the structure of aluminum castings is loose, high porosity, and contains a variety of metal and non-metallic impurities, and the quality of anodic oxide film is difficult to guarantee. In order to obtain normal oxide film quality and avoid white spots after anodizing film dyeing, the following measures can be taken.

  (1) high voltage and large current density impact method. In the initial stage of anodization, high voltage and high current impact were used to separate the size of &ldquo, &rdquo, which was originally separated by impurities, and connected to the chip through large current impact. The specific process is as follows: the initial voltage of anodizing is about 30V, the current density is about 2 ~ 2.5A/dm2, and the anode oxidation voltage is returned to normal after 3 to 5min. The anode oxidation is 50min, then the more satisfactory oxide film can be dyed, and the white spot base is disappearing. The above method is inadequacies in that if the casting has a screw hole, it may be slightly enlarged. Therefore, it is necessary to control the large current density, the anodic oxidation time of high voltage and prevent the temperature of the anodized solution from increasing too quickly. During continuous production, cooling measures should be adopted in anodizing solution.

  (2) the grinding method of the surface of the casting. Grinding can make the worn aluminum end fill the pores of the casting, and play a bridge role connecting the block &ldquo which is segregated by impurities; island &rdquo. The actual effect of this method is slightly less than the method (1), because the aluminum end of the grinding can not play a real filling, bridge effect, and some parts of the filling will be corroded in the process of alkaline and anodic oxidation.

  (3) shot peening on the surface of the castings. Before the shot peening method, the author uses the method of hammering with a round head, the original intention is to make the barrier “ the gap of the island &rdquo is closed by knocking and closing, and the result is remarkable. It is considered that the efficiency of shot peening will be greatly improved, and the effect of anodizing and dyeing is better than the above two methods.

  and   the wall thickness of the general cast aluminum can meet the pressure requirement of the shot peening. It is favorable to improve the quality requirements of the shot peening by the larger pressure, and the effect of the closed pores and crevice through the extrusion of pellets, and the strength and neatness of the surface of the cast aluminum parts can be improved.

    it was mentioned why there was no white spot after anodic oxidation on the surface of unprocessed castings, because the surface of the castings had a dense oxide film.