Aluminum part, e.g. a piston, is surface treated to form a sliding film

摘要

Aluminum and its alloys are surface treated by immersion in a solution containing a fluorine compound and ammonium hexafluorosilicate at 70-100 deg C. Independent claims are also included for the following: (i) a piston which has been surface treated as described above; (ii) a piston with a surface film of an Al-OH-F compound and/or an NH4MgAlF6 compound; (iii) a reciprocating part made of aluminum or an aluminum alloy coated with a surface sliding film consisting of one or more of a compound of aluminum, fluorine and a hydroxyl group, a hydrate of this compound and/or an NH4MgAlF6 compound, having a cubic crystalline structure with no crystal orientation; (iv) a reciprocating part made of aluminum or an aluminum alloy coated with a 1-100 mu m thick surface sliding film consisting of 1-100 mu m size aggregates, each of which is formed of <= 1 mu m size micro-crystals; and (v) an aluminum surface treatment film consisting of an aluminum fluoride-hydroxide compound and/or an NH4MgAlF6 compound containing 1-24 wt.% dispersed silicon particles, the silicon content of the aluminum alloy being 4-24 wt.%.