and molten Al was FeAl3 with a columnar crystal structure.Periodic layered structures at the(Cr,Fe)2B/Al interface were formed during the subsequent thermal diffusion treatment but not hot dip aluminizing.The corrosion behavior of the residual Al layer predominated that of the hot dip aluminizing and thermal diffusion treatment coatings over a short duration till the Al topcoat was consumed completely.Localized corrosion caused by Cl−preferentially began from the block-like B−Al−Cr phase/FeAl3 interface and propagated along periodic layered structures.The Si particles acted as a cathode and promoted the corrosion of the coating.The steel substrate retained its cathodic protection until the Fe−Al intermetallic compounds layer was corroded completely.Additionally,the corrosion in the NaCl solution at an elevated temperature was greatly accelerated.