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General Principle Of Cnc Machined Anodized Aluminum Parts

Molto Precise Machining Co.,Ltd | Updated: Dec 01, 2018

General principle of cnc machined anodized aluminum parts

1. General principle of oxide film formation on anodized aluminum oxide plate:
The process of forming an aluminum oxide film on the surface by electrolysis using an aluminum plate as an anode in an electrolyte solution is called anodizing treatment of an aluminum plate. The cathode in the device is a material having high chemical stability in an electrolytic solution, such as lead, stainless steel, aluminum, and the like. The principle of aluminum anodization is essentially the principle of water electrolysis. When the current is passed, hydrogen is evolved on the cathode; on the anode, the evolved oxygen is not only molecular oxygen, but also atomic oxygen (O) and ionic oxygen, usually expressed as molecular oxygen in the reaction. The aluminum as the anode is oxidized by the oxygen deposited thereon to form a water-free aluminum oxide film, and not all of the generated oxygen acts on the aluminum, and a part thereof is precipitated in a gaseous state.
2. Selection of oxidized electrolytic solution of anodized aluminum plate:
A prerequisite for the growth of the anodized film is that the electrolyte should have a dissolution effect on the oxide film. However, this does not mean that anodization can form an oxide film or the resulting oxide film has the same properties in all electrolytes in which dissolution is present.
3. Types of oxidation of anodized aluminum oxide sheets:
Anodizing is divided into current forms: direct current anodization, alternating current anodization, and pulse current anodization. According to the electrolyte, there are natural anodic oxidation of sulfuric acid, oxalic acid, chromic acid, mixed acid and sulfoorganic acid as the main solution. According to the film layer, there are anodization of a common film, a hard film (thick film), a porcelain film, a bright modification layer, and a barrier layer for semiconductor action. The common anodizing methods and process conditions for aluminum and aluminum alloys are shown in Table-5. Among them, the application of direct current sulfuric acid anodization is most common.
4. Structure and properties of anodized aluminum oxide film:
The anodized film is composed of two layers, and the porous thick outer layer is grown on a dense inner layer having dielectric properties, and the latter is called a barrier layer (also called an active layer). Observation by electron microscopy revealed that the longitudinal and lateral faces of the film layer almost all showed tubular holes perpendicular to the metal surface, which penetrated the outer layer of the film up to the barrier layer between the oxide film and the metal interface. The porous alumina is surrounded by dense alumina to form a honeycomb hexagonal body called a unit cell, and the entire film layer is composed of a myriad of such unit cells. The barrier layer is composed of anhydrous aluminum oxide, which is thin and dense, has a high hardness and prevents the passage of electric current. The barrier layer has a thickness of about 0.03-0.05 μm, which is 0.5% to 2.0% after the total film. The porous outer layer of the oxide film is mainly composed of amorphous alumina and a small amount of hydrated alumina, and further contains a cation of the electrolyte. When the electrolyte is sulfuric acid, the sulfate content in the film layer is normally 13%-17%. Most of the excellent properties of the oxide film are determined by the thickness and porosity of the porous outer layer, and they are all closely related to the anodizing condition.

CNC Machined Anodized Aluminum Parts

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