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Surface Finishing Guide for Aluminum Die Casting

Aluminum die casting is widely popular in many industries due to their excellent mechanical properties. They offer impeccable quality, performance, durability, and strength-to-weight ratio. All modern die-casting parts require specific surface finish, coating, polish, or paint to achieve desired effects.

In most die-cast products, surface treatment is not necessarily aesthetically focused. Aluminum die-cast parts often require various surface treatments to enhance their performance in certain applications.

Advantages of Surface Finishing

Providing surface treatment for aluminum die castings can bring many benefits, including:

1. Corrosion Resistance

Aluminum die-casting parts have excellent corrosion resistance. However, this property may fail under water or damp conditions. Proper surface treatment of aluminum die-casting parts can minimize the roughness of the casting surface, thus improving corrosion resistance. This is particularly important for parts used outdoors.

2. Tensile Strength

Sometimes, durability alone cannot meet the requirements of products or functions. Proper surface treatment methods, such as electroplating, can improve the strength of aluminum die-casting parts. Coating stronger materials on aluminum die-casting parts can give them higher tensile tolerance.

3. Chemical Inertness

Under specific conditions, aluminum surface roughness is not inert to certain compounds. After surface treatment, the smooth surface can protect the appearance of aluminum die-casting parts from chemical corrosion, making them very suitable for use in harsh environments.

4. Pleasant Appearance

In the eyes of consumers, aluminum die-casting parts with rough surfaces often look unsightly. However, surface treatment can give them a smooth, shiny, and straightforward aesthetic appearance, which is particularly important for decorative or ornamental parts.

Common Surface Finishes for Aluminum Castings

Die casting manufacturers will determine the surface treatment technology to be used based on material specifications. Designers can also tell die casting manufacturers the surface effect they want to achieve, and die casting manufacturers will propose suitable material recommendations. Common surface treatment technologies include:

1. Anodizing

This electrochemical treatment process is suitable for common non-ferrous die-casting metals such as aluminum, zinc, and magnesium. It provides scratch resistance and corrosion resistance. There are three types of anodized aluminum finish:

Type I – This type uses chromic acid to form the thinnest anodized oxide coating (minimum 0.0001 inches). This allows the die casting parts to have slight dyeing ability and high corrosion resistance.
Type II – It involves the use of sulfuric acid to generate a thicker oxide coating (0.0001 inches to 0.002 inches). The die casting parts have high dyeing ability and excellent corrosion resistance.
Type III – It also uses sulfuric acid like Type II, but adds high electric current. The thicker oxide layer (over 0.001 inches) results in corrosion resistance and abrasion resistance of die casting parts.

2. Electroplating

This protective finishing method is suitable for almost all die-casting aluminum surface treatments. The castings are immersed in a solution containing metal ions for electroplating of aluminum castings. After passing through an electrolytic device, a thin metal film will form on the surface of the aluminum casting.

Cadmium plating and zinc plating are very popular choices for most aluminum die-castings. However, for some specific specifications, other metals may also be used. Electroplating treatment improves the functionality and aesthetics of aluminum castings, making them applicable to many complex, large, and customized aluminum products.

3. Polishing

This process is mainly done manually. It is necessary to use abrasive materials to produce a glossy and shiny effect. There are various polishing methods that can be used to create a mirror-like bright appearance, including subsequent steps such as rough grinding, polishing, brightening, and surface protection.

4. Powder Coating

The application of dry powder is very common in commercial aluminum products. After proper pretreatment of aluminum castings, the powder is sprayed on the surface of the aluminum castings using a spray gun, and then heat is applied to solidify the powder, achieving a permanent effect.

The powder can be thermoplastic or thermosetting plastic to create a flexible finish. Thermoplastic powder is soft and has no chemical bonds, and can be reused repeatedly, so the coating can be reused. However, the thermosetting powder will form irreversible chemical bonds after heating.

5. Chrome Plating

The electrolytic setup used in this process is exactly the same as that used in electroplating. However, it specifically requires chromium in the solution to provide an electrolytic coating on the surface of the aluminum casting. A thick hard plating enhances its functionality, while a thin decorative plating has reflective properties.

Due to its abrasion resistance, anodic aluminum oxide is one of the best solutions for surface treatment of die-castings. It gives the surface a deep, rich, and attractive metal appearance without peeling off. Other options can also be determined based on factors such as cost, ease of operation, and usage.

Categories of Die Casting Surface Finish

Manufacturers may categorize the surface finish for aluminum castings into the following grades:

1. Utility Grade:

Only protective functions are provided for hidden or invisible surfaces, without any decorative functions. This grade hardly focuses on surface defects.

2. Functional Grade:

The surface may be sprayed with a decorative coating. Spot-polish or simple painting at this grade is usually used to repair surface defects.

3. Commercial Grade:

Surface treatment at this grade mainly focuses on aesthetics, defect elimination, and protection of die castings. This grade is mainly used for high-stress structural projects.

4. Consumer Grade:

Surface treatment is mainly decorative. Defects on the coating surface should be minimized.

5. Superior Grade:

This grade involves alloy coatings that need to be used in specific fields.

General Process of Aluminum Die Casting Finish
Step #01: Thoroughly clean the surface

Any contaminants, such as oil, grease, or dirt, may affect the adhesion and quality of the coating. Therefore, the surface must be cleaned before surface treatment. The surface may also need pretreatment, such as sandblasting or grinding, to ensure it is smooth and free of defects.

Step #02: Choose the appropriate finishing method

The choice of the finishing method depends on many factors, including functionality, aesthetics, environmental factors, and cost. The selected method should have the required performance, such as corrosion resistance, durability, and visual appeal.

Step #03: Quality control and inspection

Monitoring the quality of the surface finish throughout the process is crucial to ensure it meets the required specifications. This involves using appropriate measuring and testing equipment and adhering to industry standards for surface finish quality.

Daye Diecasting promises to meet your needs for aluminum die castings in every crucial aspect. Our expert team is always ready to provide the best surface treatment for your products. Please feel free to contact us and specify your requirements for the surface treatment of aluminum die castings.

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