US20080156653A1

US20080156653A1 - Cyanide-free pre-treating solution for electroplating copper coating layer on magnesium alloy surface and a pre-treating method thereof

Info

Publication number: US20080156653A1
Application number: US11/646,971
Authority: US
Inventors: Ching-An Huang; Tsung-Hsing Wang; Kung-Liung Chen
Original assignee: Chang Gung University CGU
Current assignee: Chang Gung University CGU
Priority date: 2006-12-28
Filing date: 2006-12-28
Publication date: 2008-07-03

Abstract

A pre-treating solution for electroplating magnesium alloy surface contains copper ions, a complexing agent and an additive, wherein the complexing agent is selected from potassium sodium tartrate, potassium tartrate, sodium tartrate, tartaric acid, and dissolvable salts derivative from tartaric acid and the additive is selected from sodium phosphate, sodium hypophosphite, phosphoric acid and dissolvable salts derivative from phosphoric acid or hypophosphite acid. The magnesium alloy is dipped in the pre-treating solution and electroplated with a copper coating layer. Then, the magnesium alloy is further dipped in a copper sulfate solution for thickening the copper coating layer and lastly coated with an anti-corrosion metal layer. Thereby, magnesium alloy has excellent anti-corrosion and anti-wearing efficiency and varnish appearance. Moreover, the pre-treating solution contains no cyanide and thus is low toxic and safe to operator during electroplating and to environment after discharging.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a pre-treating solution, and more particularly to a pre-treating solution without toxic materials. A pre-treating method of the pre-treating solution is also disclosed.
2. Description of Related Art
Magnesium alloy is getting popular to apply on 3C products, mobile industry, and other applicable objects since the magnesium has low density (1.74 g/cm³) and high strength to reduce total weight and enhance appearance of the coated object. Moreover, the magnesium alloy has other advantages in thermal-resistance and thermal-dispersion, especially in the thermal-conduction. However, the magnesium alloy has low reduction electricity potential and active chemical reaction capability that make its application limited. Further disadvantage of the magnesium alloy is that the corrosion resistance of the magnesium alloy is insufficient so that the magnesium alloy needs another surface treatment.
Conventional surface treatment of magnesium alloy includes anodic treatment, synthesizing treatment and metal-coating treatment (e.g. nickel-coating treatment) etc. Wherein, the anodic treatment and the synthesizing treatment are to generate an anti-corrosion oxide layer on surface of the magnesium alloy but the oxide layer has insufficient corrosion resistance and needs further processes such as paint-spraying to achieve anti-corrosion purposes. The metal-coating treatment not only significantly improves the corrosion resistance of the magnesium alloy but also increase hardness, abrasion resistance and appearance varnish.
The metal-coating treatment on the magnesium alloy is carried out by electroless plating method that is time-consuming and has complex pre-treatments. Moreover, solvents used in the pre-treatments mostly contain toxic acidic materials such as hydrofluoric acid (HF) and chromium trioxide (CrO₃) and cyanide. The complex pre-treatments cause cost increment and the toxic acidic materials may cause damage to environments and human being. Although another optional electroplating method can save more time than the electroless plating method, the electroplating method on the magnesium alloy is at a developing stage and not matured enough. A critical disadvantage of the electroplating method is that corrosion happens easily on the surface of the magnesium alloy no matter in acid or alkaline electroplating solutions. Therefore, the market-available electroplating solution can not directly use in the electroplating method of magnesium alloy. Moreover, the electroless plating method generates a non-conductive layer on the surface of the magnesium alloy and thus can not be applied as a pre-treatment of the electroplating method.
Additionally, two conventional electroplating methods for magnesium alloy are also concerned, one is chemical electroplating that takes formaldehyde as catalyst and the other is current electroplating that applies current to reduce copper ions, wherein the copper cyanide is toxic and acidic.
Therefore, the present invention has arisen to mitigate and/or obviate the drawbacks of the conventional electroplating solutions and methods for electroplating on the magnesium alloy.

