How to prevent zinc alloy die-cast bag accessories from oxidizing and fading?
Release Time : 2025-09-18
Zinc alloy die-cast bag accessories are prone to surface discoloration due to oxidation over long-term use, affecting their aesthetics and durability. Anti-oxidation treatment requires a multi-faceted approach that combines material properties, process optimization, and environmental adaptability, using physical isolation, chemical conversion, and structural reinforcement to create a long-lasting protective system. This process must balance the precise structure of the die-cast part with the decorative requirements of the bag accessories, ensuring a tight bond between the protective layer and the substrate while also meeting the fashion industry's stringent color durability requirements.
The unique characteristics of the zinc alloy die-casting process place higher demands on surface treatment. During the die-casting process, molten metal rapidly fills the mold cavity under high pressure, easily forming microscopic defects such as micropores and cold shuts. These defects can serve as pathways for corrosive media to penetrate. Therefore, pre-treatment requires mechanical methods such as sandblasting and polishing to eliminate surface imperfections, followed by ultrasonic cleaning to remove oil and impurities, providing a clean substrate for the subsequent deposition of the protective layer. Incomplete pre-treatment can accelerate localized oxidation due to substrate defects, even with advanced protective processes.
Electroplating is a key method for improving the corrosion resistance of zinc alloy bag accessories. Electrolytic deposition of metal coatings such as chromium, nickel, and zinc on surfaces creates a dense physical barrier. For example, nickel coatings are renowned for their excellent chemical stability, effectively resisting corrosion from acidic substances such as sweat and cosmetics. Chromium coatings enhance their self-healing ability by forming a passivation film. Even with minor scratches, the surrounding chromium migrates to the damaged area to form a new protective layer. The electroplating process requires strict control of current density and temperature to avoid coarse crystallization and increased porosity in the coating. Furthermore, a multi-layer plating structure is employed, with primers enhancing adhesion and topcoats providing decorative effects, achieving a balance between functionality and aesthetics.
Chemical conversion coatings offer a cost-effective protective solution for zinc alloy bag accessories. Traditional chromate treatments, which chemically react to form a chromium-containing complex salt film on the metal surface, offer both corrosion resistance and conductivity. However, due to the environmental risks associated with the presence of hexavalent chromium, they are being gradually replaced by chromium-free passivation technologies. New silane treatments form a three-dimensional network structure through hydrolysis and polycondensation, offering corrosion resistance similar to that of chromate coatings and complying with RoHS directive requirements. For accessories requiring a colorful effect, micro-arc oxidation technology can be used. This technology creates a ceramic oxide film on the metal surface under the action of a high-voltage electric field. Special effects such as gold and silver can be achieved by adding pigments. The film also boasts a hardness exceeding HV1000, significantly improving wear resistance.
Spray coating provides personalized protection and decorative options for zinc alloy bag accessories. Coatings such as epoxy resin and polyurethane form a continuous insulating film, effectively shielding against corrosive media such as water and oxygen. Electrostatic spraying uses a high-voltage electrostatic field to uniformly adhere powder coating to the accessory surface. After high-temperature curing, a smooth coating forms, offering salt spray resistance several times greater than traditional spray painting. For high-end products, a combined vacuum coating and spray coating process can be employed. First, a metallic reflective layer is deposited through vacuum evaporation, followed by a clear protective lacquer. This creates a metallic finish while enhancing weather resistance, meeting the stringent gloss requirements of fashion bags.
Environmental management is key to extending the protective life of zinc alloy bag accessories. Consumers should avoid prolonged contact with chemicals such as perfume and sunscreen, as the organic solvents in these substances can damage the coating structure and accelerate oxidation. When cleaning, gently wipe with a soft cloth dampened with neutral detergent. Steel wool or chlorine-containing cleaners are strictly prohibited to prevent scratching the surface and causing electrochemical corrosion. When storing, accessories should be kept in a dry environment and avoid contact with materials that easily release sulfides, such as rubber and leather, to prevent electrochemical corrosion and discoloration.
From a materials research and development perspective, optimizing the composition of zinc alloys is the fundamental way to improve corrosion resistance. By adjusting the ratio of elements such as aluminum, copper, and magnesium, the grain structure can be refined, reducing the occurrence of microscopic galvanic corrosion. For example, ZA8 zinc-aluminum alloy, due to its high aluminum content, forms a more stable aluminum oxide protective film on its surface, resulting in significantly better corrosion resistance than ordinary zinc alloys. Furthermore, the addition of rare earth elements to the alloy can purify grain boundaries, strengthen the bonding between the coating and the substrate, and provide material-level protection against oxidation and discoloration.