Anti-paint-peeling solutions for aluminum alloys, galvanized sheets, and stainless steel: Application guidelines for specialized epoxy primers and zinc-rich epoxy primers.

How to solve the problem of paint adhesion on aluminum alloys, galvanized sheets, and stainless steel? In painting projects, aluminum alloys, galvanized materials, and stainless steel are often referred to as “difficult-to-coat substrates.” These metals have extremely smooth surfaces and unique properties, making it difficult for ordinary anti-rust paints to form effective molecular bonds, leading to large-scale peeling and flaking of the paint film shortly after use. Addressing this industry pain point, choosing a suitable primer solution is not only an aesthetic requirement but also crucial for extending the service life of components. 1. Surface sanding 2. Spraying a special primer 3. Spraying a topcoat I. Why do these substrates have poor adhesion? Aluminum alloys: A dense aluminum oxide film easily forms on the surface. While this film provides corrosion protection, it is also repellent, preventing ordinary paint from adhering properly. Galvanized materials: The zinc content in the galvanized layer is extremely high. Its surface often carries passivation liquid or oil stains from processing and has strong chemical reactivity, easily reacting with acidic paints through saponification. Stainless steel: The material structure is dense and the surface is extremely smooth, lacking sufficient physical roughness to provide mechanical bonding force. II. Core Solution: Selection of Specialized Primers To ensure a stable coating film, coating processes typically fall into two main categories: 1. Epoxy Zinc Phosphate Primer This is a universal choice for both light and non-ferrous metals. Epoxy zinc phosphate primers possess excellent anti-permeability and chemical stability. Advantages: Zinc phosphate has a passivating effect, establishing a good adhesion foundation without damaging the substrate, and it has excellent compatibility with various topcoats (such as polyurethane topcoats and fluorocarbon topcoats). 2. Specialized Epoxy Primer For extremely slippery surfaces that are difficult to adhere to, using specialized epoxy primers containing special functional groups is a more reliable approach. These primers typically contain additives that enhance polarity, enabling chemical chelation with atoms on the metal surface and completely solving the problem of peeling. III. Special Requirements: When Epoxy Zinc-Rich Primer Must Be Used In certain projects with high corrosion resistance requirements (such as heavy industrial equipment and marine environments), the designer may explicitly require the use of epoxy zinc-rich primer. Although zinc-rich primer is mainly used for cathodic protection of carbon steel, when used on aluminum alloys or galvanized sheets, the following construction prerequisites must be strictly adhered to: Key Steps: Grind or sandblast before application. Physical Pretreatment: Because zinc-rich primer needs direct contact with the metal substrate to exert its electrochemical protective effect, and it requires a high surface roughness, the substrate surface must be treated to Sa 2.5 grade or a certain roughness (usually recommended to be $30-50 \mu \m$) through mechanical grinding or sandblasting. Precautions: For galvanized layers, handle with care during grinding to avoid excessive grinding that could thin the zinc layer or damage the substrate. Stainless steel, aluminum alloy, zinc alloy, and other metal materials. Applying red paint to stainless steel, aluminum alloy, and zinc alloy. IV. Construction Suggestions and Summary. Cleaning and Degreasing: Regardless of the primer used, a special cleaning agent must be used to remove surface oil and fingerprints before application. Environmental Control: The ambient humidity during application is recommended to be below 85%, and the substrate temperature should be 3°C above the dew point. Recommended Solutions: Civil/General Industrial Use: “Special Epoxy Primer” or “Epoxy Zinc Phosphate Primer” is recommended as the first choice, saving time and effort. High Corrosion Resistance Heavy Industry: If zinc-rich coatings are required, remember to sandblast and polish; do not cut corners. With the correct coating solution and rigorous surface treatment, even “tough nuts to crack” like aluminum alloys and galvanized sheets can achieve durable coating protection. Related Readings: Complete Analysis of Electroplated Metallic Paint Application Process; How to Apply Gloss (Clear Varnish) to Metallic Paint; Analysis of the Process and Application of Spraying Colored Metallic Paint on Polished Stainless Steel Parts; Process and Application of Creating Metallic Antique Effects on Various Materials.