SUMMARY OF THE INVENTION

The main objective of the present invention is to provide a cyanide-free pre-treating solution for electroplating magnesium alloy surface, wherein the pre-treating solution is non-toxic and alkaline and enables its operational methods to be simplified.
Another main objection of the present invention is to provide operational methods that make use of the above pre-treating solution for electroplating magnesium alloy surface to form an elementary copper layer.
To achieve foregoing main objectives, the cyanide-free pre-treating solution comprises an aqua solution added with copper ions, a complexing agent and an additive, wherein:
the complexing agent is selected from the group consisting of potassium sodium tartrate, potassium tartrate, sodium tartrate, tartaric acid, and dissolvable salts derivative from tartaric acid; and
the additive is selected from the group consisting of sodium phosphate, sodium hypophosphite, phosphoric acid and dissolvable salts derivative from phosphoric acid or hypophosphite acid.
The operational method comprises steps of:
(a) degreasing: a prepared workpiece made of magnesium alloy is degreased with a degreasing agent to remove oil and dirt from surface of the prepared workpiece;
(b) washing: the prepared workpiece is washed to remove the degreasing agent and to keep the surface of the prepared workpiece clean;
(c) copper electroplating: the prepared workpiece is dipped into a pre-treating solution with auxiliary electrodes and electroplated to obtain a copper coating layer by applying a fixed current from an additional power supplier; and
(d) drying: the pre-treating solution residual on the prepared workpiece is removed from the surface of the workpiece to make the surface dry rapidly.
Because the pre-treating solution is alkaline and contains no toxic materials such as cyanide etc., the pre-treating solution is safe and environmental during treatment of the magnesium alloy surface. Moreover, the pre-treating method using the pre-treating solution facilitates the further nickel-coating treatment of the magnesium alloy.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a pre-treatment of magnesium alloy using a cyanide-free pre-treating solution in accordance with the present invention;

FIG. 2 is a SEM (Scanning Electronic Microscopy) picture showing a copper coating layer on surface of the magnesium alloy;

FIG. 3 is a SEM (Scanning Electronic Microscopy) picture showing a nickel electroplating layer coated on the copper coating layer after an anti-corrosion treatment; and

FIG. 4 is a graph showing testing results of the magnesium alloy before or after copper coating pre-treatment and nickel coating anti-corrosion treatment.

DETAILED DESCRIPTION OF THE INVENTION

A pre-treating solution for electroplating magnesium alloy surface in accordance with the present invention contains copper ions, a complexing agent and an additive, wherein the complexing agent is selected from potassium sodium tartrate, potassium tartrate, sodium tartrate, tartaric acid, and dissolvable salts derivative from tartaric acid and the additive is selected from sodium phosphate, sodium hypophosphite, phosphoric acid and dissolvable salts derivative from phosphoric acid or hypophosphite acid. The magnesium alloy is dipped in the pre-treating solution and electroplated with a first copper coating layer. Then, the magnesium alloy is further dipped in a market-available copper sulfate solution for thickening the copper coating layer (performing a second copper coating layer) and lastly coated with an anti-corrosion metal layer. Thereby, magnesium alloy has excellent anti-corrosion and anti-wearing efficiency and varnish appearance. Moreover, the pre-treating solution contains no cyanide and thus is low toxic, alkaline and safe to operator during electroplating and to environment after discharging.
The pre-treating solution for electroplating magnesium alloy surface comprises: 5 to 50 g/L of copper ions from copper chloride, copper sulfate, or copper pyrophosphate; 25 to 150 g/L of the complexing agent selected from the group consisting of potassium sodium tartrate, potassium tartrate and sodium tartrate; and 5 to 50 g/L of the additive selected from the group consisting of sodium phosphate, sodium hypophosphite and phosphoric acid. Reasonably, the pre-treating solution can be modified to have different preferred compositions as shown in following table:


	component

	Num.	Copper ion	Complexing agent	Additive

1	1.2	g/L	4.8	g/L	1.5	g/L
2	5	g/L	30	g/L	5	g/L
3	1.5	g/L	95	g/L	3.5	g/L
4	100	g/L	10	g/L	2.5	g/L
5	90	g/L	75	g/L	2	g/L
6	10	g/L	68	g/L	4	g/L
7	25	g/L	110	g/L	2.5	g/L
8	10	g/L	130	g/L	10	g/L
9	80	g/L	25	g/L	15	g/L
10	48	g/L	78	g/L	48	g/L
11	150	g/L	38	g/L	23	g/L
12	33	g/L	104	g/L	33	g/L
13	67	g/L	72	g/L	28	g/L
14	50	g/L	250	g/L	45	g/L
15	38	g/L	127	g/L	38	g/L
16	18	g/L	150	g/L	18	g/L
17	33	g/L	125	g/L	7	g/L
18	20	g/L	93	g/L	20	g/L
19	60	g/L	300	g/L	6	g/L
20	11	g/L	138	g/L	10	g/L
21	41	g/L	142	g/L	5	g/L
22	65	g/L	210	g/L	12	g/L
23	95	g/L	45	g/L	17	g/L
24	27	g/L	25	g/L	27	g/L
25	185	g/L	75	g/L	42	g/L

