JPS6167770A - Plating method of magnesium and magnesium alloy - Google Patents

Abstract

PURPOSE:To execute Ni plating with high adhesiveness and excellent corrosion resistance by etching chemically Mg or the alloy thereof, treating the same with a fluoride and neutralizing the same with an alkali then subjecting the Mg or the alloy thereof to the electroless Ni plating with the liquid contg. no sulfuric acid and chloride ions. CONSTITUTION:The Mg or the alloy thereof is treated respectively by the chemical etching liquid contg. pyrophosphate, nitrate and sulfate without contg. chromate ions, the alkali neutralizing liquid contg. hypophosphite and aq. ammo nia soln. and the electroless Ni plating contg. nickel oxycarboxylate, pyro phosphate, hypophosphite and fluoride without contg. sulfate ions and chloride ions in the plating method of the Mg or the alloy thereof including stages for etching chemically the Mg or the alloy thereof, treating the same with the fluoride and subjecting the same to the neutralization with the alkali, then to the electroless Ni plating. The Mg and the alloy thereof are thus plated with the high adhesiveness and corrosion resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for plating magnesium and magnesium alloys with good adhesion and corrosion resistance.

[Conventional wave 4ij] Magnesium has a specific gravity that is about two-thirds that of aluminum, and is used as a lightweight metal.

However, it is highly chemically active, and even if the surface is processed, polished, or chemically activated, an oxide film will immediately form, making it extremely difficult to plate the magnesium surface with good adhesion.

As described above, the so-called Dow method developed by the Dow Chemical Company is known as a surface treatment method for magnesium or magnesium alloys in which it is difficult to obtain an adhesive plating. The Dow method includes an electroplating method (Dow plating method) in which the desired plating is performed after pretreatment, zinc substitution, and copper bronze strike, and an electroless nickel plating method. As electroless nickel plating method,
A method of performing electroless nickel plating after applying curing copper strike by the Dow plating method, and Kano O3-11NO
After chemical etching with a mixed solution of 3, followed by hydrofluoric acid treatment, electroless nickel plating is applied to hi! A method has been proposed. Also, Special Publication No. 37-9800 and Special Publication No. 40-
] No. 722 L;I', , CrO3-11NO
A method (GAT method) is disclosed in which the material is etched with a-11F mixed solution, treated with hydrofluoric acid, and then subjected to alkali neutralization, followed by electroless nickel plating.

In the GAT method, the M[F, film formed on the magnesium surface by hydrofluoric acid treatment is removed from Mg by an alkali neutralization treatment.
1ll', and Mg(Oll)z, improving the adhesion of electroless nickel plating.Since an alkaline electroless nickel plating bath is used, magnesium is It has the advantage that corrosion does not occur.

However, with these conventional electroless nickel methods, it is not possible to obtain plating with good adhesion, and because acidic chromic acid solution is used for chemical etching, the magnesium surface becomes rough due to erosion, and the appearance of the plating deteriorates. Not only will it get worse;
Since a large amount of hexavalent chromium is used, there is a risk of causing drainage pollution, which is not desirable. Also, the Dow method, /l
(1-Zn-MU die cuff, 1-When applied to gold alloy plating, the zinc joint itself is extremely unreliable, and plating with good adhesion cannot be obtained.

[Purpose of the invention]

It is an object of the present invention to provide a method for applying an adhesive and corrosion-resistant undercut to magnesium and magnesium alloys.

[Structure of the invention]

When plating magnesium or magnesium alloy, the only thing that impairs its adhesion is MgO1M1! +J
6. These are intermetallic compounds such as □, the potential difference that occurs between the substrate and the plating layer, and corrosive media (water, oxygen, various anions, etc.). The inventor of the present invention has carried out extensive research with these points in mind, and has now completed the present invention. The present invention involves chemically etching magnesium or magnesium alloys, treating them with fluoride, neutralizing them with alkali, and then chemically etching magnesium or magnesium alloys with fluoride.
In a magnesium or magnesium alloy plating method that includes electrolytic nickel plating, the chemical etching solution contains pyrophosphate, nitrate, and sulfate but does not contain chromate ions, and the alkaline neutralization solution contains hypophosphorous acid. The electroless nickel plating solution contains salt and aqueous ammonia, and the electroless nickel plating solution contains nickel oxycarboxylate, pyrophosphate, hypophosphite and fluoride.
A method for plating magnesium or magnesium alloy, characterized by not containing sulfate ions and chloride ions.

