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Plating method for aluminum alloy materialRelated Patent Categories: Electrolysis: Processes, Compositions Used Therein, And Methods Of Preparing The Compositions, Electrolytic Coating (process, Composition And Method Of Preparing Composition), Treating Substrate Prior To Coating, Treating Substrate With Liquid Other Than Tap Water (e.g., For Removing Foreign Material, Etching, Activating, Etc.), Predominantly Aluminum SubstratePlating method for aluminum alloy material description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060226020, Plating method for aluminum alloy material. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present invention relates to a method for applying hardwearing plating to an aluminum alloy material. In particular, the present invention relates to a plating method for an aluminum alloy material, which makes it possible to minimize environmental load in the pretreatment for plating. [0002] There are existing methods for applying hardwearing plating, iron plating, to an aluminum alloy material such as a cylinder for an internal combustion engine (the sliding surface of piston) such as a Schnurle scavenging type small air-cooled two-stroke gasoline engine. It has been the conventional practice, as described in JP Patent Laid-open Publication (Kokai) No. 3-191095 (1991), to perform a pretreatment (substrate treatment) in order to enhance the adhesion (biting properties) of plating to the surface of aluminum alloy material prior to the plating process. [0003] This pretreatment has been conducted in a sequence of processes (steps) and under the treatment conditions as shown in the following Table 1. Specifically, the aluminum alloy material is subjected to a degreasing treatment, and the material thus degreased is washed with water and subjected to alkaline etching. The material thus alkali-etched is washed with water and then treated with a mixed solution composed of nitric acid, hydrofluoric acid and sulfuric acid to dissolve and remove (pickling) insoluble matters (smut: Si, Cu, Fe, Mn, etc.) in the material (aluminum alloy) generated (left remaining on the surface layer) in the previous alkaline-etching step. As a result, the surface of the material is made clean, concurrently creating fine recessed and projected portions on the surface of the material. Thereafter, the resultant surface is washed with water and then subjected to an anodic oxidation treatment. As a result, an oxide film is created on the surface of the material and, at the same time, holes are created at portions corresponding to the fine recessed and projected portions of the oxide film. The material having the fine recessed and projected portions formed thereon is washed with water and then the surface of material is subjected to iron plating. In this case, since the iron plating (lowermost portions thereof) is permitted to penetrate into the surface of material so as to bury the holes and the fine recessed and projected portions, it is possible to obtain high anchoring effects, thus rendering the plating excellent in adhesion (biting properties). TABLE-US-00001 TABLE 1 (Conventional method) Steps Conditions of treatments Degreasing Bondal Cleaner (Canning Co.): 2.5 g/L, 50.degree. C., 45-55 seconds Water washing Alkali etching Bondal Cleaner (Canning Co.): 25 g/L, 60.degree. C., 45-55 seconds Water washing Pickling Sulfuric acid: 53%; nitric acid: 11%; hydrofluoric acid: 10%; 20-30.degree. C., 45-55 seconds Water washing Anodic oxidation Phosphoric acid: 50 g/L, 55.degree. C., 50 seconds; Voltage: 50 V Water washing Plating Iron plating [0004] However, the aforementioned conventional plating method has the following problems. [0005] According to the conventional plating method, insoluble matters (smut) in an aluminum alloy generated in the alkaline-etching step are dissolved and removed (pickling) by making use of a mixed solution composed of nitric acid, hydrofluoric acid and sulfuric acid. However, the use of nitric acid in this pickling step is undesirable because of the regulations on nitrogen in view of the problem of eutrophication of sea water. The use of hydrofluoric acid is also undesirable since hydrofluoric acid is a Class 1 designated substance specified by the PRTR (Pollutant Release and Transfer Register). Therefore, there is a strong demand to restrict the use of nitric acid as well as hydrofluoric acid in order to minimize the negative environmental effects. Accordingly, it is strongly desired to develop a method of applying plating (pretreatment) to aluminum alloy materials which does not necessitate the use of nitric acid and hydrofluoric acid. [0006] Furthermore, the nonuse of nitric acid and hydrofluoric acid as much as possible is desirable not only for the purpose of avoiding the natural environmental problems mentioned above, but also for the well-being of workers, e.g., for ensuring the safety of workers dealing with the pretreatment for plating. [0007] The conventional plating method is also problematic because the desmutting treatment by means of pickling mentioned above is low in stability and hence the depth of etching (which has much to do with the adhesion of plating) tends to fluctuate. The administration of the desmutting treatment is very difficult because of its instability. As a result, it is often impossible to secure sufficient anchoring effects on the plating that has been applied to the aluminum alloy material, thus rendering the plating defective as regards