Compositions of the pre-treating solution in serial number of 2, 8, 10, 12, 15, 18, 21 and 24 in the table are mostly preferred.
With reference to FIG. 1, a method of a pre-treating operation to the magnesium alloy is shown and is adapted to form a first copper coating layer on a prepared workpiece made of magnesium alloy by using the pre-treating solution in the present invention. The pre-treating operation comprises steps of:
(a). degreasing:
The prepared workpiece is degreased with a degreasing agent to remove oil and dirt from its surface.
(b). washing:
The prepared workpiece is washed to remove the degreasing agent and to keep the surface clean.
(c) copper electroplating:
The workpiece is dipped into the pre-treating solution with auxiliary electrodes and electroplated to obtain a copper coating layer (the first copper coating layer) thereon by applying a fixed current from an additional power supplier.
(d) drying:
After electroplating, residual solution is removed from the surface of the workpiece to make the surface dry rapidly.
Moreover, a washing step is added into the pre-treating method after the (c) step of copper electroplating.
Wherein, the surface temperature of the workpiece in (c) step of copper electroplating is about 10 to 90° C.
Wherein, the fixed current provided by the additional power supplier has a range from 0.01 to 0.15 ampere per square decimeter.
Wherein, the auxiliary electrodes are made of material selected from the group comprising titanium core coated with platinum, titanium, platinum, graphite and stainless steel.
With further reference to FIG. 1, a preferred embodiment of a pre-treating operation is shown. Before copper electroplating, the workpiece is prepared (10), degreased (11) and washed (12) to make its surface clean. Then, the workpiece, auxiliary electrodes, and the pre-treating solution are inputted into a tank to carry out electroplating (13) with mechanically stir. By applying a fixed current from an additional power supplier, the copper ions in the pre-treating solution obtain electrons to reduce and deposit on the surface of the workpiece so that the workpiece obtains a uniform copper coating layer, i.e. the first copper coating layer. After copper electroplating, the workpiece is washed (14) again and dried (15). The workpiece with the first copper coating layer is further treated with a conventional electroplating process to form a second copper coating layer on the first copper coating layer to obtain the final product. Lastly, the workpiece is further coated with an anti-corrosion metal layer to have excellent anti-corrosion and anti-wearing efficiency and varnish appearance.
With reference to FIG. 2, the final product is observed by Scanning Electronic Microscopy (SEM) to exam the magnesium alloy surface and a cross-section of the coated workpiece. According to FIG. 2, the final product comprises a substrate (20) of the magnesium alloy, a first copper layer (21) and a second copper layer (22), wherein the copper layers (21, 22) are firmly combined with the substrate (20) and have no bubbles therein.
With reference to FIG. 3, the magnesium alloy having the pre-treating operation is further treated with an anti-corrosion electroplating to perform a nickel coating (23) thereon, i.e., the substrate (20) of magnesium alloy already having the first copper layer (21) and the second copper layer (22) further obtains the anti-corrosion nickel layer (23) by use of a conventional nickel-electroplating solution.
With reference to FIG. 4, the magnesium alloy workpiece (AZ61) and its variations after pre-treatment and anti-corrosion treatment are tested in 3.5 wt % NaCl solution by standard anodic polarization measurement and the results indicate that the nickel layer significantly increases anti-corrosion capability of the magnesium alloy.
The cyanide-free pre-treating solution for magnesium alloy surface contains an aqua solution added with copper ions, a complexing agent and an additive, wherein the complexing agent is selected from potassium sodium tartrate, potassium tartrate, sodium tartrate, tartaric acid, and dissolvable salts derivative from tartaric acid and the additive is selected from sodium phosphate, sodium hypophosphite, phosphoric acid and dissolvable salts derivative from phosphoric acid or hypophosphite acid.
Wherein, the copper ions are obtained from copper chloride, copper sulfate, copper pyrophosphate or hydrates of foregoing mentioned salts.
Wherein, concentration of the copper ion is 5 to 50 g/L.
Wherein, concentration of the complexing agent is 25 to 150 g/L.
Wherein, concentration of the additive is 5 to 50 g/L.
According to above description, the cyanide-free pre-treating solution for magnesium alloy surface in accordance with the present invention and its operational method has the following advantages:
1. The conventional electroless method is troublesome in pre-treatment. By using the pre-treating solution with copper ions to carry the pre-treatment out, the following nickel layer can be efficiently applied onto the copper layer so that the active magnesium alloy surface is completely treated with rapidly and simply two-step electroplating procedures.
2. The pre-treating solution in the present invention is alkaline in particular and contains no toxic cyanide, hydrofluoric acid (HF) and chromium trioxide (CrO₃) so that it is safe to human being and environment and causes no pollution during electroplating procedures.
Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.

