Many people believe that the main problem of aluminum alloy electroplating is the adhesion of the coating. Especially the aluminum alloy electroplated parts produced are of various types and complex structures. The problems are prominently reflected in the inner cavity, groove and back of the aluminum casting. , Blind holes and screw holes, etc.
In summary, the adhesion problem of aluminum alloy electroplating pretreatment is mainly caused by the following reasons:
(1) The inner cavity diameter of the aluminum alloy electroplated parts is too small and too deep, so that the plating solution and the cleaning solution flow and circulate in the workpiece less, so the pretreatment work around the inner hole groove of the product is not thorough. Therefore, the adhesion of the coating is poor or there is no adhesion; but there is interfacial tension at the root and right angles of the product, which makes it impossible to clean it. At this time, the obtained coating cannot guarantee good adhesion.
(2) In the pre-treatment process, due to the etching effect of acid and alkali solutions, especially the rough and porous oil surface, it is not easy to clean thoroughly. In the later stage of electroplating, the solution in the cracks and the surface of the micropores will definitely be spit out. Affect the quality of deep deposits.
2. Improved plan for the pre-treatment part of targeted aluminum alloy electroplating
According to repeated experiments on the aluminum alloy electroplating process, it is found that the angles and cracks of the electroplated surface can be effectively treated in the acid-base solution, but why the problem repeatedly occurs? This is mainly due to the pre-treatment of the aluminum alloy electroplating process It is caused by incomplete cleaning of the rough surface, included angle, and gap of the electroplated parts during water cleaning.
In order to solve the problems in the conventional pretreatment cleaning of aluminum alloy electroplating, we repeatedly tested a variety of water cleaning methods. Finally, we concluded that under the conditions of ensuring the quality of the coating and cost-effective Before dipping galvanizing, add an ultrasonic oscillating water cleaning, and the more advanced aluminum alloy electroplating process:
Alkali etching-washing-acid washing-water washing-ultrasonic cleaning-once dipping zinc-washing-acid washing-water washing-ultrasonic cleaning-dipping zinc twice.
3, process improvement
3.1 Improvement of water cleaning method during aluminum alloy electroplating
3.2 Introduce ultrasonic cleaning to aluminum alloy electroplating production application.
We know that due to the strong penetrating ability of ultrasound, it has a good cleaning effect on workpieces with complex shapes, cavities and fine holes, which is unmatched by other cleaning methods.
(1) The principle of ultrasonic cleaning is used in aluminum alloy plating.
The basic principle of ultrasonic cleaning is the "cavitation" effect. In the process of ultrasonic "cavitation" effect, an instantaneous high-pressure shock wave exceeding 100 MPa is formed, which produces intense stirring effect on the medium solution. The "cavitation" effect continues near the interface between the surface of the workpiece and the cleaning fluid, knocking down the dirt adhering to the surface of the workpiece.
(2) Ultrasonic equipment selection and parameter design in aluminum alloy electroplating production.
① Ultrasonic equipment. In recent years, domestic companies specializing in the production of ultrasonic equipment have continued to emerge, and a variety of ultrasonic cleaning machines specifically used in the field of surface treatment have been on the market. Some companies are carrying out technical transformation on the existing aluminum alloy automatic silver plating line, adding an ultrasonic cleaning tank before the primary and secondary zinc dip tanks, the tank size is 1500mm×1000mm×1000mm, and the tank body is made of PP material. According to the structure of the silver-plated wire tank, the vibration box type ultrasonic is adopted, and the material of the ultrasonic vibration box is adopted.
is made of 316I stainless steel plate, which is formed by argon arc welding. The ultrasonic vibration box is installed on the side of the cleaning tank, and the tank body is lined with 316L stainless steel, which can effectively reduce the absorption of ultrasonic energy by the PP material. The transmitting surface of the ultrasonic vibration box is treated with hard chrome plating, which can enhance the service life of the ultrasonic vibration box.
②Ultrasonic power. The higher the ultrasonic power, the stronger the cavitation effect, the better the cleaning effect, and the faster the speed. However, for workpieces with high machining accuracy, low surface roughness and loose workpiece materials, such as long-term strong washing will cause damage to the surface condition or even scrap, so the cleaning power should be based on the geometric shape of the workpiece, the size accuracy requirements and the reasonable material of the workpiece select. Most of the workpieces of a company are aluminum alloy forging blanks with low surface roughness, and there are also some aluminum alloy castings with loose materials. While ensuring the cleaning quality, after calculation and analysis, for a cleaning tank with a length of 1500 × a width of 1000 × a height of 1000 mm, each tank requires 12 ultrasonic vibrators, and the total power of the vibrators is 1296w.
③Ultrasonic frequency. The lower the ultrasonic frequency, the greater the cavitation phenomenon, and the stronger the effect. However, due to the corresponding longer wavelength, the directionality of the impact force is weakened, and the cleaning effect of the part of the surface covered by the workpiece will be affected. However, the gap or the small hole of the workpiece will be deep. The dirt can be removed, so when selecting the ultrasonic frequency range, it should be differentiated according to the shape and structure of the workpiece. Generally, a higher frequency should be used for small workpieces, and a lower frequency should be used for large workpieces. In the electroplating pretreatment process, the commonly used frequency is between 15-40kHz.
4. Verification of the effect of improved aluminum alloy plating pretreatment
Before the improvement of the aluminum alloy electroplating process, the roots and slits of the inner cavity of the workpiece were tested with PH test paper before the workpiece was immersed in zinc. The roots and slits of the workpiece were obviously red. This is because the acid at the corners of the workpiece processing surface was not cleaned. It shows that the pre-processing is not thorough. After adding ultrasonic cleaning to the aluminum alloy electroplating process, PH test paper is used to test that the corners of the workpiece surface are not discolored. This intuitive reflection says that the cleaning effect is greatly improved.
5. Summary of pre-processing for aluminum alloy electroplating processing
Our long-term practice in electroplating production has proved that there are more quality problems in aluminum alloy electroplating than ordinary hardware, but we only need to grasp the core key of various problems in the production process, and carefully observe and diligently during the electroplating process. After thinking, summarizing, and effectively combining and improving these findings, the quality and stability of aluminum alloy electroplated parts can be successfully maintained.