11 Types of Die Casting Surface Finishes： A Comprehensive Selection Guide

Do your die-cast parts need surface finish treatment to enhance their visual appeal？ Are you looking for a suitable surface finish for your die casting parts to improve their properties？ If you still can’t make a decision when facing finish options, this article can enrich your knowledge of die casting surface finishes and help you choose the ideal one for your die casting parts.

Abrasive Blasting

Abrasive blasting is a process of blasting abrasive material(such as sand and glass beads)at a high speed onto the surface of die-cast parts. With the function of impact and cutting, abrasive blasting can remove burrs and flash from the surface of die-cast parts. It can make the surface rougher, improving paint adhesion and facilitating further surface treatment. At the same time, it can also remove the surface oxide layer, oil dust, old coating, and etc.

The main advantage of abrasive blasting is its low cost, because its equipment is simple. Meanwhile, the surface roughness of the die-cast parts is controllable during the abrasive blasting process.

Abrasive blasting has many types for you to apply in treating different kinds of die casting parts. The most common types are shot blasting and sand blasting.

Shot Blasting

Shot blasting removes surface oxidation, impurities, and roughness by spraying high-speed shot particles, improving surface quality. The abrasives used in shot blasting are typically metal shot, ceramic shot, glass beads, etc. The shape of the abrasive is usually spherical. 

Shot blasting can remove oxide scale and burrs from the surface of die-cast parts, improve paint adhesion, and provide a foundation for subsequent electroplating and spraying. Shot blasting has a high impact on castings and is suitable for structural parts and large die castings.

Advantage：

Shot blasting has a good cleaning effect on the surface of die-cast parts and can improve their fatigue life. Using glass beads or ceramic shot as abrasives, shot blasting can give the surface of die-cast parts a fine matte finish.

Application：

• Automotive industry: For die-cast automotive parts, steel shot can be selected as an abrasive for surface strengthening treatment.
• Electronic products: Shot blasting of zinc alloy connector housings to enhance adhesion before electroplating.
• Building hardware: Shot blasting treatment for die-cast door and window hardware and bathroom fittings can provide a decorative matte finish.

Sand Blasting

Although it includes “sand” in its name,  the abrasives used in sand blasting are not limited to sand. It also includes aluminum oxide sand, glass beads, ceramic sand, plastic particles, etc. Whether your castings need to be cleaned of surface scale, oil stains, or old coatings, sand blasting can achieve excellent cleaning results.

In addition, sand blasting can improve surface roughness, enhance coating adhesion, or provide a textured effect for your castings. Abrasives for sandblasting are usually granular with moderate impact strength. It can be used for thin-walled die castings.

Advantages:

Even complex structural die castings with narrow gaps can be cleaned in all directions by sandblasting. There is no wastewater discharge from sandblasting, and part of the blast material can be recycled, making it more environmentally friendly.

Application:

• Electronics industry: Cleaning tiny impurities on the surface of circuit boards or precision components.
• Automotive industry: Strengthen gears and other key components to extend service life.
• Aerospace: Improve the anti-fatigue performance of aircraft engine blades, landing gears, and other metal parts.

Ultrasonic Cleaning

Ultrasonic cleaning is a method used to clean the surfaces of die-cast parts. It involves generating microscopic bubbles in the cleaning solution using high-frequency sound waves and utilizing the impact force released when the bubbles burst to remove oil stains, release agents, and other contaminants from the surface of the workpiece.

If your castings have large particles of debris on their surfaces, you can opt for ultrasonic waves with a frequency of 20–30 kHz. If you require precise cleaning of small, delicate parts, you will need to use high-frequency sound waves above 40 kHz.

You can choose different cleaning solutions according to your cleaning needs, including alkaline solutions, acidic solutions, and deionized water.

Advantages:

• Suitable for complex castings: Ultrasonic cleaning can efficiently clean the threads or holes in your castings.
• No damage to castings: If you do not want mechanical cleaning to leave scratches on the surface of your castings, ultrasonic cleaning generally does not cause mechanical damage.

Application:

Ultrasonic cleaning can be used to remove mold release agents from the surface of castings, providing a foundation for subsequent electroplating and spraying. In the post-processing stage, impurities can be removed from die-cast parts after heat treatment.

Electroplating

Electroplating is one of the most commonly used die casting surface treatments. It is a process that uses electric current to deposit metal on the surface of die castings. The castings are immersed in a solution containing metal ions, which are reduced and gradually form a metal coating on the surface.

Zinc alloy(such as Zamak 3, Zamak 5)die-cast parts are most commonly treated with electroplating for surface finishing, as zinc alloy surfaces are highly reactive and easily achieve uniform coatings. Zinc alloys are typically electroplated with copper to enhance corrosion resistance. Aluminum alloy die-cast parts are also frequently electroplated, but require prior zinc immersion treatment.

