In this paper, the technical factors of zinc alloy and sf-628 cyanide free alkaline copper plating are discussed. The process and operation of alkaline copper plating without cyan are given. This process is worth popularizing.

Key words: zinc alloy, cyanide free alkaline copper plating, pretreatment

1、 Introduction

Sf-628 non cyanide alkaline copper plating has excellent dispersing ability and deep plating ability. It can be easily pre plated and thickened for various types of substrate coatings. The semi bright appearance of the coating is a substitute for the traditional copper cyanide plating process. It has been widely used in Europe and America for several years, and has been recognized by first-class enterprises such as Boeing company in the United States.

In China, due to administrative reasons, cyanide free alkaline copper plating process was mainly focused on the research and development of single electroplating in the past, but its large-scale production and use related technical support were very few, so its promotion and application were limited. In particular, zinc die casting non cyanide alkaline copper after collaborative efforts has not become an effective solution. In our experiments and production applications, sf-628 cyanide free alkaline copper plating process and the company's pre plating process were used in zinc alloy die casting, and excellent adhesion was achieved, so as to further promote the accumulation of useful experience of cyanide free copper technology.

2、 Development of non cyanide alkaline copper plating joint for sf-628 zinc alloy

We know that copper cyanide contained in copper cyanide is a very strong complexing agent, and it is also very effective for scale activator. It can be carried out in zinc alloy die casting pretreatment to a certain extent. Copper cyanide plating solution can even be plated to the surface of the substrate with very small shrinkage and intergranular gap. Compared with the cyanide free copper without sf-628, it does not contain strong chelating agent, so it is more likely to lead to the occurrence of poor zinc die casting connection. In addition, we should strengthen collaborative efforts and consider from the following aspects in combination with domestic successful experience:

1. The development and applicability of zinc die casting substrate coating: This includes the use of qualified high-quality alloy zinc and aluminum castings, advanced mold manufacturing and casting technology, reliable grinding and polishing process, etc. the surface is compact and high-quality workpieces can be machined effectively.

2. Adopting effective pre plating activation process: zinc alloy casting is selected to be smooth and efficient chemical electrolytic degreasing to large-scale production process. The application of anode electrolytic degreasing can effectively eliminate the aforementioned cathodic electrolytic degreasing caused by hydrogen gas caused by bubbles in zinc die casting coating. Secondly, proper anode electrolytic degreasing has excellent ability to remove scale and ash on the surface of parts, and also greatly improves the collaborative efforts of zinc coated surface on zinc castings.

3. Strict process control: sf-628 cyanide free alkaline copper plating is more sensitive to impurities, excessive accumulation of inorganic and organic impurities may lead to poor coating adhesion. Therefore, the control of reducing the volume of impurities entering and regular removal operation can not be ignored. In addition, electroplating process parameters should be adjusted to the best range regularly. 3、 Non cyanide alkaline copper plating process for zinc alloy die casting

1. Process:

Sf-6203 ultrasonic cleaning → sf-6203 ultrasonic cleaning → sf-630b ultrasonic cleaning → sf-6302 ultrasonic cleaning → sf-630b ultrasonic cleaning → sf-630b ultrasonic cleaning → cleaning → activation → cleaning → prepreg → sf-628 non cyanide copper plating → recovery → cleaning → other plating

Attention: three times of countercurrent flushing should be used when cleaning.

2. Process parameters

2.1 hot dip wax

Sf-6203 1-2% temperature 70-85 ℃ time: 3-5 minutes

The purpose of this method is to make the wax scale on the surface of the alloy moist, expand and partially peel off by hot dipping.

2.2 ultrasonic dewaxing

Sf-6203 1% temperature 55-70 ℃ for 1-5 minutes

Ultrasonic dewaxing combined with mechanical up-down or rotary motion can accelerate the stripping of wax scale. The effective capacity of ultrasonic unit is 8-10W / L.

2.3 ultrasonic degreasing

Sf-6302 1.5-3% temperature 50-70 ℃ 1-3 minutes

Moreover, for the wax scale on the surface of zinc die casting, the workpiece vibration with oil film surface hardness of 20kHz / min, and the oil removal effect of complex deep hole is more ideal.

