JP2012057222A - Pretreatment method for plating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pretreatment method for plating, by which the number of steps in a pretreatment for plating, that is applied to an aluminum alloy, is reduced.SOLUTION: As a treatment solution for removing a deteriorated layer and aluminum alloy components, a mixed solution comprising sulfuric acid having a concentration of 10-50 vol% and acidic ammonium fluoride having a concentration of 10-100 g/L or potassium fluoride having a concentration of 10-70 g/L or a mixed solution comprising phosphoric acid having a concentration of 50-85 vol% and acidic ammonium fluoride having a concentration of 10-100 g/L or a mixed solution comprising phosphoric acid having a concentration of 10-40 vol%, nitric acid having a concentration of 3-12 vol% and acidic ammonium fluoride having a concentration of 10-100 g/L is used.

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 Patent Document 1, two processes can be completed in one process by using an acid etchant that is a mixture of nitric acid, sulfuric acid, and ammonium ammonium fluoride (acidic ammonium fluoride) as the treatment liquid used for the above etching and pickling. Proposals have been made.

Patent Document 2 discloses a fluorine compound such as copper ion, nitric acid, and acidic ammonium fluoride (NH ₄ F · HF) as a processing solution for simultaneously etching a metal film made of silver or a silver alloy and a transparent conductive film such as ITO. Has been proposed.

Japanese Patent Laid-Open No. 11-193481 JP 2009-206462 A

The acidic etching solution disclosed in Patent Document 1 is a mixture of nitric acid and sulfuric acid, and even when acidic ammonium fluoride is contained, the oxidizing power is excessively strong and a passive film is formed on the surface of the aluminum alloy and etching proceeds. It becomes difficult to do.

  The etching solution disclosed in Patent Document 2 contains nitric acid and acidic ammonium fluoride, but forms a passive film on the surface of the aluminum alloy as described above.

In order to solve the above-mentioned problems, the first invention of the present application is a pretreatment method for plating in which the surface of the aluminum alloy is degreased, the altered layer on the surface is removed and the aluminum alloy component is removed, and then a base film is formed on the surface. As a treatment liquid for removing the deteriorated layer and the aluminum alloy component, sulfuric acid having a concentration of 10 vol% to 50 vol% and acidic ammonium fluoride having a concentration of 10 g / l (liter) to 100 g / l or a concentration of 10 g By using a mixed solution of potassium fluoride of / l or more and 70 g / l or less, the deteriorated layer and the aluminum alloy are removed in one step.
In the present invention, the concentration (vol%) of sulfuric acid (phosphoric acid) is 98% sulfuric acid (phosphoric acid) diluted with water. For example, 10 vol% means that 900 ml of water is added to 100 ml of 98% sulfuric acid. Indicates. The acidic ammonium fluoride having a concentration of 10 g / l indicates that 10 g of acidic ammonium fluoride is dissolved in 100 ml of sulfuric acid and 1000 ml of sulfuric acid with 900 ml of water.

The plating pretreatment method according to the second invention of the present application is a treatment liquid for removing the deteriorated layer and removing the aluminum alloy component, and phosphoric acid having a concentration of 50 vol% to 85 vol% and a concentration of 10 g / l to 100 g / l. 1 or less of a mixed solution of acidic ammonium fluoride is used.

Moreover, the plating pretreatment method according to the third invention of the present application provides phosphoric acid having a concentration of 10 vol% or more and 40 vol% or less and a concentration of 3 vol% or more and 12 vol% or less as the treatment liquid for removing the deteriorated layer and removing the aluminum alloy component. A mixed solution of nitric acid and ammonium acid fluoride having a concentration of 10 g / l or more and 100 g / l or less is used.

According to the present invention, the removal of the deteriorated layer and the removal of the aluminum alloy component by the alkali etching solution 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 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 are performed in one step, and the formation of the zinc undercoat is also performed in one step.

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 by the active oxygen generated by the electrolysis, a dense Zn-O-Al film is formed. To form.

Focusing on sulfuric acid, phosphoric acid, nitric acid, acidic ammonium fluoride or potassium fluoride as a treatment liquid for removing the altered layer and removing the aluminum alloy component in one step, a suitable range was verified by combining these.

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.
The following table shows the results of verification.

  As is clear from the above (Table 1) to (Table 6), when a mixed solution of sulfuric acid and acidic ammonium fluoride is used, the concentration of sulfuric acid is 10 to 50 vol%, and the concentration of acidic ammonium fluoride is 10 It is preferable to set it to -100 g / l. Also, from Table 7 to Table 12, it can be seen that potassium fluoride may be used instead of acidic ammonium fluoride.

  Next, the results when a mixed solution of sulfuric acid and ammonium acid fluoride is used as the etching solution are shown in (Table 13) to (Table 18).

As apparent from the above (Table 13) to (Table 18), when a mixed solution of phosphoric acid and acidic ammonium fluoride is used, the concentration of phosphoric acid is 50 to 85 vol%, and the concentration of acidic ammonium fluoride is the concentration. Is preferably 10 to 100 g / l.

Next, the results when using a mixed solution of phosphoric acid, nitric acid, and acidic ammonium fluoride as an etching solution are shown in (Table 19) to (Table 24). Here, the ratio of phosphoric acid and nitric acid is set to 10: 3, and the acid concentration in the table is vol% of phosphoric acid and nitric acid combined.

As is clear from the above (Table 19) to (Table 24), when a mixed solution of phosphoric acid, nitric acid and acidic ammonium fluoride is used, the total amount of phosphoric acid and nitric acid (10: 3) is 13 to 52 vol. %, And the concentration of acidic ammonium fluoride is preferably 10 to 100 g / l.

  In the verification, the liquid temperature was set to 70 ° C. and the processing time was set to 60 seconds. However, the same result was obtained even when the liquid temperature was reduced to 50 ° C. and the processing time was reduced to 30.

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, removal of the altered layer on the surface and removal of the aluminum alloy component are carried out. Thereafter, in the pre-plating treatment method for forming a base film on the surface, the removal of the altered layer and the removal of the aluminum alloy component are performed. As the treatment liquid, a mixed liquid of sulfuric acid having a concentration of 10 vol% to 50 vol% and acidic ammonium fluoride having a concentration of 10 g / l to 100 g / l or potassium fluoride having a concentration of 10 g / l to 70 g / l is used. Thus, the plating pretreatment method is characterized in that the deteriorated layer and the aluminum alloy component are removed in one step. After degreasing the surface of the aluminum alloy, removal of the altered layer on the surface and removal of the aluminum alloy component are carried out. Thereafter, in the pre-plating treatment method for forming a base film on the surface, the removal of the altered layer and the removal of the aluminum alloy component are performed. By using a mixed solution of phosphoric acid having a concentration of 50 vol% or more and 85 vol% or less and ammonium acid fluoride having a concentration of 10 g / l or more and 100 g / l or less as the treatment liquid, the alteration layer is removed and the aluminum alloy in one step. A plating pretreatment method comprising removing a component. After degreasing the surface of the aluminum alloy, removal of the deteriorated layer on the surface and removal of the aluminum alloy component are performed, and thereafter, in the pretreatment method for plating, the removal of the deteriorated layer and the aluminum alloy component are performed. As a treatment liquid for removing water, a mixed liquid of phosphoric acid having a concentration of 10 vol% to 40 vol%, nitric acid having a concentration of 3 vol% to 12 vol%, and acidic ammonium fluoride having a concentration of 10 g / l to 100 g / l is used. Thus, the plating pretreatment method is characterized in that the deteriorated layer and the aluminum alloy component are removed in one step.

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