Abstract: A piston formed from an Al—Si alloy having an average Si composition includes a high wear region having a surface that is Si-rich with respect to the average Si composition of the Al—Si alloy. The surface of the predetermined high wear region is treated, as by etching, to selectively remove Al from the surface to produce the Si-rich region. The Si-rich region has improved resistance to wear. The piston may be treated to produce one or more high wear regions which are Si-rich with respect to the average Si composition of the alloy. High wear regions may include the annular grooves for receiving a piston ring, the piston skirt and the pin bore.

Abstract: A piston formed from an Al alloy, such as an Al—Si alloy, has wear resistant coating applied to a predetermined portion of the outer surface. The predetermined portion of the outer surface preferably includes the piston skirt. The coating includes an adhesion promoting primer layer of a silane and a polymer coating layer. The silane primer coating promotes adhesion between the Al-alloy and the polymer coating.