This invention relates to a surface treatment method comprising the steps of soaking aluminum or an aluminum alloy in a treating solution containing a fluorine compound and ammonium silicofluoride, and treating the aluminum or aluminum alloy in the treating solution at a temperature in the range of 70 to 100.degree. C.; a piston having undergone such a surface treatment; and a piston coated with a film consisting of an Al-OH-F compound, as well as a sliding member in which its sliding surface and the like are coated with a slide film consisting, for example, of a compound of aluminum, fluorine and the hydroxyl group; and a surface-treating film for an aluminum alloy which is formed on a surface of aluminum or an aluminum alloy and consists of an aluminum fluoride hydroxide compound and silicon particles dispersed therein. The present invention can provide a surface treatment method which requires simple equipment, can reduce treating costs, and can yield aluminum or an aluminum alloy having excellent abrasion resistance, corrosion resistance and other properties, as well as sliding members and pistons having excellent abrasion resistance and other properties.

This invention relates to a surface treatment method comprising the steps of soaking aluminum or an aluminum alloy in a treating solution containing a fluorine compound and ammonium silicofluoride, and treating the aluminum or aluminum alloy in the treating solution at a temperature in the range of 70 to 100.degree. C.; a piston having undergone such a surface treatment; and a piston coated with a film consisting of an Al--OH--F compound, as well as a sliding member in which its sliding surface and the like are coated with a slide film consisting, for example, of a compound of aluminum, fluorine and the hydroxyl group; and a surface-treating film for an aluminum alloy which is formed on a surface of aluminum or an aluminum alloy and consists of an aluminum fluoride hydroxide compound and silicon particles dispersed therein. The present invention can provide a surface treatment method which requires simple equipment, can reduce treating costs, and can yield aluminum or an aluminum alloy having excellent abrasion resistance, corrosion resistance and other properties, as well as sliding members and pistons having excellent abrasion resistance and other properties.

Process for the alkaline passivation of galvanized and alloy-galvanized steel surfaces and of aluminum in strip lines, wherein the metal surfaces are brought into contact with an alkaline aqueous solution that contains complexing agents and iron, which has a free alkalinity in the range of 5 to 20 points and a total alkalinity in the range of 7 to 30 points and contains: 0.1 to 1 g/l magnesium ions, 0.1 to 1 g/l iron (III) ions and 0.5 to 5 g/l amino or hydroxy carboxylate ions. This may be followed by a chrome-containing or chrome-free secondary passivation.

In a method for the pretreatment of work pieces having a surface made of aluminium or aluminium alloys, for non-cutting shaping and/or the connection by welding or gluing to work pieces as well as for a subsequent permanent corrosion-preventing treatment, the work pieces are subjected to a three-stage treatment by a) rinsing with an aqueous, acidic solution containing a mineral acid, b) rinsing with water, c) bringing them into contact with an aqueous, acidic solution which is chromium-free and polymer-free and contains Ti and Zr as complex fluorides in a weight ratio of Ti:Zr of 2:1 to 1:2, in such a way that, after the subsequent drying off, a layer weight of 2 to 15 mg/m.sup.2 (calculated as Ti/Zr metal) results, wherein depending on the type of application, solutions having different concentrations and different pH values are used.

An amine fluoride neutralizing composition comprised of (a) about 1 to about 50 weight percent hydrofluoric acid, (b) optionally up to about 18 weight percent of a complex fluoride containing compound, and about 45 to about 99 weight percent of an amine. The weight percentages are based on the total solids of the amine fluoride neutralizing composition. Also provided is a method of using the amine fluoride to produce a non-chrome pretreatment composition comprised of mixing from about 20 to about 30 weight percent of the amine fluoride neutralizing composition with about 70 to about 80 weight percent of at least one organic resinous material having an organic resinous material that is amine neutralizable; and adding water so as to achieve a total solids content of the non-chrome pretreatment composition of about 20 to about 60 weight percent. The pretreatment composition may be further diluted with water to form a non-chrome pretreatment bath having a total solids content of about 0.1 to about 10 weight percent, preferably from about 1 to about 5 weight percent. The amine fluoride neutralizing composition allows for a simplified manufacturing process of non-chrome pretreatment compositions by allowing the use of one, less corrosive, easy to handle compound rather than three separate materials which may be hazardous to handle, and it allows for the insertion of fluoride into a pretreatment composition without the introduction of extraneous cations which can destabilize or diminish the effectiveness of the pretreatment concentrate or bath.