Aluminum alloy piston and piston-ring assembly treated to suppress agglutination of the piston alloy to a piston-ring

A piston and piston-ring assembly for an internal combustion engine, comprising:

• a piston comprising aluminum base alloy, the piston being formed with piston-ring grooves, each of the piston-ring grooves being defined by a groove surface including a groove upper surface, a groove lower surface and a groove side surface connecting the groove upper and lower surfaces when the piston is vertically orientated, such a kind of surface hardening treatment as is accompanied by an increase in surface roughness being applied to at least a groove lower surface of at least a top piston-ring groove;
• and
• piston-rings located in the piston-ring grooves, each of the piston-rings including a ring upper surface, a ring lower surface ad a radially inside ring side surface opposing the groove upper surface, the groove lower surface, and the groove side surface of a corresponding piston-ring groove, respectively, when the piston is vertically orientated, at least a surface of a piston ring opposing the hardened surface of the piston-ring groove being formed with a coating layer including resin with an excellent adhesive property as a base material of the coating layer.