Nowadays, die-cast aluminum alloy parts are widely used in multiple fields.  Appropriate surface treatment is crucial for them.  Different methods will bring different properties and appearances, affecting product quality and competitiveness.  This article explains various surface treatment methods to help you make a reasonable decision when producing or choosing aluminum alloy die-cast parts.

Surface Treatment Techniques Used for Die - Cast Aluminum Alloys

Anodizing Process

• Process Overview: A layer of oxide film is formed on the surface of aluminum alloy by applying high-voltage electricity.

• Process Characteristics: The oxide film has high hardness, is resistant to scratch and abrasion, has strong dyeability with rich colors, has good corrosion resistance, can adapt to various environments, and has good insulating performance.

• Scope of Application: Electronic product casings, such as mobile phones, tablet computers, laptops, etc.;   automobile parts, such as wheels, decorative strips, interior parts, etc.;   household items, such as lamp casings, furniture hardware, etc.;   sports equipment, such as bicycle parts, fitness equipment, etc.;   some small aluminum alloy parts in the aerospace field.

Micro-arc Oxidation Process

• Process Overview: Under high voltage, micro-arc discharge is generated on the surface of die-cast aluminum alloy to form a ceramic oxide film. 

•  Process Characteristics: The film has good properties: excellent hardness, wear resistance, corrosion resistance, insulation, and thermal shock resistance. It has a strong bonding force. The process is environmentally friendly. The characteristics of the film can be adjusted and controlled. 

•  Scope of Application: Aluminum alloy components related to aerospace, automotive, military, electronics, and electrical fields.

Powder Spraying Process

• Process overview: The powder coating is electrostatically adsorbed and cured at high temperatures. 

•  Process characteristics: The coating has strong adhesion and cannot easily fall off. Various coatings types can meet performance requirements, such as corrosion resistance, wear resistance, and weather resistance. There is a wide range of color choices and various appearance effects. It can cover workpieces with complex shapes, and the coating is uniform. It has good environmental protection performance, and the powder can be recycled. 

•  Scope of application: Doors, windows, curtain walls, frames, electrical appliance housings, equipment housings, and components.

Electroplating Process

• Process Overview: Electroplating is depositing a layer of metal coating on the surface of aluminum alloy using the electrolysis principle. 

•  Process Characteristics: It can endow the surface of aluminum alloy with luster and present various metal colors. It can improve the surface hardness and wear resistance. The thickness of the coating can be precisely controlled. 

•  Scope of Application: Automobile wheels, car logos, mobile phone cases, faucets, shower heads, handles, jewelry, ornaments, and high-end hardware products to highlight the metallic texture.

Electrophoresis Process

• Process overview: The die cast aluminum alloy workpiece is placed as an electrode in an electrophoretic paint solution containing resin particles. Under the action of an electric field, the resin particles in the paint solution are deposited on the surface of the aluminum alloy to form a coating. 

•  Process characteristics: The coating is uniform, has high corrosion resistance, and is environmentally friendly. 

• Scope of application: Automobile, electrical appliance, and construction industries.

Baking Finish Process

• Process overview: Firstly, pre-treat the surface of die-cast aluminum alloy by cleaning and removing rust. Then, spray specific coatings. Finally, it is put into a high-temperature oven for baking to make the coatings solidify into a firm paint surface. 

•  Process characteristics: The paint surface is smooth and flat with high glossiness. It has good hardness, wear resistance, and is anti-scratch. The colors are bright and long-lasting. It has good waterproof and moisture-proof performance to prevent water erosion. Unique textures and effects can be achieved. 

•  Scope of application: Aluminum alloy dining chair frames, supports of folding tables, high-end speaker casings, and computer monitor supports. Strap buckles, upright poles of scooters, aluminum alloy flashlight casings, thermos cup casings.

Sandblasting Process

• Process overview: Use high-speed sprayed sand particles to impact the surface of die-cast aluminum alloy. The roughness and effect of the surface can be controlled by adjusting parameters such as the size of sand particles, spraying pressure, and angle. 

•  Process characteristics: Uniform roughness enhances the adhesion of the coating. Improves the surface cleanliness. Creates a unique matte effect with a firm appearance texture. The process is relatively simple and has a relatively low cost. 

•  Scope of application: Motor housings, aluminum alloy door bolts, table lamp housings, photo frame borders, USB flash drive housings, spare parts.

Chemical Passivation Process

• Process overview: Immerse the aluminum alloy die casting into a solution containing specific chemical reagents, and a passivation film is generated on the surface of the aluminum alloy through a chemical reaction. 

• Process characteristics: A dense passivation film is formed with anti-corrosion solid ability and good durability in different climatic environments. It is simple to operate and has a low cost. 

•  Scope of application: Heat sinks, pipes, valves, door and window accessories.

Electroless Plating Process

• Process overview: Electroless plating is a process in which, without an external current, a suitable reducing agent is used to reduce and deposit metal ions in the plating solution onto the surface of the die-cast aluminum alloy to form a metal coating. 

•  Process characteristics: The coating has good uniformity and can meet the coating requirements of complex structures. A strong bonding force exists between the coating and the die-cast aluminum alloy substrate, making the coating not easy to fall off. Various materials are available for plating: multiple metal and alloy coatings, such as nickel, copper, etc., can be deposited. It can improve its electrical conductivity. 

•  Scope of application: Computer motherboards, mobile phone circuit boards, electronic connectors, automotive parts.

