A double-layer chromium coating was prepared on a water pump shaft of engine by milky white chromium plating and bright chromium plating successively in the same bath and tank.The process flow is as follows:pretreatment,hanging,taking into tank,milky white corrosion-resistant chromium plating,bright wear-resistant chromium plating,taking out of tank,washing,hydrogen removal,polishing,and testing.The plating bath is composed of CrO3 200-250 g/L,H2SO4 2.2-2.6 g/L,and Cr3+2.0-3.5 g/L.The milky white chromium coating was obtained after plating at 60-65 ℃ and 15-25 A/dm2 initially for 30 min,and the milky white-bright double-layer chromium coating was then obtained after continuous plating at 55-60 ℃ and 40-50 A/dm2 for 90 min.The double-layer chromium coating has lower porosity as well as similar microhardness and wear resistance as compared with the single bright chromium coating.The practical production indicated that double-layer chromium coating has better corrosion resistance than single bright chromium coating.%以某型发动机的水泵轴为基体,在同一镀液和镀槽中电沉积制备乳白/光亮双层铬镀层.工艺流程为:前处理—装挂—入槽—镀乳白耐蚀铬—镀光亮耐磨铬—出槽—清洗—除氢—抛光—检验.镀液组成为:CrO3 200～250 g/L,H2SO4 2.2～2.6 g/L,Cr3+离子2.0～3.5 g/L.先在60 ～ 65℃、15 ～ 25 A/dm2下施镀30 min得到乳白铬镀层,随后在55～60℃、40～50 A/dm2下施镀90 min,即得乳白/光亮双层铬镀层.双层铬镀层的孔隙率比单层光亮铬镀层小,二者显微硬度相近,耐磨性优越.实际生产应用表明,双层铬镀层的耐蚀性优于单层光亮铬镀层.
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