There are these changes in the mass size of aluminum alloy before and after oxidation!?

Many people have a question: "Why do pores get bigger after oxidation?" This should be explained from the principle of oxidation, oxidation is different from spraying or electroplating, anodizing is carried out on the surface of aluminum alloy, it is a process of reaction from the surface to generate an oxide film.

In general, the growth process of oxide film includes the following two aspects: (1) the formation process of the film (2) the electrochemical dissolution process of the film

At the moment of electricity, oxygen and aluminum have a great affinity, and the aluminum substrate quickly forms a dense non-porous barrier layer, whose thickness depends on the tank voltage.

Due to the large volume of alumina atoms, it expands, the barrier layer becomes uneven, resulting in uneven current distribution, small resistance in the concave, large current, and the opposite of the convex.

Electrochemical dissolution and chemical dissolution of H2SO4 occur in the cavity under the action of electric field, and the cavity gradually becomes a hole and a hole wall, and the barrier layer is transferred to the porous layer.

The metal or alloy is used as the anode, and the oxide film is formed on its surface by electrolysis. The metal oxide film changes the surface state and performance, such as surface coloring, improving corrosion resistance, enhancing wear resistance and hardness, protecting the metal surface. Aluminum anodizing, aluminum and its alloy is placed in the corresponding electrolyte (such as sulfuric acid, chromic acid, oxalic acid, etc.) as the anode, under specific conditions and impressed current, electrolysis. The anodic aluminum or its alloy is oxidized to form a thin layer of aluminum oxide on the surface, with a thickness of 5 to 30 microns, and the hard anodic oxide film can reach 25 to 150 microns.

Early anodizing work

In the process of forming oxide film, it is necessary to do alkali etching and polishing work in the early stage.

Alkali corrosion is the process of eliminating and leveling the natural oxide film (AL2O3) on the surface of aluminum. The speed of alkali corrosion depends on the concentration and temperature of the alkali bath, which strongly depends on the dose of alkali corrosion agent (sodium gluconate) and the content of aluminum ions (AL3+). Aluminum surface quality, feel, flatness and oxide film electroplating, alkali corrosion all play a decisive role.

The purpose of alkali etching is to remove the oxidized film formed on the surface of aluminum parts by hot working or under natural conditions, as well as the residual oil applied during the production of milk and manufacturing molding. Whether this work is done thoroughly determines the key to the quality of the anodic oxide film obtained. The key points to pay attention to are the following. Carefully do a good job of inspection before alkali corrosion, found that not suitable for alkali corrosion treatment should be picked out in advance. The pretreatment method before alkali etching should be appropriate and thorough. Master the technological conditions of alkali etching operation correctly.

It is carried out on the polishing machine, the aluminum profile is placed on the work table regularly, and the surface is touched and rubbed by the high-speed rotating polishing wheel, so that the surface is smooth and flat, and even the mirror effect is achieved. Polishing is often used in production to eliminate extrusion streaks, so it is also called "mechanical sweep" at this time.

sum up

The change of aluminum alloy size can be selected, depending on the oxidation method, time, and pre-treatment process.

Smaller size: During the entire oxidation process, it is also necessary to soak the aluminum alloy in the sulfuric acid solution, this series of operations will cause corrosion of the aluminum alloy, so when we see the aluminum alloy product again, its size will become smaller due to corrosion.

Larger size: To do hard oxidation, you can make the overall size of the aluminum alloy has a greater increase.

The quality of aluminum alloy often shows a more obvious increase.