Nitriding Treatment Process

• Process overview: Die-cast aluminum alloy is placed in a nitrogen-containing medium. Under certain conditions, nitrogen atoms permeate the surface to form a nitride layer. 

•  Process characteristics: High surface hardness, good corrosion resistance, and improved fatigue performance. 

•  Scope of application: Mold industry, mechanical parts, and automotive parts.

Chemical Polishing Process

• Process overview: The die-cast aluminum alloy workpiece is immersed in a polishing solution containing strong acids and additives. Under certain conditions, a reaction occurs, dissolving the microscopic protruding parts to reduce the roughness. The additives' synergistic effect makes the surface bright and flat. 

•  Process characteristics: Simple operation, good polishing effect, relatively low cost, and limitations in terms of environmental protection. 

•  Scope of application: Decorative parts, parts with complex structures, and parts for mass production.

Mechanical Polishing Process

• Process overview: Use polishing tools to rub against the surface of die-cast aluminum alloy and, with the help of media, remove flaws, etc., to make the surface smooth and shiny. 

•  Process characteristics: The precision can be controlled, and high smoothness and glossiness can be achieved. Limitation: It isn't easy to uniformly polish workpieces with complex shapes. 

•  Scope of application: Optical elements, optical instruments, precision parts, shafts, gears, high-end decorations, watch cases, and jewelry boxes.

Laser Surface Treatment Process

• Process overview: A laser beam with high energy density is used to irradiate the surface of die-cast aluminum alloy, causing physical or chemical changes on the surface of the aluminum alloy and thus changing its surface properties. 

•  Process characteristics: High precision, non-contact, and capable of achieving multiple treatment effects. 

•  Scope of application: Aerospace, automobile manufacturing, and precision machinery fields.

Wire Drawing Process

• Process overview: Through the wire drawing wheel or wire drawing belt on the wire drawing equipment, the surface of the workpiece is rubbed in a specific direction to form uniform and fine lines on the surface. 

•  Process characteristics: It can produce various line effects such as straight lines, random lines, corrugated lines, etc., and is wear-resistant and anti-fingerprint. 

•  Scope of application: Aluminum alloy mobile phones and tablet casings, household appliance panels, aluminum alloy decorative parts, and decorative strips inside cars.

Comparison of the Advantages and Disadvantages of Various Surface Treatment Processes

Cost Comparison

Processes with low cost: sandblasting process, chemical passivation process, chemical polishing process, electrophoresis process. Processes with a high cost: micro-arc oxidation process, nitriding treatment process, laser surface treatment process, some electroplating processes (such as special electroplatings like gold plating and silver plating), high-end baking finish process.

Performance Comparison

Good wear resistance: micro-arc oxidation process, nitriding treatment process, baking finish process, electroplating process, mechanical polishing process. Good corrosion resistance: micro-arc oxidation process, anodizing process, powder spraying process, electrophoresis process, chemical passivation process, electroless plating process. Good comprehensive performance (hardness, heat resistance, bonding force, etc.): micro-arc oxidation, nitriding, laser surface treatment process.

Different Usage Environments and Suitable Processes

Outdoor Environment (Such as Aluminum Alloy Components on Exterior Walls)

Powder spraying process: It has good weather and corrosion resistance, can resist the erosion of ultraviolet rays, wind, and rain for a long time, has a variety of color options, and the coating is not easy to fade. Anodizing process: The oxide film can adapt to the outdoor environment, resist corrosion, and maintain good appearance stability.

High Humidity Environment (Such as Bathroom Hardware)

Electrophoresis process: The formed coating has high corrosion resistance and can effectively prevent the aluminum alloy from rusting in a high-humidity environment. Electroplating process: For example, chromium plating can improve the surface's corrosion resistance and glossiness, adapting to a humid environment.

High-Temperature Environment (Such as Parts of Automobile Engines)

Micro-arc oxidation process: The film layer formed by this process has good thermal shock resistance and can maintain stable performance at high temperatures. Nitriding treatment process: It has high surface hardness and can still maintain certain performance in a high-temperature environment, and is resistant to high-temperature oxidation.

High-Friction Environment (Such as Mechanical Transmission Parts)

Mechanical polishing process: It can make the surface smooth, reduce the friction coefficient, and reduce wear. Electroplating process: Such as hard chromium plating can improve the surface hardness and enhance the wear resistance.

Internal Environment of Electronic Equipment (Such as Mobile Phone Parts)

Electroless plating process: It can improve electrical conductivity, and the uniformity of the plating layer is good, which can meet the requirements of electronic parts with complex structures. Anodizing process: It has good insulating properties and can prevent problems such as short circuits between electronic components.

Conclusion

There are various surface treatment methods for aluminum alloy die casting, including anodizing, micro-arc oxidation, powder spraying, electroplating and other processes. In terms of cost, processes such as sandblasting and chemical passivation are low-cost, while processes such as micro-arc oxidation and nitriding treatment are high-cost.  In terms of performance, different processes have their own advantages in terms of wear resistance, corrosion resistance and comprehensive performance.  In terms of usage environment, powder spraying and anodizing are suitable for outdoor use;  electrophoresis and electroplating are selected for high-humidity environments;  micro-arc oxidation and nitriding treatment are used for high-temperature environments;  mechanical polishing and electroplating are suitable for high-friction environments;  and electroless plating and anodizing are preferred for the internal environment of electronic equipment.  In practice, appropriate surface treatment processes should be selected according to factors such as requirements, cost and usage environment.