Studies of the Blisters on the Plated Surface of Zinc Alloy Die Castings

Studies were made on the blisters which appear on the plated surface of zinc alloy die castings after several months more since the plating. The processes for accelerating the appearance of these blisters were also discussed. The following results were obtained(1) Each blister had a circular gap of 30-40μ in dia. at its centre, from which cracks radiated.(2) Growth of blisters was due to the corrosion of the substratum of zinc alloy.(3) For accelerating the appearance of blisters, it was found to be most effective to immerse the castings in the solution of about 3% of NH4Cl in boiling.(4) The blisters appeared in the above test were considered to be the same in nature as that in practice. Accordingly, the above test would be most available for detecting the surface defects for blistering source.