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What surface treatment can be used for zinc alloy die castings?

Update:05-03-2021
Summary:

Surface treatment, bai, is to form a surface layer with one or more special properties on the surface of the zinc alloy die casting by physical or chemical methods. Surface treatment can improve product appearance, texture, function and other aspects of performance.
1. Anodizing
It is mainly the anodizing of aluminum alloy die castings, and zinc alloy die castings cannot be made for the time being due to technical reasons. It uses electrochemical principles to form a layer of Al2O3 (alumina) film on the surface of aluminum alloy die castings. This oxide film has special characteristics such as protection, decoration, insulation, and abrasion resistance.
Single color, gradient color:
Polishing / sandblasting / wire drawing → degreasing → anodizing → neutralization → dyeing → sealing → drying
Two colors:
①Polishing/sandblasting/wire drawing→degreasing→masking→anodic oxidation 1→anodic oxidation 2→sealing→drying
②Polishing/sandblasting/wire drawing → degreasing → anodizing 1 → laser carving → anodizing 2 → sealing → drying
Technical features:
1. Improve strength
2. Realize any color except white
3. Achieve nickel-free sealing and meet the requirements for nickel-free in Europe, the United States and other countries
Technical difficulties and key points of improvement:
The yield level of anodizing is related to the cost of the final product. The focus of improving the yield of oxidation is the appropriate amount of oxidant, appropriate temperature and current density. This requires aluminum alloy die-casting plants to continuously explore and seek breakthroughs in the production process.
Two, electrophoresis
Used for stainless steel, aluminum alloy die-casting parts, zinc alloy die-casting parts, etc., can make the product show various colors, and maintain the metallic luster, at the same time enhance the surface performance, and have better anti-corrosion performance.
Process flow:
Pretreatment → electrophoresis → drying
advantage:
1. Rich colors;
2. No metal texture, can be used with sandblasting, polishing, wire drawing, etc.;
3. Processing in a liquid environment can realize surface treatment of complex structures;
4. The technology is mature and can be mass-produced.
Disadvantages:
The ability to conceal defects is average, and electrophoresis for die castings requires higher pre-treatment.
3. Micro arc oxidation
The process of applying a high voltage in an electrolyte solution (usually a weak alkaline solution) to form a ceramicized surface film. This process is the result of the synergistic effect of physical discharge and electrochemical oxidation.
Process flow:
Pretreatment→hot water washing→MAO→drying
advantage:
1. Ceramic texture, dull appearance, no high-gloss products, fine touch, anti-fingerprint;
2. Wide range of base materials: Al, Ti, Zn, Zr, Mg, Nb, and their alloys, etc.;
3. The pretreatment is simple, the product has excellent corrosion resistance and weather resistance, and good heat dissipation performance.
Disadvantages:
At present, the colors are limited, only black and gray are more mature. Bright colors are currently difficult to achieve; the cost is mainly affected by high power consumption, and it is one of the most expensive surface treatments.
Four, PVD vacuum plating
The full name is physical vapor deposition, which is an industrial manufacturing process that mainly uses physical processes to deposit thin films. All kinds of zinc alloy die castings and aluminum alloy die castings can be vacuum electroplated.
Process flow:
Cleaning before PVDSanitary wares decoration PVD vacuum coating system → vacuuming in the furnace → cleaning target and ion cleaning → coating → coating finished, cooling out of the furnace → post-processing (polishing, AFP)
Technical features:
PVD (Physical Vapor Deposition, physical vapor deposition) can be coated on the metal surface with high-hardness, high wear resistance cermet decorative coating
Five, electroplating
It is a technology that uses electrolysis to attach a metal film to the surface of the metal to prevent corrosion, improve wear resistance, electrical conductivity, reflectivity, and enhance aesthetics. Electroplating technology is widely used in many Both zinc alloy die castings and aluminum alloy die castings can be applied.
Process flow:
Pretreatment→Cyanide-free alkaline copper→Cyanide-free copper-nickel alloy tin→Chrome plating
advantage:
1. The coating has high gloss and high-quality metal appearance;
2. The base material is SUS, Al, Zn, Mg, etc.; the cost is relatively low compared to PVD.
Disadvantages:
Environmental protection is poor, and environmental pollution risks are greater.
Six, powder coating
Powder coating equipment (electrostatic spraying machine) is used to spray powder coating on the surface of zinc alloy die castings and aluminum alloy die castings. Under the action of static electricity, the powder will be uniformly absorbed on the surface of the casting to form a powdery coating; After high-temperature baking, leveling and curing, the shaped coating becomes the final coating with different effects (different types of powder coating effects).
Process flow:
Upper part → electrostatic dust removal → spraying → low temperature leveling → baking
advantage:
1. Rich colors, high gloss and matte finish are optional;
2. The cost is low, and it is suitable for the shell of building furniture products and heat sinks, etc.;
3. High utilization rate, 100% utilization, environmental protection;
4. Strong ability to hide defects;
5. The wood grain effect can be imitated.
Disadvantages:
Currently used in electronic products is relatively small.
Seven, metal wire drawing
It is a surface treatment method that forms lines on the surface of zinc alloy die castings by grinding products to achieve a decorative effect. According to the different lines after drawing, it can be divided into: straight drawing, chaotic drawing, corrugation, and swirling.
Technical features:
The wire drawing treatment can make the metal surface obtain a non-mirror-like metallic luster, and the wire drawing treatment can also eliminate the fine defects on the surface of the zinc alloy die casting.
8. Sandblasting
It uses compressed air as power to form a high-speed jet beam to spray the spray material on the surface of the zinc alloy die casting to be processed at high speed, so that the appearance or shape of the outer surface of the zinc alloy die casting surface is changed, and a certain degree of cleanliness and different A process of roughness.
Technical features:
1. Realize different reflective or matt.
2. It can clean up the tiny burrs on the surface of zinc alloy die castings, make the surface of zinc alloy die castings more smooth, eliminate the hazards of burrs, and improve the grade of zinc alloy die castings.
3. Clear the residue left over from the pretreatment, improve the finish of the zinc alloy die casting, and make the zinc alloy die casting show a uniform and consistent metal color, making the appearance of the zinc alloy die casting more beautiful and attractive.
Nine, polishing
Use flexible polishing tools and abrasive particles or other polishing media to modify the surface of zinc alloy die castings. For different polishing processes: rough polishing (basic polishing process), medium polishing (finishing process) and fine polishing (coating process), choosing a suitable polishing wheel can achieve the best polishing effect and improve polishing efficiency.
Technical features:
Improve the dimensional accuracy or geometric shape accuracy of zinc alloy die castings to obtain a smooth surface or mirror gloss, and at the same time, it can eliminate the gloss.
10. Etching
Generally referred to as etching is also called photochemical etching, which refers to the removal of the protective film of the area to be etched after exposure, plate making and development, and contact with chemical solutions during etching to achieve the effect of dissolving and corroding, forming unevenness or hollowing out.
Exposure method:
According to the figure, the project prepares the size of the material → material preparation → material cleaning → drying → film or coating → drying → exposure → development → drying-etching → stripping → OK.
Screen printing method:
Cutting → cleaning the plate (stainless steel and other metal materials) → screen printing → etching → stripping → OK
advantage:
1. The surface of zinc alloy die-casting parts can be finely processed;
2. Give special effects to the surface of zinc alloy die castings;
Disadvantages:
Most of the corrosive liquids (acids, alkalis, etc.) used in etching are harmful to the environment.

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