| 摘要 |
PROBLEM TO BE SOLVED: To facilitate the equipment, to reduce the treating cost and to impart excellent wear resistance, corrosion resistance or the like by heating a treating soln. contg. ammonium borofluoride or ammonium chloride or ammonia water and magnesium silicofluoride to a specified temp. and dipping Al or an Al alloy therein. SOLUTION: This surface treating method is the one in which a treating soln. is heated at 70 to 100 deg.C. Preferably, the treating soln. contains magnesium silicofluoride of 0.1 to 20 pts.wt. to 100 pts.wt. of water and an ammonium compd. or ammonia water by 0.01 to 10 pts.wt. by the amt. of ammonium, moreover, the surface of a piston is coated with a film composed of a mixture of NH4MgAlF6 and MgAlF5.1.5H2O or a mixture of NH4MgAlF6 and MgAl2F8.2 H2O, and furthermore, the piston is the one in which the whole face including the inner and outer faces of the piston is coated with a film composed of a similar mixture, and the thickness of the film of the similar mixture lies in the range of 1 to 20μm.
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