Advantage:

Die-cast parts treated with electroplating processes have improved electrical conductivity, resistance to wear and corrosion, and anti-rust properties. If the die cast parts are electroplated with metals such as gold, silver, or nickel, the aesthetic appeal can also be enhanced.

Application:

• Electric Components: As electroplating can improve the electrical conductivity of die-cast metal parts, it is very suitable for connectors, circuit boards, switches, etc.
• Automotive Components: In the automotive industry, electroplating is applied to the die-cast decorative parts, such as trims and emblems. Sometimes, electroplating is also used to treat the surface of automotive hardware.

Electrophoresis

Electrophoresis is also called e-coating or electrocoating. Electrophoresis is a process that uses an electric field to deposit charged particles onto a conductive surface. It can apply a thin coating to die-cast parts, typically ranging from 0.0002 to 0.002 inches in thickness. Even on complex-shaped castings, electrophoresis can form a uniform coating.

Advantages:

The surface of electrocoated die-cast parts is extremely robust, providing excellent protection. Wear resistance is significantly enhanced, ensuring that the die-cast parts remain intact even in environments with frequent friction. It can also improve the corrosion resistance of the parts, making them perform excellently even in salt spray or moisture environments.

Applications：

• Automotive Industry: Aluminum die castings with electrophoretic coating have excellent hardness and are suitable for automotive components, such as chassis, suspension assemblies, and brackets.
• Electronic Components: Die-cast parts coated by electrophoresis have good conductivity and are suitable for various small electronic components, such as connectors.

Powder Coating

Powder coating is a surface treatment process that involves spraying dry powder coating onto the surface of die-cast parts through electrostatic adsorption, followed by high-temperature curing to form a uniform coating.

Advantage:

By powder coating, the die castings can improve corrosion resistance. They can be used in even salt fog or chemical corrosion environments. The die-cast parts can be more durable and scratch-resistant with powder coating, promising a long lifespan. Powder coating offers a wide range of color options for die-cast parts, and the colors produced by powder coating are highly consistent. Powder coating is also environmentally friendly and can reach the standard of RoHS/REACH.

Applications:

• Automotive Industry: As the die casting parts with powder coating are durable and scratch resistant, they can be applied to wheels, chassis, and other external parts that reflect ultraviolet rays.
• Home Appliances: Powder coating can be applied to the outer surfaces of die-cast electrical enclosures, such as washing machines, refrigerators, for wear resistance.
• Consumer Electronics: Spray ultra-fine powder on die-cast electronic device parts, such as mobile phone shells and laptop shells, can prevent fingerprints.

Painting

Painting involves using spraying equipment to evenly coat the surface of die-cast parts with paint, which is then cured to form a protective or decorative coating. Typically, the die-cast parts need to be pretreated to ensure proper paint adhesion. The paint is then sprayed, brushed, or dipped onto the parts. Common liquid coatings include polyurethane paint and epoxy resin paint, which can meet the scratch-resistant and anti-corrosion requirements. For its various color options, painting can also enhance the decorative function of die-cast parts made of aluminum alloy, zinc alloy, magnesium alloy, etc.

Advantages:

Choosing painting as your die-cast parts’ surface finish has many benefits. If you don’t have a big budget, painting is very cost-effective. In terms of the impact of painting on the appearance of die-cast parts, there are many colors available. If the paint peels off, it can be repainted, making it easy to maintain.

Applications：

• Automotive Industry: Painting can be applied to die-cast body panels for its various color choices.
• Mechanical Industry: The anti-rust and corrosion-resistant properties of painting make it suitable for the mechanical industry. You can also use painting for die-cast parts’ color coding and identification.

Polishing

Polishing can offer the die-cast components a smooth and bright mirror-like surface finish. Physical polishing refers to the removal of surface irregularities from die-cast parts through physical friction, typically using tools such as grinding wheels, sanding belts, and polishing wheels. Chemical polishing involves dissolving the protrusions on the surface of die-cast parts using acidic or alkaline solutions to smooth the surface. In addition, there are other polishing methods such as electrolytic polishing and vibratory polishing. Typically, the values of polishing finish can be less than Ra 0.02µm. 

Advantages:

Polishing offers the die-cast parts an aesthetic appeal as well as corrosion protection and durability.

Application：

• Home and Bathroom Hardware: Zinc alloy die-cast faucets and door handles can be chrome-plated after polishing to give them a luxurious sheen.
• Automotive Trim: Die-cast aluminum alloy automotive interior trim is coated after polishing to make it weather-resistant and scratch-resistant.

