Anodizing of Aluminum

When anodizing, the aluminum is hung in an acid bath and connected as the positive pole. This forms a hard, porous oxide layer on the surface that can later be dyed or sealed. But this layer is a good insulator, meaning: for welding you have to grind it off completely in the weld area, otherwise you won't get a clean weld and the material will only contaminate the bath. The oxide layer is also much harder than the base material, so use a sharp tool and remove it generously. If you don't remove the layer, it burns off during welding and leaves pores and inclusions.