If there is white spot on the surface of aluminum alloy die casts
after anodizing, what's the reason? If this kind of problem occurs, it is probably because its structure is too loose. Which makes the material porosity too high. Further more, too much impurities in the raw materials would also cause white spot. So we need to take some necessary measures to solve and prevent the situation:
: High voltage and large current density impact method. We can adopt high voltage and high current in the early stage of anodic oxidation, so that the "island" which was divided by impurities could be connected to one piece through high current impact. And then we could wash and dye a satisfactory oxide film and white spots basically disappeared.
Shortcomings of methods above is that if the cast has screw hole, it may be slightly expanded. it is necessary to control the high current density, anodizing time of high voltage, and prevent temperature of anodic oxidation solution from rising too fast. We need to take measures to cool continue to manufacture the anodized solution if the manufacturing continues.
: Casts surface grinding method. Abrasive can make the grinding aluminum fill castings pores, which play a role in connecting the island that was isolated by impurities.
Sometimes the grind aluminum could not really fill the pore, the filler would fall off because of corrosion in the alkaline etching and anodic oxidation process.
: casting surface shot peening method. If you use a round hammer to knock the cast so as to close the pore which blocks the island and achieve one piece. That is very effective.