The differences of surface morphologies of tin-free steels obtained with different current density distribution schemes were studied by scanning electron microscopy. The results showed that there exist many pores on rough surface of the tin-free steel obtained by increasing the current density gradually. The tin-free steel obtained by applying a constant current density has a fine surface with many pores. The surface porosity and morphology of tin-free steel were evidently improved by decreasing the current density gradually. The surface of the chromium coating obtained by applying low and high current density alternately is uniform, smooth, and less porous. The analysis of polarization curves in 3.5wt% NaCl solution and neutral salt spray (NSS) test showed that the tin-free steel obtained by alternating current density has better corrosion resistance than those obtained with other current density distribution schemes. The equations presenting the relationship between NSS test temperature and time of the first rust spot appearance were established for the tin-free steels obtained with different current density distribution schemes.%采用扫描电镜分析了不同电流密度分配制度下所得无锡钢板表面形貌的差异.结果表明,电流密度逐渐增大的分配制度获取的无锡钢表面存在较多孔隙,且镀层表面粗糙.电流密度平均分配时获取的无锡钢表面尽管同样存在较多孔隙,但是镀层表面较为细腻.电流密度逐渐减小的分配制度获取的无锡钢表面孔隙率和状态均明显改善.电流密度交叉式分配制度获取的无锡钢表面孔隙率少,且铬镀层均匀、细腻.根据3.5％(质量分数)NaCl溶液中的极化曲线和中性盐雾试验分析可知,与其他电流密度分配制度相比,交叉式电流密度分配制度获取的无锡钢耐蚀性较好.建立了不同电流密度分配制度下所得无锡钢在中性盐雾试验中的点蚀产生时间与试验温度的方程.
展开▼
