Because zinc is an amphoteric metal, it is both soluble in acid and soluble in alkali. The proportion of zinc in zinc aluminum alloy aluminum die castings accounts for more than 90%. (Aluminum content is about 4%) Therefore, it is reasonable to consider etching by zinc. Because the surface of the zinc-aluminum die-casting compact layer is very thin (only 0.O5 ~ O.1mm), it should be very careful when etching. General etching selection l%. The 2% hydrofluoric acid aqueous solution or the 1% to 2% sulfuric acid aqueous solution is etched at room temperature for 5-30 seconds and then transferred to the next activation step.