CN1654703A - Surface treatment method - Google Patents

Abstract

The surface treatment process for magnesium alloy casing includes the pre-treatment of magnesium alloy casing base and metal target, forming a metal coating on the surface of the magnesium alloy casing base with the metal target, and heat treatment of the magnesium alloy casing base with the surface coating for diffusion to form intermetallic compound with high antiwear performance and heat resistance and to improve the surface performance of magnesium alloy casing.

Description

Surface treatment method

【Technical field】

The invention relates to a surface treatment method, in particular to a surface treatment method of a magnesium alloy casing applied to portable electronic devices such as notebook computers or mobile phones.

【Background technique】

In recent years, with the rapid development of the application of magnesium alloys in portable electronic products such as notebook computers, it has met people’s requirements for portable electronic products in terms of lightness, shortness and EMI. Corrosion is easy to occur in the atmosphere, and at the same time, it has the characteristics of poor wear resistance, so they must be surface treated to increase wear resistance and corrosion resistance.

At present, the surface treatment of magnesium alloy mainly includes chemical film-forming treatment, anodic oxidation treatment and metal coating treatment. However, it is difficult for magnesium alloys treated with hexavalent chromium chemical film formation to meet the requirements of magnesium alloy products in terms of corrosion resistance and scratch resistance, and the country is gradually restricting chromization treatment for the pollution problems in the processing process. However, the chromium-free chemical film-forming treatment has the disadvantages of insufficient density of the film layer and poor protective performance of the film; the porosity of the anodized film brings difficulties in improving the protective performance of the film. Although the micro-arc oxidation method can locally melt and reduce the pores, the It is difficult to completely eliminate, and the investment in micro-arc oxidation treatment equipment is large; and there are pores in the coating treated by metal coating. In order to prevent the coating pores from extending directly to the magnesium alloy substrate, a thicker coating must be obtained through multi-layer metal plating, but The processing process is more complicated.

Since intermetallic compounds have superior properties of compact structure, wear resistance and corrosion resistance compared with metal coatings, it has become an option to improve the surface properties of magnesium alloy shells through intermetallic compound films. Generally, when making an intermetallic compound film, it is necessary to prepare the required intermetallic compound first, and then produce a layer of intermetallic compound film. In this way, there is only one kind of film composition. However, for intermetallic compounds with different ratios, the target must be replaced, which limits the application range and increases the cost. At the same time, the obtained intermetallic compound forms a thin film and deposits on the magnesium alloy shell by evaporation or sputtering. The formed film and the magnesium alloy shell substrate cannot achieve metal bond connection. The possibility of peeling off will weaken the protective effect of the intermetallic compound film on the magnesium alloy shell substrate.

【Content of invention】

The purpose of the present invention is to provide a surface treatment method for a magnesium alloy shell, which can not only improve the surface performance of the magnesium alloy shell base material, but also be widely used and the cost is not high.

The object of the present invention is achieved through the following technical solutions: providing a magnesium alloy shell base material and a metal target material; performing surface pretreatment on the magnesium alloy shell base material and the metal target material before surface treatment; utilizing the metal target material to steam Plating or sputtering the base material of the magnesium alloy shell to form a metal coating on the surface of the base material of the magnesium alloy shell; performing heat treatment on the base material of the magnesium alloy shell and the coating on the surface to cause a diffusion reaction to form an intermetallic compound.

Compared with the prior art, the present invention forms a metal coating layer on the surface of the magnesium alloy shell base material by first evaporating or sputtering the target metal, and then heats and diffuses to form an intermetallic compound film layer, which is beneficial to the freedom of producers. Selecting different metals to form an intermetallic compound film layer on the surface of the magnesium alloy shell base material makes the metal selection range of the intermetallic compound film more extensive, and at the same time avoids long-distance transportation for purchasing special intermetallic compounds. It can reduce the production cost; in addition, the formed intermetallic compound film layer is obtained by the diffusion reaction of the metal coating, and the intermetallic compound film layer and the magnesium alloy shell substrate are connected by metal bonds and are not easy to peel off, which can improve the magnesium alloy shell. Body substrate surface properties.

【Detailed ways】

The magnesium alloy shell surface treatment method provided by the present invention carries out the process as follows:

Firstly, a magnesium alloy shell base material and a metal target material are provided.

Provide a magnesium alloy shell substrate, and provide a metal target that can form a metal coating on the surface of the magnesium alloy shell substrate by evaporation or sputtering. The metal target can be nickel, iron, molybdenum and other metals , the target material of this embodiment is nickel metal, and the metal target material can be made into various shapes, and the special design of the machine can be used for better control and the most efficient production. The thickness of the target material of the present invention can be 5-15mm. It is better to be 10mm thick.

Second, surface pretreatment is carried out on the magnesium alloy shell base material and the metal target.

