With the increasingly fierce market competition, many aluminum alloy die-casting enterprises have expanded their business to the international market since China joined the WTO. There are many requirements in the international market, such as delivery time, quality, appearance and packaging, and whether it belongs to the environmental protection series. Here we are talking about environmental protection. Now our country is also advocating green action. The world is also paying attention to environmental improvement.

Now, as a large number of gas, mocha and toner products, they are also constantly required to meet the environmental system requirements. As exported products, they must comply with the eu RoHS directive, and the ability of products to resist corrosion is also a key factor. This step is inevitable. Then, as an aluminum alloy product, how can we do this step? This is the need to carry out surface treatment on our aluminum alloy product, that is, passivation.

Passivation is to make the surface of the metal into a state which is not easy to be oxidized, and to slow the corrosion rate of the metal. An active metal or alloy in which chemical activity is greatly reduced and becomes a phenomenon of noble metal state, called passivation.

If the corrosion product of metal due to the action of medium has a dense structure and forms a thin film (often invisible), which is closely covered on the surface of the metal, it changes the surface state of the metal, making the electrode potential of the metal jump in the positive direction and become a dull state of corrosion resistance. For example, when Fe goes to Fe++, the standard potential is -0.44v, after passivation, it jumps to + 0.5-1v, and this film shows the performance of precious metal that is corrosion-resistant. This film is called passivation film. Passivation of metals can also be a spontaneous process (such as creating a layer of insoluble compounds on the surface of a metal, known as an oxide film). In industry, passivating agent is used to passivate the metal to form a protective film.

Metals are protected from corrosion by being passivated.

First of all, it should be clear whether the passivation is caused by the metal phase and the solution phase or by the interface phenomenon. The effect of mechanical scraping on metals in a passive state has been studied. Experiments have shown that when metal surface is polished continuously during measurement, the electric potential of the metal moves violently in the negative direction, that is, dressing the metal surface can cause the activation of the metal in the passive state. That is to say, passivation is an interfacial phenomenon. It is changed on the interface between metal and medium under certain conditions. Electrochemical passivation is when anode polarization occurs, metal potential changes and metal oxides or salts are formed on the electrode surface. These substances are closely covered on the metal surface as passivating film, which leads to metal passivating. Chemical passivating is caused by the direct action of oxidants such as concentrated HNO3 on the metal and the formation of oxide film on the surface, or the addition of easily passivating metals such as Cr, Ni, etc. In chemical passivation, the concentration of the oxidant added should not be less than a critical value, otherwise, it will not cause a blunt state, but will cause faster dissolution of the metal. In chemical passivation we now advocate green passivation -- trivalent chromate passivation solution.

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