Art » The method of dehydrogenation after electroplating processing

Hydrogen embrittlement is a delayed fracture that occurs when hydrogen penetrates into the interior of the metal, causing the metal material to undergo a static stress below the yield strength of the material.

Hydrogen embrittlement is a relatively common phenomenon in engineering. Especially in the electroplating process, it is easy to cause hydrogen embrittlement of metal materials. Hydrogen embrittlement in electroplating process mainly occurs in pickling, electroplating and other processes.

Therefore, many parts are subjected to dehydrogenation treatment after electroplating, to avoid the hazard caused by hydrogen embrittlement. The following is a small series to introduce the method of removing hydrogen.

1 general dehydrogenation method

(1) Place the parts to be dehydrogenated in an oven (preferably in a vacuum furnace), or in hot oil (for hard chrome-plated parts), at 3 to 200 °C for more than 3H.

(2) The removal of hydrogen from the hot oil can have the same effect as the removal of hydrogen in the oven. Because of its uniform heating, the coating also has the function of filling the pores, which is beneficial to improve the protective function of the coating, and the requirements for the equipment are also simple.

2 According to the requirements of the workpiece, the method of removing hydrogen

For example, hard chrome plating, when the hard chrome plating is too low, only 13%~18%, most of the current is consumed in the precipitation of hydrogen, hydrogen easily diffuses into the crystal lattice of the plating layer and the base metal, and the hydrogen permeation is serious. Therefore, the fatigue strength is reduced, and the dynamic and static load strength is affected. Therefore, the requirement of dehydrogenation after chrome plating should be proposed in the design. After the dehydrogenation treatment, 60% to 70% of hydrogen infiltrated into the plating layer and the matrix can be removed, thereby greatly reducing the brittleness without lowering the hardness.

3 hot oil instead of dehydrogenation in the oven

The current efficiency of chrome plating is very low, so the plating porosity is high, and the coating is very easy to passivate. At the same time, due to the advantage of the chromium layer on the surface of the steel part, the cathode coating is very easy to cause rust when the thickness of the coating is thin. In order to improve this defect, hot oil can be used to remove hydrogen in the oven under the same process conditions. Practice has proved that the process can not only maintain the temperature uniformity of various parts of the workpiece, but also achieve a complete hydrogen removal effect, and can effectively consider the pores and cracks of the chromium layer to fill the grease, thereby improving the protection ability of the chromium layer.

4 dehydrogenation temperature can not be too high

For example, after galvanizing , in addition to hydrogen, hydrogen is removed from the metal by heating. The effect of hydrogen removal is related to the temperature of hydrogen removal and the length of holding time. The higher the temperature of hydrogen removal, the longer the time, the more complete the removal of hydrogen. But not more than 250 degrees Celsius. Because the crystal structure of the galvanized layer is deformed, brittle, and the corrosion resistance is lowered at this temperature.

In addition to hydrogen, you should also pay attention to the following points:

(1) Safety factor for the use of parts. For parts of high safety importance, the dehydrogenation time should be extended appropriately.

(2) The geometry and cross-sectional area of ​​the part. Small, thin parts such as notches that are prone to stress concentration, small angles, etc. should be enhanced to remove hydrogen.

(3) The degree of hydrogen permeation of the part. In the surface treatment, parts with more hydrogen and longer treatment time should be strengthened.

(4) The nature of the force in the use of the part. When the part is subjected to high tensile stress, the dehydrogenation should be strengthened, and hydrogen embrittlement will not occur only under compressive stress.

(5) The surface of the coating must be kept clean before hydrogen removal. The hydrogen removal should be treated before passivation to ensure the hydrogen removal effect and the quality of the passivation layer.

(6) In addition to hydrogen, it should be guaranteed that the time is continuous and cannot be stopped in the middle. Whenever the oven is lowered to room temperature, open the oven and remove the parts.

(7) Try not to rework after the parts are plated. If it is necessary to plate, the coating can be removed with an alkaline solution and the hydrogen removal time can be extended after plating.

(8) The dehydrogenation treatment should be carried out within 3 hours after electroplating.