Co-Mo alloy plating from ammonium-citrate bath was studied for the purpose of developing a new pretreatment method for direct-on enameling on steel sheet.
The effect of plating conditions on the Co/Mo alloy ratio was studied first, and on the basis of the results, the effect of the Co/Mo ratio on adhesion for direct-on enameling was examined.
It was found that: 1) Co/Mo alloy ratio in the electrodeposit was affected by bath composition including the concentration ratio of CoSO₄ to Na-citrate, the ammonium hydroxide concentration and pH. 2) To obtain excellent adhesion for direct-on enameling, Co-Mo alloy deposits on steel sheet should have Co/Mo ratio of less than 1.4:1 and coating weight of more than 1.5g/m² for both Co and Mo.