The main purpose of the research was to develop an electroless nickel bath with long cycles and high stability. Thiourea and potassium iodate were added in the electroless bath as the stabilizing agents. The effects of temperature and pH values on the bath stability

plating rate and coating quality were studied. Weighing was used to measure the deposition rate of coating. The stability of the bath was characterized by percentage of the nickel on the surface of work piece to total nickel consumption in the bath. The coverage of coating was evaluated by immersion test in NaCl solution. The adhesion of coating was evaluated by thermal shock test. Polarization curves were used to characterize the corrosion resistance of coating. The results showed that the deposition rate increased at first

then went down with increasing concentration of thiourea or potassium iodate. The deposition rate was more significantly affected by thiourea than that by potassium iodate. The maximum value of stability constant reached 89.25% in the bath of 0.5 mg·dm-3 thiourea and the stability constant was 82.45% in the bath of 5 mg·dm-3 potassium iodate. When plating was carried out at （82±1）℃ in the pH5. 0 bath of 0.5 mg·dm-3 thiourea

uniform and dense coating was obtained

and there was no gap between Ni-P coating and Mg substrate. Thiourea not only improved the deposition rate

but also catalyzed the surface of magnesium alloy and raised the deposition efficiency.