A study of chromium-free pickling process before electroless Ni-P plating on magnesium alloys

► A chromium-free pickling process is developed for Mg alloys. ► Pickling mechanism of Na2MoO4 + H3PO4 solution is described. ► Electrochemical behaviors of pickling and activation are explained. ► Highly qualitative Ni-P coating is obtained through the new pretreatment.