Normal temperature anodic oxidation of aluminum - dyed black - closed on the oxide film sporadic white spot is what is going on

It may be Al2O3 (alumina) aluminum exposed to air is easy to be oxidized, it is best to isolate the air, if not good operation, that is to use an external power cathodic protection law or sacrifice anode cathodic protection law. You just tie a piece of zinc to the aluminum

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