Claims

1. A pre-treating method for magnesium alloy surface comprising steps of:

(a) degreasing: a prepared workpiece made of magnesium alloy is degreased with a degreasing agent to remove oil and dirt from surface of the prepared workpiece;

(b) washing: the prepared workpiece is washed to remove the degreasing agent and to keep the surface of the prepared workpiece clean;

(c) copper electroplating: the prepared workpiece is dipped into a pre-treating solution with auxiliary electrodes and electroplated to obtain a copper coating layer by applying a fixed current from an additional power supplier; and

(d) drying: the pre-treating solution residual on the prepared workpiece is removed from the surface of the workpiece to make the surface dry rapidly.

2. The pre-treating method as claimed in claim 1 further comprising a washing step after (c) step of copper electroplating.

3. The pre-treating method as claimed in claim 1, wherein the fixed current provided by the additional power supplier has a range from 0.01 to 0.15 ampere per square decimeter.

4. The pre-treating method as claimed in claim 1, wherein the auxiliary electrodes are made of material selected from the group consisting of titanium core coated with platinum, titanium, platinum, graphite and stainless steel.

5. The pre-treating method as claimed in claim 1, wherein surface temperature of the prepared workpiece in (c) step of copper electroplating is 10 to 90° C.

6. The pre-treating method as claimed in claim 1, wherein the workpiece is further treated with another copper electroplating process and a nickel coating process after the step of drying.

7. The pre-treating method as claimed in claim 1, wherein the pre-treatment solution comprises an aqua solution added with copper ions, a complexing agent and an additive.

8. The pre-treating method as claimed in claim 7, wherein the pre-treatment solution comprises

the complexing agent selected from the group consisting of potassium sodium tartrate, potassium tartrate, sodium tartrate, tartaric acid, and dissolvable salts derivative from tartaric acid; and

the additive selected from the group consisting of sodium phosphate, sodium hypophosphite, phosphoric acid and dissolvable salts derivative from phosphoric acid or hypophosphite acid.

9. The pre-treating method as claimed in claim 7, wherein the additive is 5 to 50 g/L in concentration.

10. The pre-treating method as claimed in claim 7, wherein the complexing agent is 25 to 150 g/L in concentration.

11. The pre-treating method as claimed in claim 7, wherein the copper ions are obtained from the group consisting of copper chloride, copper sulfate, copper pyrophosphate and hydrates of foregoing motioned salts.

12. The pre-treating method as claimed in claim 7, wherein the copper ions are 5 to 50 g/L in concentration.

13. A pre-treatment solution for coating a copper layer on a magnesium alloy, the pre-treatment solution comprising an aqua solution added with copper ions, a complexing agent and an additive, wherein

the complexing agent is selected from the group consisting of potassium sodium tartrate, potassium tartrate, sodium tartrate, tartaric acid, and dissolvable salts derivative from tartaric acid; and

the additive is selected from the group consisting of sodium phosphate, sodium hypophosphite, phosphoric acid and dissolvable salts derivative from phosphoric acid or hypophosphite acid.

14. The pre-treating solution as claimed in claim 13, wherein the additive is 5 to 50 g/L in concentration.

15. The pre-treating solution as claimed in claim 13, wherein the complexing agent is 25 to 150 g/L in concentration.

16. The pre-treating solution as claimed in claim 13, wherein the copper ions are obtained from the group consisting of copper chloride, copper sulfate, copper pyrophosphate and hydrates of foregoing motioned salts.

17. The pre-treating solution as claimed in claim 13, wherein the copper ions are 5 to 50 g/L in concentration.