2.4 anode electrolytic degreasing

Sf-303bi 5-7% temperature 50-70 ℃

The anode current density is 2-3a / DM2, and the time is 5-10S. Stainless steel plate is used to effectively remove the floating dust film on the workpiece surface.

2.5 activation (etching)

Sf-6505 2-4% at room temperature for 10-30 seconds

The effective activation of the workpiece surface will not cause obvious metal surface corrosion and light loss.

2.6 pre impregnation

Sf-628e 1-2% temperature room temperature time 10-30 seconds

The first step is to speed up the electrochemical reaction speed of the workpiece entering the bath, activate the surface of the workpiece, and improve the uniformity of the coating. At the same time, it can avoid impurity ions from entering the cyanide free copper barrel and polluting liquid after the first two washings.

2.7 sf-628 cyanide free alkaline copper plating

Sf-628cu 250-300ml / L metal copper 4.5-5.4g/l

SF-628E 100-120ml / l SF-628P 100-120ml / l

PH 9.2-9.8 temperature 50-55 ℃

Anode current density 2-3a / DM2 time ≥ 10 minutes

Stir with strong oil-free air

Filtration must be continuous without sulfur activated carbon

For cyanide free anode copper plating or non cyanide alkaline copper plating on 304316 stainless steel, the content of metal copper should be controlled to 4.5-5.4g/l. If the content is too high, it can be solved by reducing copper anode and adding insoluble anode. If the content is too low, the area of anode copper should be increased; if the content is too low, it should be added with high current impact plating for 0.5-1 min; The dosage of sf-628e is determined through the regular hull tank test to maintain the best coating coverage and ensure the coating has the best physical properties; coating performance, joint efforts to influence factors such as cyanide, iron, zinc and other impurities, one day later, electrolysis with corrugated plate for several hours, continuous filtration with activated carbon and conventional hydrogen peroxide treatment to effectively remove the above-mentioned impurities.

The subsequent coating is recommended to use zinc alloy, which is more gentle and can survive bright copper pyrophosphate in a good place. Especially for complex parts, it is more conducive to improve the plating rate and reduce the possibility of foaming.

Common faults and treatment of 2.8sf-628 cyanide free copper

fault

reason

countermeasure

The color of the coating is dark red or the coating is black, and the knot does not work well

1. Poor pretreatment, organic impurities enter

2. Cyanide effect

Hydrogen peroxide and activated carbon treatment

2. Hydrogen peroxide treatment and electrolysis

The coating in low current area is thin and the junction is not good

1. Lack of sf-628e

PH too low

High copper content

1. Add 10-20ml / lsf-628e into hull tank to measure joint force

2. Add sf-628p to pH 9.8

Anode graphite plate or stainless steel plate

Black sponge coating was found in high current area, but poor coverage in low current area

Iron impurity

High current electrolysis

2. Discard the iron parts in time so as to fish out

Coking in high current region

1. The current density is too high

2. Insufficient air mixing

Low bath temperature

4. The content of copper is less than 4G / L

1. Reduce cathode current density

2. Keep strong air stirring

3. Heat to 50-60 ℃

4. Adding sf-628cu can increase the content of copper to 7.5g/l

Zinc alloy after die casting copper foil from skin

The impurity content of silver and zinc is too high

Replace silver plated anode to remove electrolytic zinc with low current density

4、 Adhesion test of zinc alloy die casting coating

For sf-628 non cyanide alkaline copper parts, the following two test methods can be adopted for collaborative efforts:

A. Thermal shock test: put the workpiece in 150 ℃ oven for 1-1.5 hours, and immediately put it into 18-30 ℃ cold water, and the surface shall be free of blistering.

B. Natural materials that have been stored indoors for more than two months should have no blistering or peeling off.

5、 Production application and conclusion

In Zhuhai, zinc alloy electroplating products need copper, nickel and chromium products. The electroplating area is 16 DM2, foreign products need 150 ℃ cold and hot cycle test without foaming. We use this process to make foreign qualified products in 3000lsf-628 cyanide free alkaline copper electroplating solution, and the products adopt nickel nickel electroplating, and the overall appearance brightness is better than that of copper cyanide as the bottom product.

The production application shows that sf-628 cyanide free alkaline copper plating can obtain the appearance and synergistic effect of copper layer in zinc mold by using the above process, which also accumulates useful experience for its promotion in large area in the future.