The present invention will be explained in detail below.

When carrying out the method of the present invention, surface polishing and surface degreasing are first performed, if necessary. Surface polishing is performed by removing as much as possible of hot water wrinkles, pores, and other defects existing on the surface of the material by polishing with an emery cloth, etc., and then mirror-finishing the material with a 1-Ribori cloth. A satin finish may be applied by blasting. Next, after preliminary cleaning with an organic solvent, dirt deposited on the surface is thoroughly removed using an alkaline n+h fat agent. If necessary, cathodic electrolytic degreasing may be used in combination.

After degreasing, chemical etching is performed. The etching solution used in the present invention contains pyrophosphate, nitrate, and sulfate. As the salt, sodium salt, potassium salt, or ammonia J salt is preferred. The yield of pyrophosphate is 50 to 500 g/C1, preferably 100
~200 g/β is very suitable. The concentration of nitrate is 20
~300g/ff, good)E or 50-200g/I
f is appropriate. The concentration of sulfate is 5 to 100 g/x, preferably 10 to 50 g/ Approximately 1 minute to 3 minutes is appropriate.

This chemical etching process removes the acid present on the surface of the material. Furthermore, the surface of the material is not so roughened, and the potential of each portion of the surface is made uniform. At this time, pyrophosphate and sulfate act as etching agents, and nitrate acts as a corrosion inhibitor for magnesium. Pyrophosphate also forms a phosphate film as a corrosion protection film on the surface of the material, preventing corrosion of the material in air and water.

After chemical etching and washing with water, the material is treated with fluoride. This treatment is to more completely remove impurities such as Shi0, Mg+7Aff12, and form a magnesium fluoride film. As a fluoride treatment liquid,
For example, 70%■■F, or LJ85% phosphoric acid 20
A solution containing 0 g/β and 100 g/l of N11411F2 is used. A treatment temperature of room temperature is sufficient, and a treatment time of approximately 30 to 90 seconds is appropriate.

Next, after washing with water, alkali neutralization treatment is performed. The alkaline neutralization solution of the present invention contains hypophosphite and aqueous ammonia. As the salt, sodium salt, potassium salt, or ammonium salt is preferred. Of hypophosphite? Agricultural degree is 5-50 g//! , preferred L <i; i ] 0
〜30 g/(l is appropriate.The concentration of ammonia water is 11.28% by weight. 5,100 m 1 /
i2, preferably 10 to 30 m (1/1.
0-30g/7! is appropriate. As the oxycarboxylic acid, citric acid, malic acid, lactic acid, glycolic acid, succinic acid, etc. can be used. Salts of oxycarboxylic acids include sodium salts, potassium salts,
Ammonium salts and the like are preferred. In this way, plating can be started smoothly by containing an oxycarboxylic acid salt in the neutralizing solution and keeping it close to the S and I compositions of the electroless nickel plating solution in the next step. A treatment temperature of 6 years old and room temperature is sufficient, and a treatment time of about 30 to 120 seconds is appropriate.

Since the alkaline neutralization liquid of the present invention contains a reducing agent,
Not only does it neutralize the fluoride treatment liquid components remaining on the surface of the material, but it also effectively prevents oxidation on the surface of the material.

Next, electroless nickel plating treatment is performed without washing with water. By omitting the water washing step, the occurrence of oxidation or corrosion on the surface of the material, which normally tends to occur during airborne stay or water washing, is significantly reduced.

The electroless nickel plating solution used in the present invention contains nickel oxycarboxylate, pyrophosphate, hypophosphite, and fluoride. As the oxycarboxylic acid, the aforementioned oxycarboxylic acids can be used. As the pyrophosphate, hypophosphite and fluoride, sodium salt, potassium salt, ammonium salt and the like are preferred.

The electroless nickel plating solution used in the present invention does not substantially contain anions such as sulfate ions and chloride ions, which are highly corrosive to magnesium. The appropriate concentration of nickel oxycarboxylate is 15 to 35 g/A, preferably 20 to 30 g/II. The concentration of pyrophosphate is 30-100 g/l, preferably 30-7
0g/7! is appropriate. The concentration of hypophosphite is 15-35 g/l, preferably Bat 20-30 g/7! is appropriate. Fluoride concentration &;l: 2-20g/1. ．． Preferably 5~
10 g/p is appropriate. In the present invention, electroless nickel plating? It is preferable that pl+ at night conforms to Alkaline's law, and particularly preferably a range of pl+ of 9.5 to 10.5. It is appropriate that the temperature of the treatment bath is 50 to 65°C and the treatment time is 2 to 10 minutes.

