JP2012057224A - Method for pre-plating treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for pre-plating treatment with reduced number of pre-plating treatment processes applied to aluminum alloy.SOLUTION: Sulfuric acid having the concentration of 10 to 50 vol.% or the mixed acid of phosphoric acid having the concentration of 10 to 40 vol.% and sulfuric acid having the concentration of 3 to 12 vol.% is used as an electrolyte for removing an altered layer and aluminum alloy components by anode electrolysis.

Description

  The present invention relates to a pretreatment method for plating a surface of an aluminum alloy member such as a cylinder block.

  Ni-SiC plating is applied to the piston sliding surface of the aluminum alloy cylinder block. As this pretreatment for plating, a zinc undercoat is generally formed. In order to form this zinc undercoat, as shown in FIG. 2, the oil film adhering to the cylinder block surface is removed by degreasing, and then the Al oxide film, processed fluidized layer or oil-containing phase on the cylinder block surface is removed. Etch the denatured layer with an alkaline solution, and remove the alloy components remaining on the cylinder block surface by pickling. There is known a double zinc replacement method in which a passive film containing zinc is used, and this passive film is replaced with a dense base film made of Zn—O—Al.

  In addition, by immersing a metal product in the electrolyte and flowing a direct current using the metal product as an anode or a cathode, oxygen or hydrogen is generated from the product surface, and this oxygen or hydrogen removes dirt adhering to the product surface. A cleaning method is also conventionally known.

  The above double zinc replacement method is not efficient because there are many steps such as alkali etching, pickling, zinc coating replacement, acid treatment, zinc coating replacement, and a water cleaning step is added between the steps. In view of this, Patent Documents 1 and 2 propose that alkali etching and pickling be performed in one step.

  Patent Document 1 describes that anodic etching is performed on the surface of an aluminum alloy so that silicon protrudes from the surface of the aluminum alloy, and a plating layer is formed on the surface from which the silicon protrudes.

  Patent Document 2 proposes that an acid etching solution that is a mixture of nitric acid, sulfuric acid, and ammonium ammonium fluoride (acidic ammonium fluoride) is used as a processing solution for etching and pickling. Has been made.

JP-A-11-001795 Japanese Patent Laid-Open No. 11-193481

  In the case of conventional alkali etching and pickling, when the aluminum alloy surface is excessively etched by alkali etching, a deep groove is formed, and a gap is formed between the zinc substitution film and the aluminum alloy surface formed thereafter, Adhesion decreases.

  Moreover, the conventional electrolytic cleaning uses an alkaline electrolyte, and the alloy components cannot be removed. Electrolytic cleaning using an acid as an electrolytic solution is also known, but in this case, it is cathodic electrolysis and there is a risk of contamination.

Further, in the method disclosed in Patent Document 1, in the portion where the elongated silicon crystal protrudes densely from the aluminum alloy surface as shown in FIG. May be easier to do.

The acidic etching solution disclosed in Patent Document 2 is a mixture of nitric acid and sulfuric acid. Even if acidic ammonium fluoride is contained, the oxidizing power is excessively strong and a passive film is formed on the surface of the aluminum alloy. It becomes difficult to progress.

In order to solve the above problems, the first invention of the present application is to degrease the surface of the aluminum alloy, and then to remove the altered layer on the surface and remove the aluminum alloy component by anodic electrolytic treatment. Of sulfuric acid with a concentration of 10 to 50 vol%, a current density of 10 to 100 A / dm ² , and an electrolysis time of 5 to 30 seconds.
In the present invention, the sulfuric acid concentration (vol%) is 98% sulfuric acid diluted with water. For example, 10 vol% means that 900 ml of water is added to 100 ml of 98% sulfuric acid.

In the second invention of the present application, as the anodic electrolytic treatment conditions, the electrolytic solution is a mixed solution of phosphoric acid having a concentration of 10 to 40 vol% and nitric acid having a concentration of 3 to 12 vol%, and the current density is 10 to 100 A / dm ^2. Electrolysis time: 10 to 60 seconds.

In the above electrolytic treatment, the etching soot may be effectively removed by subjecting the aluminum alloy surface to ultrasonic treatment while the aluminum alloy surface is immersed in the electrolytic solution.

According to the present invention, the alteration layer removal with an alkaline etching solution and the removal of the aluminum alloy component by pickling are conventionally performed in two steps, but this can be performed in one step. As a result, the cycle time of the plating pretreatment is shortened and the efficiency is greatly improved. In addition, investment in dedicated and general-purpose facilities can be reduced with the reduction in the number of processes.

