Aluminum die casting, known for its lightweight and high-precision molding capabilities, is utilized in a wide range of fields, including automobiles, home appliances, building materials, and precision equipment. The most frequently used material, “ADC12,” offers excellent castability and dimensional accuracy but has the drawback of poor corrosion resistance.

ADC12 contains a high amount of silicon to improve its castability, but this also leads to the generation of white rust, a cause of corrosion, and increases the difficulty of surface treatment. For example, in processes like painting and anodizing, achieving a uniform film is challenging, and issues such as unevenness and poor adhesion are common depending on the product.

Due to these factors, applying surface treatment is considered almost essential for aluminum die-cast products.

The main objectives for applying surface treatment are the following three points:

In harsh environments such as outdoors, coastal areas, or chemical plants, the untreated surface of aluminum die casting will corrode quickly. Appropriate surface treatment can protect the product from oxidation and corrosion, significantly extending its service life.

For automotive parts and products where design is important, the beauty and texture of the surface directly influence purchasing decisions. Techniques like chrome plating and powder coating can provide a luxurious finish and a variety of color options.

Depending on the application, properties such as electrical insulation, conductivity, wear resistance, or heat resistance may be required. To meet these needs, treatments like hard anodizing or special plating are used.

To achieve these objectives, it is necessary to select a surface treatment that matches the product’s usage environment, structural characteristics, and required performance. Furthermore, since the choice of treatment significantly affects the product cost, a cost-effective treatment strategy is crucial.

This article organizes various surface treatment technologies suitable for aluminum die casting by objective and provides a detailed explanation, including cost estimates and points to consider during selection.

A wide variety of surface treatments are applied to aluminum die-cast products depending on their purpose and application. The following section explains the features and selection points for five representative technologies.

Chemical conversion coating is a method that forms a film on the metal surface through a chemical reaction to improve corrosion resistance and paint adhesion. Representative examples include chromate treatment (hexavalent/trivalent) and non-chrome treatment.

Anodizing (anodic oxidation) is a process that forms an oxide film on the aluminum surface to enhance its corrosion and wear resistance.

While ADC12 is considered difficult to treat due to its high silicon content, it can be implemented by optimizing the processing conditions.

Plating is a process that forms a metal film on a metal surface by electrodeposition or chemical reaction.

For plating on aluminum, the presence of pretreatment (copper/nickel) significantly affects adhesion.

Selection is based on considering “functionality,” “aesthetic appeal,” and “cost” for each application.

Painting is widely used to improve the appearance quality and prevent corrosion of products.

To enhance adhesion, the precision of pretreatment, such as degreasing and chemical conversion coating, is crucial.

Physical treatments are used for deburring, adding gloss, or as a pretreatment.

These are most effective when combined with other surface treatments rather than used alone.

These surface treatment technologies must be used selectively according to the objective, cost, and product structure. The next chapter will detail how to choose these technologies based on “application.”

The applications for aluminum die-cast products are diverse, and the required functions and performance vary greatly by objective. The following section compares surface treatment technologies for four representative objectives and clarifies the reasons for their selection.

For aluminum die casting used in salt-damage areas, chemical plants, and outdoor structures, resistance to corrosion is the top priority.

For highly visible parts, appearance, color tone, and gloss are important.

When stability of gloss and color, and reproducibility in mass production are required, selecting a supplier with capable facilities is also important.

For applications involving high loads or repeated sliding, surface hardness and wear resistance are required.

These are introduced as treatments that can maintain performance even in extreme environments in industrial machinery and aircraft parts.

In recent years, there has been an increase in surface treatments that add functionality. The following are some examples:

These are gaining attention not just for traditional “protection/decoration” but as key elements in turning components into functional parts.

Thus, by selecting the optimal treatment for each application, it becomes possible to optimize performance, appearance, and cost. The next chapter will provide a detailed explanation of the cost estimates and a comparison table for each of these technologies.

The cost of surface treatment for aluminum die casting varies greatly depending on the type of treatment, the shape and size of the product, quality requirements, and the processing lot size. However, having a general sense of the market rates can help prevent excessive costs from over-specification and risks from insufficient quality.

Below is a guide to typical unit prices for common treatments (note: these are estimates and can vary based on conditions).

The above prices are for reference only. Actual quotes will vary significantly based on the supplier, quantity, and specifications.

