Detailed explanation of the principle and selective application of chromium-free electrolytic polishing

[Al channel network] compared with chemical polishing, electrolytic polishing is even better, electrolytic polishing has the following advantages:

1, the equipment is simple, the process parameters are easy to control, can replace the mechanical polishing, or continue to mechanical polishing under certain special requirements after the chemical polishing or electrolytic polishing, the surface brightness is higher, and relative to the mechanical polishing easier to use automated scale produce;

2. It has a wide range of requirements for the structure and size of the profiles. It can handle industrial materials that are used for precision parts with high surface requirements, and have large or small external dimensions and shapes that cannot be processed with complex mechanical polishing.

3. After the electrolytic polishing, the surface of the aluminum profile is clearer and cleaner, without residual mechanical polishing dust, and has better corrosion resistance;

4. Electropolished surface mirror reflectivity is higher and the metal feel will be better.

Electropolishing is also referred to as electrochemical polishing. Aluminum is used as the anode to infiltrate the prepared electrolyte solution. Corrosion-resistant and microscopically protruding parts with good performance (such as stainless steel) are used as the cathode. According to the electrolysis tip discharge principle, After the power is applied, the micro-protrusions on the surface of the aluminum profile are preferentially dissolved. At the same time, the dissolved product and the electrolyte on the surface form a highly resistive viscous liquid film layer. The liquid film layer on the micro-projection site is thin and its resistance is small. The preferential dissolution is maintained, and the liquid film layer of the dome is thicker and the resistance increases. The dissolution rate is relatively slow. After a short period of electrolytic treatment, the protruding part is dissolved and leveled up to the position of the dome, making the surface of the aluminum rough. Decreases the degree of smooth light.

Selection and Application of Electroless Polishing without Chromium

1, a typical electrolytic polishing process

Electropolishing enables the aluminum surface to exhibit a high specular reflection performance in the light effect, and is suitable for aluminum materials with special bright surface quality requirements in the industrial and scientific fields. The typical electrolytic polishing process includes acidic electrolytic polishing and alkaline electrolytic polishing. The main types are as follows:

1 Sodium carbonate - trisodium phosphate alkaline electrolytic polishing process (Brytal process), this process is particularly suitable for polishing high purity aluminum, commonly used in aluminum products have been used for mechanical polishing and still need to further improve the brightness, the advantage is the use of current density Low, the polishing solution on the aluminum substrate dissolution rate is small, the disadvantage is that the solution is consumed faster, more sensitive to impurities.

2 Phosphoric acid-chromic acid-sulfuric acid electrolytic polishing method (Battle method), sulfuric acid can effectively reduce the current density and voltage of the polishing operation, and perform electrolytic polishing at a higher temperature in a certain range, and at the same time can also inhibit the occurrence of pitting corrosion. Chromic acid improves the specular reflectance of polished aluminum surfaces.

3 fluoroboric acid electrolytic polishing process, with borofluoric acid as the main component of the electrolyte, this process is more suitable for high purity aluminum, the reflectance can reach 85%.

4 The sulfuric acid-chromic acid electrolytic polishing process (Aluflex method) has a relatively simple bath control. The dissolution rate of aluminum in the polishing solution is quite fast at the initial 2 minutes and is about 25 μm. When the content of aluminum ions in the bath is too high, defects such as insufficient lightness or attachments on the surface may occur.

2, chromium-free electrolytic polishing process

As the traditional aluminum and aluminum alloy electrolysis polishing solution contains chromic acid, which is highly toxic, it seriously pollutes the environment and waste water is difficult to handle, which is not conducive to the normal implementation of clean production. For this reason, it is imperative to adopt a new type of polishing process that does not harm the environment to replace the typical electrolytic polishing process.

Summarizes the technological researches made by predecessors on chromium-free electrolytic polishing. Most of these polishing solutions use phosphoric acid as the main component. Alcohols are used instead of chromic acid as a corrosion inhibitor, resulting in the formation of hydrogen bonds between alcohol molecules. Cooperation uses this special property to achieve flattening. According to the electropolishing theory, an alcohol electrolysis polishing liquid having an association property forms a mucus layer on the surface of the polished aluminum material, so that the depression position is in a stable passivation state, and the convex protrusion is dissolved at a faster rate, obtaining Smooth and shiny surface. Increasing the number of hydroxyl groups of the alcohol molecule is beneficial to polishing, and the use of a soluble polyol polymer containing more hydroxyl groups is more effective.

The chromium-free electrolytic polishing process has the great advantage of no yellow smoke, no flow mark, high stability, high brightness and high efficiency.