Schematic of plating pretreatment process according to the present invention Schematic diagram of conventional plating pretreatment process Diagram explaining problems of conventional plating pretreatment Illustration explaining the adhesion test method

Embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, in this embodiment, the removal of the deteriorated layer and the removal of the aluminum alloy component (including dissolution of the smut) are performed in one step by electrolytic treatment, and the formation of the zinc undercoat is also performed in one step. Like to do.

In this embodiment, the formation of the zinc undercoat is performed by electrolysis in the same solution, that is, by anodic electrolysis of a rough zinc coat and bonding Zn element and Al element by active oxygen generated by the electrolysis. And a dense Zn—O—Al film is formed.

As the electrolytic solution for anodic electrolysis in which the alteration layer and the aluminum alloy component are removed in one step, sulfuric acid is used in the first invention, and a mixed solution of phosphoric acid and nitric acid is used in the second invention.
Below, the experimental result which changed the density | concentration (vol%) of electrolyte solution, current density (A / dm < ² >), process time, and process temperature is shown.

The determination as to whether or not it was suitable was made based on the adhesion of the Ni—SiC plating film. Moreover, verification was performed by JIS-H8504-11 (extrusion test method) shown in FIG.
For the extrusion test method, a flat bottom hole with a diameter of φ6.5 mm was left from the back side with respect to the plated surface, and then a sample was placed on a cradle with a hole with a diameter of φ25 mm, and a pin with a diameter of φ6.3 mm Is inserted into the hole in the flat bottom and punched out.
A change in the state of plating on the punched piece part was examined, and adhesion ◎ ○ × was determined.
◎ indicates that no peeling of the plating is observed, ○ indicates that peeling of the plating is partially observed, and × indicates that peeling of the plating is observed on the entire circumference.
Tables 1 to 6 correspond to the first invention, and Tables 7 to 12 correspond to the second invention.

As is clear from the above (Table 1) to (Table 6), when anodic electrolysis is performed using sulfuric acid as the electrolytic solution, the concentration is 10 to 50 vol% and the current density is 10 to 100 A / dm ^2. preferable.
The electrolytic solution temperature was 70 ° C. and the treatment time was 20 seconds. However, the electrolytic solution temperature was 50 ° C. or more, and the electrolysis time was preferably 5 to 30 seconds.

In the experiment in which the electrolyte was a mixed acid of phosphoric acid and nitric acid, the ratio of phosphoric acid and nitric acid was 1: 1, but the ratio of nitric acid to phosphoric acid was the same in the range of 0.5 to 2.0. was gotten. Further, the current density (A / dm ² ) is preferably 10 to 100 A / dm ² as in the case of sulfuric acid, but in the experiment, it was 80 A / dm ² . The electrolyte temperature was 40 ° C. and the treatment time was 30 seconds, but the electrolyte temperature was preferably 25 ° C. or more and the electrolysis time was preferably 10 to 60 seconds.

As is clear from the above (Table 8) to (Table 12), when an anodic electrolysis treatment is performed using a mixed acid of phosphoric acid and nitric acid as an electrolytic solution, the concentration of phosphoric acid is 10 to 40 vol%, The concentration is preferably 3 to 12 vol%.

The plating pretreatment process according to the present invention can be used as a pretreatment for plating applied to an aluminum alloy member such as an engine cylinder block.

Claims (3)

After degreasing the surface of the aluminum alloy product, removing the altered layer on the surface and removing the aluminum alloy component, and then, in the pre-plating treatment method for forming a base film on the surface, the removal of the altered layer and the aluminum alloy component A plating pretreatment method characterized in that the removal is electrolytically treated under the following conditions.
Anode: Aluminum alloy product Electrolytic solution: Sulfuric acid current density of 10 vol% or more and 50 vol% or less: 10 A / dm ² or more and 100 A / dm ² or less Electrolysis time: 5 seconds or more and 30 seconds or less After degreasing the surface of the aluminum alloy product, removing the altered layer on the surface and removing the aluminum alloy component, and then, in the pre-plating treatment method for forming a base film on the surface, the removal of the altered layer and the aluminum alloy component A plating pretreatment method characterized in that the removal is electrolytically treated under the following conditions.
Anode: Aluminum alloy product Electrolyte: concentration 10 vol% or more 40 vol% or less of phosphoric acid + concentration 3 vol% or more 12 vol% or less of nitrate current density: 10A / dm ² or more 100A / dm ² or less electrolysis time: 60 seconds or less 10 seconds or more 3. The plating pretreatment method according to claim 1 or 2, wherein ultrasonic treatment is performed while the aluminum alloy surface is immersed in an electrolytic solution.

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