The concentration of zinc on the surface of brass plating is higher than that of the average composition of the brass.
Better retention of adhesion after humidity aging is achieved at a higher zinc content of brass, having the positive effect of ZnO at brass surface.
ZnO at the surface inhibits the formation of excessive and loose bonding products during humidity aging. Compounds which promote the formation of ZnO at the interface during bonding maintain the high adhesion level.
A small amount of cure accelerator or the use of a low accelerator to sulfur ratio makes the ZnO at the interface.
But the level of ZnO also increases with time of humidity aging. It seems that the ZnO of this type forms a poor bonding layer during dezincification after humidity aging.