提出了一种两步法退除镁合金基体上不合格化学镀镍层的工艺，即先利用F?保护基体，在酸性体系中作预退除，再利用 OH?保护基体，在碱性体系中作深度退除。通过正交试验得出了预退除步骤的最优配方为：氢氟酸400 g/L，浓硝酸50~500 g/L，十二烷基硫酸钠0.05 g/L，氯化钠0.05 g/L，柠檬酸钠30 g/L，尿素20 g/L，特殊缓蚀剂5 g/L。总结了预退除工序的关键因素──退除时间──与硝酸浓度及退镀量之间关系的经验公式，可通过控制工艺来防止镁基过腐蚀。结果表明：该工艺不腐蚀基体，成本低廉，退除速度较快，成功实现了带凹槽的AZ91D镁合金件的返修，重新施镀后镍镀层的结合力和抗腐蚀性能均良好。
A two-step process for stripping unqualified electrolessly plated nickel coating on magnesium alloy substrate was developed: (1) pre-stripping in an acidic electrolyte using F? to protect the substrate; and (2) deep stripping in an alkaline electrolyte using OH?to protect the substrate. The optimal bath formulation of pre-stripping procedure was obtained by orthogonal test as follows: HF 400 g/L, concentrated HNO3 50-500 g/L, sodium dodecyl sulfate 0.05 g/L, NaCl 0.05 g/L, sodium citrate 30 g/L, urea 20 g/L, and specialty inhibitor 5 g/L. An empirical equation for processing time, a key variable in pre-stripping procedure as a function of HNO3 concentration and coating thickness, was summarized to control the process and prevent the excessive corrosion of substrate. The results showed that the process has advantages of no corrosion of substrate, low cost, and fast stripping rate. The repairing of an AZ91D Mg alloy part with grooves was achieved. The nickel coating re-plated has good adhesion strength and corrosion resistance.
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