High-performance treatments are naturally more expensive, but since they directly impact product lifespan and quality stability, they can ultimately lead to cost savings.

In a case involving electronic equipment housing parts that used “liquid coating + chemical conversion,” issues with paint peeling and conductivity problems occurred. By switching to electroless nickel plating, the defect rate dropped by 70%, and re-processing costs were eliminated. In total, a cost reduction of over 30% was achieved.

Surface treatment cost is not just an expense but a critical factor that influences the “reliability,” “aesthetic appeal,” and “added value” of a product. The next chapter will discuss specific points to consider for aluminum die casting and how to avoid treatment-related problems.

Aluminum die-cast products, especially those made from the mainstream material “ADC12,” have unique constraints and challenges during surface treatment compared to other aluminum materials. Failure to understand these in advance can lead to increased defect rates and higher costs.

To enhance castability, ADC12 contains 9.6% to 12.0% silicon. This silicon causes the following processing issues:

Defects unique to die casting, such as “porosity,” “pinholes,” and “air bubbles,” near the surface can cause the following problems:

To prevent these, it is recommended to prepare the surface with shot blasting or barrel polishing and then conduct non-destructive testing or penetrant inspection beforehand.

Hexavalent chromium chemical conversion and chrome plating, which were traditionally used, are now restricted or banned under regulations like the EU’s RoHS and REACH.

The following alternative technologies are now mainstream:

These alternative technologies not only comply with environmental regulations but also lead to improved worker safety and reduced wastewater treatment costs.

For surface treatment on aluminum die casting, selection must be based not only on “material,” “shape,” and “application,” but also on these constraints derived from the material and external factors (environmental regulations). The next chapter will introduce success and failure stories based on these points to provide practical hints.

A precision machinery manufacturer at a base in Vietnam traditionally applied only paint to its aluminum die-cast cover parts. However, in the hot and humid factory environment, corrosion progressed, leading to a serious problem where the annual replacement rate exceeded 20%.

They decided to apply hard anodizing + sealing treatment to the ADC12. Although the initial cost increased, after implementation, part failures due to corrosion became virtually zero.

As a result, they succeeded in reducing total costs, including maintenance and parts inventory, by approximately 35%. This also led to an extension of the product warranty period and a sharp decrease in customer complaints.

A domestic home appliance manufacturer mass-produced a front panel made of ADC12 with a powder coating to achieve a high-end look. However, within six months of shipment, lifting and peeling of the paint film occurred frequently. The situation ultimately led to a market recall.

An analysis of the cause revealed that the chemical conversion process had been omitted and that the surface roughness, including casting porosity, was poorly managed. As a corrective measure, shot blasting + trivalent chromium chemical conversion was added as a pretreatment, significantly improving paint adhesion.

This case is a classic example of how prioritizing process shortening and cost reduction can, in turn, lead to significant losses.

Aluminum die-cast materials like ADC12 contain a high amount of silicon, and this component hinders the formation of the anodized film. As a result, the film may become thin or develop color unevenness.

As a countermeasure, it is important to prepare the surface by polishing or shot blasting and then set the appropriate processing conditions (voltage, time).

Hard anodizing and hard chrome plating are effective in increasing wear resistance and strength, but they can cost 2-3 times more than normal treatment, at several yen per cm².

However, in many cases, the product lifespan can be more than doubled, and the cost can be fully recovered through reductions in repair/replacement costs and trouble-shooting expenses.

To judge the cost-effectiveness, the perspective of Life Cycle Cost (LCC) is important.

Hexavalent chromium and lead-based treatments are restricted or banned by environmental regulations, and trivalent chromium or non-chrome chemical conversion treatments have been introduced as alternatives. These tend to have a slightly higher initial cost, but they lead to reductions in wastewater treatment and safety management costs, and as a result, the total cost often decreases.

They are also advantageous for meeting environmental certification requests from business partners (such as ISO 14001).

Surface treatment for aluminum die-cast products is not just a “finishing” process but a strategic element that determines the product’s value.

Especially for materials like ADC12, which have excellent castability but also many constraints, an incorrect choice of treatment can lead to performance defects, increased costs, and brand damage.

When selecting a treatment technology, it is important to be mindful of the following three points:

The optimal choice is derived by collaborating with suppliers from the initial stages of product design and repeating verification and comparison.

A long-term surface treatment strategy that is not just “cheap and shoddy” is the key that will determine the competitiveness of aluminum die-cast products.

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