After electroless nickel plating, wash with water. The material thus plated according to the method of the present invention can be used as it is as a plated product, or it can be used as a base for further other plating, such as acidic electroless plating or electroplating. .

EXAMPLES Next, the present invention will be explained in more detail by showing examples. The ingredients of the materials used in the following examples are as follows.

Bow 1 1 1 g Example 1 AZ-91,8 Sogetsu (J I
Plating was applied to S-MDC/IB-bosotochanhard die casting) using the Dow method, the GAT method, and the method according to the present invention shown in Table 1.

As a result, the following became clear.

(2) According to the Dow method, the surface that has been smoothed by Chofu polishing is roughened by chemical etching, exposing surface defects in the material. Furthermore, due to the insoluble film (MgF2) formed on the surface by the hydrofluoric acid treatment in the next step, the electroless nickel plating reaction will start soon (60-120
(reaction started after a few seconds had elapsed), not only was it likely to result in non-uniform plating, but also good adhesion of the plating could not be obtained.

2) In the GAT method, the surface of the material is roughened due to chemical etching at the same time as the DOW method, but the electroless nickel plating reaction starts quickly and uniformly. However, the surface of the material was attacked by the plating solution during the initial stage of the reaction (30 to 60 seconds), and after plating, it was subjected to a haking process at 200°C for 1 hour.
Even if the coating is applied to improve the adhesion of the plating,
Blisters occurred in some areas due to poor adhesion.

3) The plating using the method according to the present invention not only had a beautiful appearance without any roughness on the surface of the material due to etching, but also had good adhesion and porosity.

Example 2 Zandocath 1- (sand casting) AZ-92, A (J l
As a result of plating 5-MC-3) using the plating method according to the present invention shown in Table 1, a plating having good adhesion and corrosion resistance was obtained.

Since Santocast has large crystal grains and many segregated areas, it is difficult to obtain a uniform surface condition unless chemical etching and fluoride treatment are repeated.

Example 3 AZ-63 (JIS-MC-1) and ZK-61 (JIS-MC-1)
As a result of plating S-MC-7) using the method according to the present invention shown in Table 1, plating with good appearance, adhesion, and corrosion resistance was obtained.

In addition, in the examples, good and mono-edible properties refer to test pieces with electrolytic nickel plating (Dow method) and acidic electroless nickel plating (10μ thick) after electroless nickel plating. ) with Tess(・Peace(G)
(AT method and method of the present invention) that can withstand a salt spray test for 150 hours or more.

〔Effect of the invention〕

According to the present invention, it is possible to form a transparent plating film with good adhesion and corrosion resistance on the surface of magnesium or a magnesium alloy. Since pl+ of the electroless nickel plating solution used in the final step of the present invention is on the alkaline side, the P content of the precipitate is smaller than when an acid bath is used. For this reason, the plating film obtained by the method of the present invention has poor adhesion to the plating film to be applied next.

Since the method of the present invention does not include an electrolytic process, it is possible to uniformly form a plating film with strong coating power on the back surface of the member to be treated, screw holes, hook parts, etc. Can be directly plated.

The plating film obtained by the method of the present invention can be used as a base for other acidic electroless plating or electroplating to obtain various plating films with poor adhesion, corrosion resistance, and abrasion resistance, depending on the purpose of use. can.

Claims (1)

[Claims] A method for plating magnesium or a magnesium alloy, which includes the steps of chemically etching magnesium or a magnesium alloy, treating it with a fluoride, neutralizing it with an alkali, and then performing electroless nickel plating, wherein the chemical etching solution is , pyrophosphate, nitrate and sulfate, but no chromate ions; the alkaline neutralizing solution contains hypophosphite and aqueous ammonia; the electroless nickel plating solution contains nickel oxycarboxylate, pyrophosphate Contains salt, hypophosphite and fluoride;
A method for plating magnesium or magnesium alloy, characterized by not containing sulfate ions and chloride ions.