adhesion. [0008] Additionally, because the chemicals (a mixed solution composed of nitric acid, hydrofluoric acid and sulfuric acid) employed in the pickling have a short life-span and because transforming the waste water containing hydrofluoric acid into harmless water takes a considerably long time, the cost of the chemicals and that for the waste water treatment are high. BRIEF SUMMARY OF THE INVENTION [0009] The present invention has been made in view of the problems mentioned above and, therefore, some of the objects of the present invention are to provide a method of applying plating to an aluminum alloy material which makes it unnecessary to employ nitric acid and hydrofluoric acid in the pretreatment for plating, which in turn minimizes the negative environmental effects, improves the working environment for pretreatment personnel, reduces the costs for chemicals and wastewater treatment, and secures excellent adhesion of the plated layer. [0010] With a view to achieving the aforementioned objects, there is provided, according to one aspect of the present invention, a method of applying plating to an aluminum alloy material, which essentially comprises a step of cathodic acid electrolysis as a pretreatment for the plating for removing insoluble matters in the aluminum alloy generated in a previous alkaline-etching step. [0011] In one embodiment, the method of applying plating to an aluminum alloy material comprises the steps of: degreasing the aluminum alloy material; subjecting the aluminum alloy material thus degreased to an alkali-etching treatment; subjecting the aluminum alloy material thus alkali-etched to cathodic acid electrolysis; subjecting the aluminum alloy material thus electrolyzed to an anodic oxidation treatment; and applying plating to the aluminum alloy material thus anodically oxidized. [0012] Preferably, the cathodic acid electrolysis is performed in a solution of ferric sulfate with the aluminum alloy material being employed as a cathode. [0013] The aluminum alloy material may be a cylinder for an internal combustion engine (e.g., a cylinder for a small air-cooled two-stroke gasoline engine) wherein the plating is applied to the sliding surface of the piston of the cylinder. [0014] The cylinder for an internal combustion engine according to another aspect of the present invention is featured in that an iron plating is applied to the sliding surface of the piston according to the aforementioned plating method. [0015] The method of applying plating to an aluminum alloy material according to the present invention is featured in that the insoluble matters (smut: Si, Cu, Fe, Mn, etc.) generated in the previous alkaline-etching step are removed not by means of pickling (which has been conventionally employed as a pretreatment for plating) but by means of cathodic acid electrolysis. More specifically, the aluminum alloy material is employed as an anode, and the cathodic acid electrolysis is performed in a solution of ferric sulfate to thereby physically remove the insoluble matters by taking advantage of hydrogen gas to be generated in the acid electrolysis. Therefore, it is no longer necessary to employ nitric acid and hydrofluoric acid in the pretreatment for plating. As a result, it is now possible to minimize the environmental load, to improve the working environment for pretreatment personnel, and to reduce the costs for chemicals and waste water treatment. [0016] Furthermore, since the depth of etching is determined by the treatment conditions (the concentration of a chemical to be employed (caustic soda, etc.), temperature and time) in the alkaline-etching step, and the etching does not proceed in the step of cathodic acid electrolysis as only hydrogen gas is permitted to generate in the cathodic acid electrolysis, it is possible to easily and accurately control the depth of etching. As a result, it is possible to realize high anchoring effects of the plated layer that has been applied to the aluminum alloy material, resulting in improved adhesion (biting property) of plating. BRIEF DESCRIPTION OF THE DRAWINGS [0017] FIG. 1 is a scanning electron microphotograph illustrating the surface of aluminum alloy material after a degreasing treatment in one embodiment of the method of applying plating to an aluminum alloy material according to the present invention. [0018] FIG. 2 is a scanning electron microphotograph illustrating the surface of aluminum alloy material after an alkaline-etching treatment in one embodiment of the method of applying plating to an aluminum alloy material according to the present invention. [0019] FIG. 3 is a scanning electron microphotograph illustrating the surface of aluminum alloy material after a cathodic acid electrolysis in one embodiment of the method of applying plating to an aluminum alloy material according to the present invention. [0020] FIG. 4 is a scanning electron microphotograph of a cross-section of the surface of aluminum alloy material after an Fe plating in one embodiment of the method of applying plating to an aluminum alloy material according to the present invention. [0021] FIG. 5 is a cross-sectional view of a Schnurle scavenging type small air-cooled two-stroke gasoline engine. Continue reading about Plating method for aluminum alloy material... Full patent description for Plating method for aluminum alloy material Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Plating method for aluminum alloy material patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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