Patent ID: 8430020

Claim:
A method for surface treatment of a skirt portion of a piston for an internal combustion engine, the method comprising: performing base treatment by injecting metal or ceramic fine particles having an average particle diameter of 20 μm to 400 μm with compressed air or compressed nitrogen as a mixture fluid onto the skirt portion of the piston for the internal combustion engine, made of an aluminum alloy, at an injection speed of 80 m/s or more or an injection pressure of 0.2 MPa or more to be collided with the skirt portion, thereby uniformly making a microstructure of a base material of the piston fine-grained in a depth range of 1 μm to 15 μm from a surface of the skirt portion and forming a modified layer with an activated surface; and forming a lubrication layer composed of a resin coating with a low friction coefficient on the surface of the skirt portion after the base treatment, while a newly generated face is exposed at a surface of the modified layer and is being activated.