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Aluminum oxide surface pretreatment

Release time:

2022-05-16 16:09

1. aluminum oxide surface pretreatment

No matter what method is used to process aluminum materials and products, there will be dirt and defects on the surface to varying degrees, such as dust, metal oxides (natural or high-temperature formed alumina film), residual oil stains, asphalt marks, manual handprints (mainly composed of fatty acids and nitrogen-containing compounds), welding flux, corrosion salts, metal burrs, slight scratches, etc. Therefore, before the oxidation treatment, the surface of the product is cleaned by chemical and physical methods to expose the pure metal substrate to facilitate the smooth oxidation and coloring, so as to obtain a solid combination with the substrate, the color and thickness meet the requirements and have good properties such as corrosion resistance, wear resistance and weather resistance.

(I) skim

Aluminum andAluminum alloySurface degreasing includes organic solvent degreasing, surfactant degreasing, alkaline solution degreasing, acidic solution degreasing, electrolytic degreasing, and emulsification degreasing. Among these methods, degreasing with an alkaline solution, particularly a hot sodium hydroxide solution, is effective.

(II) alkali inhibitor

Alkaline etching is a process in which the surface of aluminum products is cleaned in a sodium hydroxide solution with or without the addition of other substances. It is also commonly referred to as alkali corrosion or alkali washing. Its function is as a supplementary treatment for products after degreasing by some degreasing methods, so as to further clean up the oil dirt attached to the surface, and remove the natural oxide film and slight scratches on the surface of the products. Therefore, the product is exposed to a pure metal substrate, which is beneficial to the generation of the anode film and obtains a higher quality film layer. In addition, by changing the composition of the solution, the temperature, the treatment time and other operating conditions, it is possible to obtain a smooth or satin matt or glossy surface in different states. The basic composition of the washing solution is sodium hydroxide, and a regulator (NaF, sodium nitrate), fouling agent, (gluconate, heptanoate, tartrate, gum arabic, dextrin, etc.), sequestering agent (polyphosphate), detergent.

(III) neutralization and water cleaning

The gray or black hanging ash attached to the surface of aluminum products after etching and washing is not dissolved in cold or hot water washing, but it can be dissolved in acidic solution. Therefore, products etched and washed with hot alkali solution must be subjected to acid leaching cleaning aimed at removing hanging ash and residual alkali solution to expose bright basic metal surfaces. This process is called neutralization, luster or light extraction treatment. Its process is the product in.300-400g/LNitric acid (1420kg/cubic meters) solution, room temperature leaching, leaching time varies with the composition of the metal, general leaching time3-5Minutes. Hanging ash on aluminum alloy products containing silicon or manganese, available nitric acid and hydrofluoric acid volume ratio.3:1The mixture is treated at room temperature.5-15Seconds. Neutralization treatment can also be carried out in nitric acid-containing300-400g/Land chromium oxide5-15g/Lsolution or chromium oxide100g/LAdd sulfuric acid (1840kg/cubic meters)10ml/LThe solution is carried out at room temperature. The purpose of water cleaning between each process is to remove the residual liquid and water-soluble reaction products on the surface of the product, so that the next process bath is not contaminated and the treatment efficiency and quality are ensured. Cleaning mostly uses a cold water cleaning. However, the products after alkali etching generally use hot water followed by cold water double cleaning. The temperature of the hot water is40-60Degree. After the treatment of the products can be oxidized by water cleaning, so this cleaning should be particularly careful to prevent the clean surface from being contaminated. Otherwise, the effective treatment of the first few procedures may be due to improper cleaning and the previous efforts. The products after neutralization and water cleaning should be oxidized with the upper. Stay in the air should not be too long, such as stay30-40Minutes, the product needs to be re-etched and neutralized.