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2022.6.11
When it comes to high-volume manufacturing, zinc alloy die casting is one of the most effective and adaptable technologies. Surface treatment is to form a surface layer with some or more special properties on the surface of zinc alloy die castings by physical or chemical methods. The surface treatment can improve the product’s appearance, texture, function, and other aspects of performance. We are going to talk about what surface treatment can zinc alloy die castings do and list each of their advantages and disadvantages.
1. Anodic oxidation
It is mainly the anodizing of aluminum alloy die castings. For technical reasons, zinc alloy die castings cannot be made for the time being. A layer of Al2O3 (alumina) film is formed on the surface of aluminum alloy die castings by using the electrochemical principle. This layer of oxide film has special characteristics such as protection, decoration, insulation and wear resistance.
Monochrome, gradient:
Polishing / sandblasting / wire drawing → degreasing → anoxic oxidation → neutralization → dyeing → hole sealing → drying
Two color:
① Polishing / sandblasting / wire drawing → degreasing → masking → anodizing 1 → anodizing 2 → hole sealing → drying
② Polishing / sandblasting / wire drawing → degreasing → anodizing 1 → radium carving → anodizing 2 → hole sealing → drying
Technical features:
1. Lifting strength
2. Achieve any color except white
3. Realize nickel free hole sealing and meet the nickel free requirements of Europe, the United States and other countries
Technical difficulties and key points for improvement:
The yield level of anoxic oxidation is related to the cost of the final product. The key to improve the yield lies in the appropriate amount of oxidant, temperature and current density, which requires the aluminum alloy die casting plant to constantly explore and seek breakthroughs in the production process.
2. Electrophoresis
It is used for stainless steel, aluminum alloy die castings, zinc alloy die castings, etc. it can make products show various colors, maintain metal luster, enhance surface performance and have good corrosion resistance.
Technological process:
Pretreatment → electrophoresis → drying
Advantage:
1. Rich colors;
2. No metal texture, can cooperate with sand blasting, polishing, wire drawing, etc;
3. Processing in liquid environment can realize the surface treatment of complex structure;
4. The process is mature and can be mass-produced.
Disadvantages:
The ability to cover up defects is general, and the pretreatment requirements for electrophoresis of die castings are high.
3. Micro arc oxidation
The process of applying high voltage in electrolyte solution (generally weak alkaline solution) to form ceramic surface facial mask layer is the result of the synergistic effect of physical discharge and electrochemical oxidation.
Technological process:
Pretreatment → hot water washing → Mao → drying
Advantage:
1. Ceramic texture, dull appearance, no high gloss products, delicate feel, anti fingerprint;
2. A wide range of substrates: Al, Ti, Zn, Zr, Mg, Nb, and their alloys;
3. Simple pretreatment, excellent corrosion resistance, weather resistance and heat dissipation performance.
Disadvantages:
At present, the color is limited, only black and gray are mature, and bright colors are difficult to achieve at present; The cost is mainly affected by the high consumption of film, which is one of the highest costs in surface treatment.
4. PVD vacuum plating
The full name of physical vapor deposition is an industrial manufacturing process, which mainly uses physical processes to deposit thin films. Vacuum electroplating process can be used for various zinc alloy die castings and aluminum alloy die castings.
Technological process:
Pre PVD cleaning → furnace vacuumizing → target washing and ion cleaning → coating → coating completion, cooling out → post-treatment (polishing, AFP)
Technical features:
PVD (physical vapor deposition) can be used to coat metal surfaces with metal-ceramic decorative coatings with high hardness and wear resistance
5. Electroplating
It is a technology that uses electrolysis to attach a layer of the metal film to the surface of the metal, to prevent corrosion, and improve wear resistance, conductivity, reflectance, and beauty. Electroplating technology is widely used in zinc alloy die castings and aluminum alloy die castings.
Technological process:
Pretreatment → cyanide free alkali copper → cyanide free white copper tin → chromium plating
Advantage:
1. High gloss coating, high quality metal appearance;
2. The base materials are SUS, Al, Zn, Mg, etc; The cost is relatively low compared with PVD.
Disadvantages:
The environmental protection is poor and the risk of environmental pollution is high.
6. Powder spraying
Powder coating is sprayed on the surface of zinc alloy die castings and aluminum alloy die castings by powder spraying equipment (electrostatic plastic spraying machine). Under the action of static electricity, the powder will be evenly adsorbed on the surface of castings to form a powder coating; After high temperature baking, leveling and curing, the powder coating becomes the final coating with different effects (different kinds of effects of powder coating).
Technological process:
Loading → electrostatic dust removal → spraying → low temperature leveling → baking
Advantage:
1. Rich colors, highlights and mattes are available;
2. Low cost, suitable for building furniture products and shell of heat sink;
3. High utilization rate, 100% utilization, environmental protection;
4. Strong ability to cover defects;
5. Can imitate wood grain effect.
Disadvantages:
At present, it is seldom used in electronic products.
7. Metal drawing
It is a kind of surface treatment method to form lines on the surface of zinc alloy die castings by grinding products to achieve decorative effect. According to the different lines after wire drawing, it can be divided into: straight line wire drawing, random line wire drawing, ripple and spiral line.
Technical features:
Wire drawing treatment can make the metal surface obtain non mirror like metallic luster, and at the same time, wire drawing treatment can also eliminate the fine defects on the surface of zinc alloy die castings.
8. Sandblasting
It is a process that uses compressed air as power to form a high-speed spray beam to spray the sprayed material to the surface of zinc alloy die castings to be treated at a high speed, to change the appearance or shape of the outer surface of the surface of zinc alloy die castings and obtain a certain degree of cleanliness and different roughness.
Technical features:
1. Achieve different reflective or matte.
2. It can clean the micro burrs on the surface of zinc alloy die castings, make the surface of zinc alloy die castings more flat, eliminate the harm of burrs, and improve the grade of zinc alloy die castings.
3. Clear the residual dirt left during pretreatment, improve the finish of zinc alloy die castings, make zinc alloy die castings show uniform metal color, and make the appearance of zinc alloy die castings more beautiful.
9. Polishing
The surface modification of zinc alloy die castings using flexible polishing tools, abrasive particles or other polishing media. For different polishing processes: rough polishing (basic polishing process), medium polishing (finishing process) and fine polishing (polishing process), selecting appropriate polishing wheels can achieve the best polishing effect and improve the polishing efficiency at the same time.
Technical features:
Improve the dimensional accuracy or geometric accuracy of zinc alloy die castings, obtain smooth surface or mirror gloss, and eliminate gloss at the same time.
10. Etch
Generally, the term “etching” is also called photochemical etching, which refers to removing the protective film of the area to be etched after plate making and development by exposure, and contacting the chemical solution during etching, to dissolve the corrosion and form the effect of concave-convex or hollow forming.
Exposure method:
The project shall issue the material preparation size according to the drawing → material preparation → material cleaning → drying → coating or coating → drying → exposure → development → drying etching → film removal → OK.
Screen printing:
Material cutting → plate cleaning (stainless steel and other metal materials) → screen printing → etching → film removal → OK
Advantage:
1. It can be used for fine surface machining of zinc alloy die castings;
2. Give special effect to the surface of zinc alloy die castings;
Disadvantages:
Most of the corrosive liquids (acid, alkali, etc.) used in etching are harmful to the environment.