The main steps of the surface pretreatment of the magnesium alloy shell base material are: degreasing and cleaning first, followed by two water washings, then pickling and water washing, then film formation treatment, and finally water washing, pure water washing and drying. The specific process is as follows: firstly, the magnesium alloy shell base material is pre-washed, and the oil stain on the surface of the magnesium alloy shell base material is removed with a strong corrosive acid solvent, and the oil stain and the magnesium alloy shell base material are destroyed in a large area. The bonding of the magnesium alloy shell base material is then carried out to the main stripping and cleaning, and the oil stain on the surface of the magnesium alloy shell base material is removed with a mild solution, but the surface of the magnesium alloy shell base material itself must not be damaged. Next, wash with water twice in sequence to thoroughly wash off the degreasing solvent and pollution remaining on the surface of the magnesium alloy shell base material. Further wash the magnesium alloy shell base material with an acid solution to adjust the activation of the surface of the magnesium alloy shell base material, neutralize the properties of the residual solution on the surface, and at the same time improve the adhesion performance of the film layer generated in the subsequent process, and then carry out the third Washing with water to wash away the residual acid and pollutants on the surface of the magnesium alloy shell base material, and at the same time apply a magnesium alloy surface treatment agent to the surface of the magnesium alloy shell base material for chromium-free chemical film-forming treatment, and in order to ensure the The temperature is constant, and a circulating cooling system is required to form a film forming process to form a corrosion-resistant film layer and improve the adhesion of the subsequent coating layer. Residual solvents and dirt on the surface are removed, followed by a fifth wash with pure water to remove the remaining electrolyte on the surface of the magnesium alloy shell base material or soluble salts by soaking, and finally dry the base material, waiting for the subsequent process.

If the surface is treated by sputtering, pre-sputter the metal target before the first plating to remove the oxide layer or contamination layer on the surface of the metal target.

Thirdly, the base material of the magnesium alloy shell is evaporated or sputtered with a metal target, and a metal layer is plated on the surface of the base material of the magnesium alloy shell.

Vacuum evaporation can be used for evaporation, and DC dipole sputtering and magnetron sputtering can be used for sputtering. For example, the process flow of DC dipole sputtering coating treatment is as follows: firstly, pre-plating treatment is performed, and then the magnesium alloy shell base is clamped. materials and metal targets, followed by vacuuming and baking, bombardment treatment, sputtering deposition treatment, and finally cooling, pick-up and post-processing. The specific process is: first place the nickel metal target and the magnesium alloy shell substrate together in the sputtering chamber, vacuumize the sputtering chamber to about 4×10 ^-1 Pa, then fill it with argon, and During the sputtering process, the vacuum degree is controlled at 1-10Pa, the target cooling water and the DC power supply are connected, a DC high voltage of 1-5Kv is applied, and the timing is started. After 3 hours, the power supply is cut off, and the argon gas charging valve is closed to complete the sputtering process. Plating, so as to form a thin dense nickel metal coating on the base material of the magnesium alloy shell, and the thickness of the coating is 10-20um. Roasting and bombardment can be regarded as unnecessary processes.

Fourth, heat-treat the magnesium alloy shell base material and its surface metal coating, so that the metal layer will undergo a diffusion reaction with the magnesium alloy shell base material during the treatment process, forming a stable phase at this temperature, that is, the required intermetallic compound.

Place the magnesium alloy shell base material and its surface metal coating in a high-vacuum heating furnace, apply a heating temperature of 300°C to 400°C, preferably 350°C, and continue heating for 20 to 30 hours, preferably 24 hours, so that The nickel metal coating fully diffuses on the surface of the magnesium alloy housing base material and reacts to form a corresponding Mg2Ni intermetallic compound film layer, which is then cooled in a vacuum environment.

Fifth, surface coating treatment is carried out on the magnesium alloy shell after surface treatment, so as to further strengthen the protection of the surface of the magnesium alloy shell base material and beautify the appearance of the shell.

Compared with the prior art, the surface treatment method of the magnesium alloy shell base material of the present invention has the following advantages: first, a metal layer is formed on the surface of the magnesium alloy shell base material by sputtering, compared with directly plating on the base material surface The method of intermetallic compounds, the selection of metal targets is more free and extensive, avoiding the limitation of the types of magnesium intermetallic compound targets, and at the same time, it also avoids long-distance transportation for purchasing special intermetallic compounds. It can reduce the production cost; the intermetallic compound film layer formed by connecting the magnesium alloy shell base material and the metal coating with metal bonds is more difficult to peel off the magnesium alloy shell base material than the combination method in which the metal coating layer is deposited on the surface of the base material, and has Stronger corrosion resistance and wear resistance can make the surface of magnesium alloy shell base material more stable protection.

Claims (5)

1. A surface treatment method, which can treat the surface of a magnesium alloy shell, the steps comprising: providing a magnesium alloy shell base material and a metal target material; performing surface pretreatment on the magnesium alloy shell base material and the metal target material Treatment; use metal targets to carry out metal coating treatment on the magnesium alloy shell base material, and form a metal coating layer on the surface of the magnesium alloy shell base material; heat treat the magnesium alloy shell base material and its surface coating to cause a diffusion reaction Intermetallic compounds are formed. 2. The surface treatment method for a magnesium alloy shell as claimed in claim 1, characterized in that: the metal target used can be nickel, iron, molybdenum and other metals. 3. The surface treatment method of the magnesium alloy shell according to claim 1, characterized in that: the metal coating treatment adopts the surface treatment method of evaporation or sputtering. 4. The surface treatment method for magnesium alloy shells according to claim 1, characterized in that: the diffusion reaction of the metal coating on the surface of the magnesium alloy shell base material occurs under heat treatment with controlled temperature and time, and generates intermetallic compounds. 5. The method for surface treatment of magnesium alloy casing according to claim 1, characterized in that: the heat treatment of the metal coating and the base material of the magnesium alloy casing is carried out in a high vacuum environment.