Whether the metal cleaning agent sold in the city can be applied to the cleaning of aluminum parts, it is necessary to first know the pH value range. If the pH value is too high, it cannot be used. Otherwise, the surface of the aluminum parts may be subject to corrosion. Because these metal cleaners are usually free of aluminum corrosion inhibitor components, they do not act to prevent the etching reaction, so that when the oil stain on the metal surface is washed off faster, it also causes the surface of the aluminum parts to be spotted. In order to avoid the occurrence of the above phenomenon, first of all, we must fully pre-treat, that is, before the full degreasing with organic solvents, so that the surface reaches a substantially uniform degree of cleanliness, before using this metal cleaning agent.