Spray painting improves the corrosion resistance, surface quality, and aesthetics of aluminium alloy die casting products. It forms a protective film on the surface of the casting, sealing pores to prevent oxidation. The process allows for precise coloring, complex structures, and a uniform, durable coating. Whether for functional or decorative use, spray painting is widely adopted across industries.
This article will cover the key aspects of spray painting in die casting aluminum components, including surface preparation, primer application, spraying techniques, and curing. Keep reading to learn how to achieve the ideal spray painting effect for your aluminium die casting components.
Spray Painting Process
Surface Preparation
Cleaning and Degreasing
Thorough cleaning with solvents or detergents can effectively remove oil, dust, and mold release agents.
This step ensures that the paint adheres firmly and prevents subsequent problems such as peeling or blistering, especially in metal die casting applications.
Mechanical Roughening
Sandblasting or shot blasting can roughen the surface, help the paint form a stronger mechanical bond with the die casting products, and remove light oxide layers or residual impurities.
Chemical Pretreatment
A mild acid etch removes the naturally occurring oxide layer on aluminium alloy die casting.
This step enhances surface activity, which improves adhesion between the primer and the substrate.
Drying Before Spray Painting
Residual moisture on the surface will affect the adhesion of the primer and topcoat.
Thorough drying of the casting using hot air or heating equipment is a key step before spray painting.
Primer
The Role of Primer
Primers can enhance the adhesion of the topcoat and play a corrosion protection role, especially for die casting parts used in harsh working environments.
It can also repair minor surface casting defects and improve the overall effect of the topcoat.
Primer Type: Epoxy Primer
Epoxy primer has excellent adhesion and chemical resistance, especially for aluminium die casting components, and can ensure a durable coating in industrial spraying.
Topcoat Spraying
Operation Specification
Topcoat spraying should be done with a professional spray gun, maintaining a spray distance of 15–25cm and a stable angle for uniform coating.
Air pressure, atomization, and spray width need to be adjusted in advance to ensure uniform atomization without large particles or rough edges.
Layered Spraying
The application should be done in 2–3 thin sprays rather than one thick spray.
After each layer, a flash time of 5–15 minutes must be reserved to allow the solvent to evaporate and to avoid bubbles and bulging of the coating.
Standing After Spraying
After all layers are applied, the workpiece should be left to stand for 15–30 minutes to allow the paint film to initially dry.
This process helps to improve the surface hardness and prevent scratches or damage during handling or transfer.
Curing and Drying
Natural Air Drying
Applicable to water-based or acrylic topcoats. It should be completed in a dust-free, well-ventilated environment to prevent dust from falling into the wet paint film and causing surface defects.
The air drying time is usually more than 24 hours, adjusted according to the type of paint and the ambient temperature and humidity.
Oven Curing
Applicable to solvent-based or high-performance topcoats, suitable for mass production.
Casting parts are placed in a hot air circulation oven, usually heated to 120–180°C, and the curing time is 20–40 minutes.
Oven curing is the most common and stable curing method for aluminium alloy die casting, which can significantly improve the hardness, adhesion, and durability of the coating.
Quality Control and Inspection
Adhesion Test
Cross-cut test and tape test are common methods for evaluating the adhesion of paint on die casting aluminum, which can help to find problems with topcoat spraying or primer selection.
Coating Thickness Measurement
Use a digital thickness gauge to detect the dry film thickness after spraying.
The appropriate coating thickness ensures the appearance of the die casting products and provides the necessary protection.
Appearance Defect Inspection
Visually inspect the surface of the die casting aluminum after painting for bubbles, sagging, color differences, and other problems.
Corrosion Resistance Test
Simulate long-term exposure to harsh environments through salt spray test or wet heat test, suitable for marine, outdoor, or industrial application scenarios.
Advantages of Spray Painting in Aluminum Die Castings
Enhance Corrosion Resistance
Spray painting forms a sealing coating that can prevent moisture and pollutants from penetrating porous aluminium die casting components, which is a key measure to extend the service life.
Improved Appearance
Paints can hide parting lines or pores, creating a smoother surface. In addition, customizable paint colors and textures can enhance the decorative value of die casting parts.
Improved Durability
Paints can provide enhanced resistance to scratches, abrasions, and UV rays, making them ideal for automotive parts, outdoor hardware, and consumer products made using the die casting process.
Reduced Maintenance Costs
Painted surfaces resist dust and are easy to clean. This helps reduce maintenance frequency and ensures long-lasting appearance and performance.
Die Casting Blank & Spray Painted Die Casting Part
Common Spray Painting Defects and Solutions
Peeling or Flaking
Usually caused by incomplete cleaning or failure to use a primer. Always follow complete pre-treatment and primer steps to prevent paint from peeling.
Bubbling or Foaming
The main cause is moisture or solvent residue in the substrate. Ensure thorough drying before spraying, and control humidity in the spray area.
Cracking
Spraying too thick or curing too quickly can cause cracking in the coating. Use thin, multiple coats and follow recommended curing times.
Uneven Coating
Often caused by inconsistent spraying action or pressure fluctuations. Spraying equipment should be calibrated regularly, and operators should be trained.
Conclusion
Spraying can improve the corrosion resistance, surface quality, and product life of aluminium alloy die casting.
To achieve the desired results, surface preparation, primer selection, spraying technology, and curing process need to be strictly controlled.
As a trusted die casting manufacturer, CEX Casting offers complete die casting services, from mold development to surface finish, tailored to your unique needs.
Contact us today to get expert support for your next metal die casting project.