Passivating

Passivating is a process of immersing die-cast parts in chromic acid solution to form a protective oxide layer. Zinc alloys (Zamak 3,5) and aluminum alloys (ADC12, A380) die-cast parts can be passivated to improve the corrosion resistance. But for aluminum alloys, chromate passivation has poor environmental performance and is gradually being replaced by chromium-free processes.

Advantages:

After passivation treatment, the corrosion resistance and anti-rust properties can be significantly improved, especially the corrosion resistance. The die-cast parts become more durable, extending their service life.

Applications:

• Medical Devices: Passivation treatment provides excellent corrosion resistance and cleanliness for die-cast medical devices, ensuring safety.
• Food Processing Equipment: Because die-cast parts treated with passivation have excellent corrosion resistance and cleanliness, die-cast components for food processing equipment can ensure food safety.
• Marine Component: Die-cast parts with a passivating finish can bear harsh marine weather and withstand saltwater corrosion. 

Physical Vapor Deposition（PVD）

PVD is a process in which coating materials are converted from a solid state to a gaseous state through physical means, and then condensed into a dense film on the surface of the die-cast parts. The entire PVD process is carried out under vacuum conditions.PVD could precisely control the thickness and composition of the die-cast parts coating.

Advantages： Die-cast parts treated with PVD show significant improvements in hardness and wear resistance. Additionally, PVD offers a variety of color options for die-cast parts, such as gold, silver, etc. If your project has environmental requirements, PVD is an excellent choice.

Application:

• Hardware: Die-cast parts treated with PVD surface finish have significantly improved hardness and are suitable for various cutting tools, drill bits, and saw blades.
• Electronics Industry: PVD could enhance the wear-resistance, even die-cast electronic devices and components subjected to vibration will not be easily damaged.

Anodizing

Anodizing is an electrochemical method that forms a protective oxide layer on metal surfaces, primarily applied to aluminum and its alloy die castings. However, the aluminum alloy commonly used for die casting, ADC12, has high copper and silicon content. Copper can damage the anodizing electrolyte, while silicon can cause the oxide film to turn black. Aluminum alloys containing manganese and cobalt can be anodized, such as DM6 or DM32, but aluminum alloys without silicon have poorer fluidity.

Advantage：

The anodizing process enhances the hardness of die-cast components, improving their scratch and wear resistance. Additionally, anodizing provides extensive color customization possibilities.

Application：

• Electronics Industry: Anodizing forms an insulating oxide film on the surface of die-cast aluminum capacitor housings. It can also be used to form anti-fingerprint films on mobile phone/laptop casings through anodizing, and offers color options such as rose gold and gray.
• Aerospace: Hard anodizing used on die-cast airframe structural components reduces weight and enhances corrosion resistance. It also enhances the performance of die-cast spacecraft casings in extreme temperatures.

Laser

Laser is a beam of light that is highly concentrated and has little dispersion. It can vaporize materials instantly. In die casting surface treatment, laser is mainly used for cleaning, deburring, and strengthening. 

Laser Cleaning

It uses a high-energy laser beam focused onto the surface to instantly vaporize or peel off oxide layers and oil stains. This method is suitable for die casting parts with a large amount of residual material and a large pouring port that is not easy to remove manually.

Advantages:

• Precise cleaning: Use laser equipment to clean specific areas of die-cast parts.
• Non-contact: Avoid physical friction damage.
• Environmentally friendly: No liquid waste is produced.

Laser Deburring

The presence of burrs on the surface of castings increase the cost of subsequent processes (CNC machining). Burrs also pose safety hazards and affects assembly accuracy. Lasers can melt burrs on the surface of castings and the liquid metal smooths itself out to create round edges. 

Advantages:

Laser deburring is suitable for aluminum die casting part surface treatment. It will not produce grinding dust during the process, which is environmentally friendly. If your highly stressed components, such as chassis parts, need to be enhanced in fatigue strength, laser deburring can be an ideal choice.

Laser Strengthening

It means using lasers for surface strengthening by altering the microstructure of the surface through laser engraving or cladding to form specific textures or reinforced layers.

Advantages:

Whether you want to add anti-slip patterns or engrave brand logos to the surface of die-cast parts, laser strengthening can meet your processing needs for casting textures. In addition, it can also harden castings and increase their wear resistance.

Conclusion

In summary, there are many different surface treatment methods for die-cast parts, which can meet your various requirements in terms of application environment, mechanical properties, and color. If you still have questions about the finish options for die-cast parts, please feel free to contact Sunrise Metal. Sunrise is a professional die casting manufacturer in China and can customize surface finishes tailored to your requirements.