Reconditioning of Electroless Nickel Plating Bath on Magnesium Alloys
The reconditioning operation of electroless nickel (EN) plating was studied and the influence of aging on the deposition speed, phosphorous content and stability of the operating solution was analyzed. The results showed that aging of the EN bath caused a dramatic declining of the deposition speed and the bath stability, while a slow increasing in phosphorous content of the deposit. Fluoride of NaF and NiF2 would precipitate from the bath due to the accumulation of sodium and fluorine ions during the replenishment. The sediment of NaF and NiF2 had a detrimental effect on the EN process and would deteriorate the protection of EN plating. The electroless nickel (EN) plating has been used in the industries on a large scale. Since the operational life of EN bath is referred to the cost of the EN process and environmental pollution of the disused plating bath, it now has been emphasized in the world 1-3. Nickel is replenished as a dissolved salt, traditionally nickel sulphate. In this way, sulphate and breakdown products of the chemical reducer build up in the process solution over time. Unless specific techniques used to remove these substances, bath life will be limited to 4 to 10 metal turnovers (MTO). With typical high-phosphorus applications, 4 MTO is the maximum bath life. The need to extend the operational life of EN solutions, or even to operate these endlessly, is probably as old as the technology itself. Different from the commonly used EN process on steel and aluminum alloys, the EN process on magnesium alloys has a unique formula 4-7. It was found that nickel chloride and nickel sulphate may not be used as the source of nickel ions in the EN bath for magnesium alloys. While basic nickel carbonate or nickel hydroxide is usually employed to obtain the nickel ion concentration. Since such nickel sources dissolve little in pure water, hydrofluoric acid, which is compatible with the components of the plating bath, is usually used to dissolve nickel carbonate or nickel hydroxide. It surely causes the increase of fluorion concentration in the plating bath gradually using this method to make up the consumption; and the replenishment of sodium hypophosphite causes the increase of concentration of sodium ion in the plating bath gradually too. Whereas, the solubility for fluorides of Ni2+ and Na+ is limited, it will generate sediment in the course of the EN plating process. What is the influences of the sediment on the deposition of nickel, and how to extend the operational life of EN solutions; all these issues need to be studied. However, the information published openly of the research on the aging of the EN bath for magnesium alloys can hardly be read. To explore the technology for reconditioning of the EN bath on magnesium alloys, the effects of aging of the EN bath was systematically studied in this paper.
magnesium alloys electroless nickel plating stability
LIU Xinkuan LIU Ping XIANG Yanghui HU Wenbin DING Wenjiang
School of Materials Science and Engineering, University of Shanghai for Science & Technology,Shangha National Engineering Center of Light Weight Alloy Net Forming, Shanghai Jiaotong University, Shangha
国际会议
11th IUMRS International Conference in Asia(第十一届国际材联亚洲材料大会 IUMRS-ICA 2010)
青岛
英文
720-726
2010-09-25（万方平台首次上网日期，不代表论文的发表时间）