During the casting process, the aluminum casing is prone to internal looseness, shrinkage, porosity, and the like. After the machining of the defective casting, the surface dense layer component is removed to expose the internal tissue defects. For automotive aluminum housings with sealing requirements, such as cylinder block, cylinder head, intake manifold, brake valve body, etc., when the pressure sealing test is carried out, the presence of defective micropores will cause leakage of the sealing medium to cause a large amount of waste. And these defects are often found after being machined by pressure testing, resulting in serious waves of working hours, raw materials and energy.

In order to solve the problem of high scrap rate of aluminum casing of automobile, and to save the aluminum casing which may be scrapped due to the above defects, certain treatment measures must be taken in production, and the common technology currently used is infiltration treatment, that is, plugging. The so-called "impregnation" means that the infiltrant is infiltrated into the micropores of the aluminum casing under certain conditions. After solidification, the filler penetrating into the pores is integrated with the inner wall of the pores of the casting to block the micropores, so that the parts can be satisfied. Process technology for conditions such as pressurization, seepage prevention and leakage prevention. The surface of the aluminum casing is rich and varied, and polishing is only one of them, but it is an important process to improve the quality of the aluminum casing. Mastering a reasonable polishing method can improve the quality and performance of the aluminum casing, thereby improving the quality of the aluminum alloy die-casting product.

In addition to conventional mechanical polishing and chemical polishing, there are electropolishing, ultrasonic polishing, fluid polishing, magnetic polishing, and medium-electric spark ultrasonic composite polishing. The basic principle of electrolytic polishing of aluminum casing is the same as that of chemical polishing, mainly relying on selectively dissolving tiny protruding portions on the surface of the material to make the surface smooth. Compared with chemical polishing, it can eliminate the influence of the cathode reaction and has a good effect.

The ultrasonic polishing of the aluminum casing is a processing method of polishing the brittle hard material by the abrasive suspension by using the tool section as the ultrasonic vibration. The workpiece is placed in an abrasive suspension and placed together in an ultrasonic field, and the abrasive is ground and polished on the surface of the workpiece by the action of ultrasonic waves.

The fluid-polishing technique of the aluminum casing relies on the flowing liquid and the abrasive particles it carries to flush the surface of the workpiece for polishing purposes. Hydrodynamic grinding is driven by hydraulics. The medium is mainly made of a special compound that flows at a lower pressure and is incorporated into an abrasive. The abrasive can be made of silicon carbide powder.

Magnetic polishing is also one of the polishing techniques involved in the processing of aluminum casings. Magnetic abrasives are used to form abrasive brushes under the action of magnetic fields to grind workpieces. This method has high processing efficiency, good quality and easy control of processing conditions. With a suitable abrasive, the surface roughness of the machine can be achieved up to 0.1 μm.