In order to be suitable for die casting, people add a lot of silicon to the aluminum alloy used for die casting. When the aluminum alloy condenses in the mold, the silicon will float on the surface to form a layer of silicon film that is very hard and wear-resistant. Some OEM designers use this feature to directly design the inner surface of the die casting hole as a bearing surface. This silicon surface layer is generally only 0.2 to 0.9 mm thick. With too much processing, the life of the bearing surface will be shortened.