Salt Spray Test in Die Casting: Everything You Need to Know

If your die-cast parts face harsh outdoor environments or acidic and alkaline conditions, corrosion resistance is vital for long-term safety. Salt spray testing is a popular method to evaluate the corrosion-resistant capability of the material or coating. In the following article, you can learn more about the knowledge of salt spray testing in die casting.

What Is the Salt Spray Test in Die Casting?

When it comes to the quality control method of die casting parts, it is inevitable to test their performance. Whether for decorative or functional purposes, corrosion resistance is an essential property that die casting components must possess. 

Salt spray testing is a test that evaluates the corrosion resistance of casting materials or surface coatings. The results of salt spray testing provide reliable reference indicators.

Generally, salt spray testing employs two methods. 

The first involves exposing samples to natural environments, which most closely mimics actual corrosion conditions but requires extended testing periods. 

The second method utilizes accelerated corrosion simulation through artificial salt spray testing. This artificial corrosion environment requires placing test samples in a sodium chloride solution of a specific concentration. In most cases, this solution consists of a 5% sodium chloride solution maintained at 35°C.

Why Salt Spray Testing Is Crucial in Die Casting?

It is easy to understand why salt spray testing is important in die casting:

First, corrosion impacts not only the appearance but also the properties of die casting parts. 

Second, it helps verify the effectiveness of protective coatings. 

Third, it ensures the components meet required quality standards. 

Below, you’ll find a detailed explanation of its importance.

Identifying the Hazards of Corrosion

Although aluminum—the most widely used metal in die casting—naturally develops an oxide layer for protection, this layer can still be corroded after long-term exposure to humid, saltwater, or salt spray environments. 

If your die-cast parts are used in marine equipment, automotive components, or solar panel enclosures—where harsh conditions are unavoidable—salt spray testing helps reveal how quickly corrosion can cause serious damage. Such damage not only affects appearance but also weakens the mechanical strength of the parts.

Testing the Corrosion Resistance of Coatings

To make die-cast components last longer, we usually add surface treatments that boost their corrosion resistance. Since no two coatings perform the same, salt spray testing helps us simulate harsh environments and quickly see how well they hold up.

This allows you to see how well each coating performs under real-world conditions—helping you choose the most suitable one for your die-cast parts.

Ensuring Reliable Quality

Whether in the automotive, marine, or telecommunications industries, corrosion resistance requirements for die-cast components are governed by specific standards. These standards serve as benchmarks for evaluating whether die-casting manufacturers meet customer quality demands. 

With salt spray testing, every component goes through a tough performance check. This way, you can be confident it meets industry corrosion resistance standards and delivers reliable quality before it leaves the factory.

What Parameters Affect the Salt Spray Test?

During salt spray testing, you need to keep a close eye on key factors such as pH level, solution composition, and temperature. Even small adjustments to these settings can greatly influence both the test duration and the final results.

PH Levels

For salt spray testing, the pH level of the solution should be kept between 6.5 and 7.2. Keeping the pH level at this neutral range helps avoid unwanted effects on the corrosion process that can occur if the solution is too acidic or too alkaline.

Solution Composition

In most cases, salt spray testing is carried out with a 5% sodium chloride solution prepared in deionized water. Using this standard mixture is what defines a Neutral Salt Spray Test (NSS).

By adding acetic acid, the environment becomes more acidic—making the acetic acid salt spray test (AASS) ideal for evaluating decorative chrome plating on zinc die-cast components.

If acetic acid is first added and then copper chloride is introduced, the process speeds up pitting and corrosion on metal coatings.

This solution is suitable for testing the corrosion resistance of electroplated coatings on your die-cast parts and the corrosion resistance of aluminum alloys. This enhanced method is known as the Copper Accelerated Acetic Acid Salt Spray Test, or simply CASS.

Temperature

The temperature for salt spray testing is maintained at 35 ℃ (95℉). This constant-temperature environment accelerates the corrosion rate, enabling faster evaluation of die-cast components’ resistance to corrosion.

Time

The test duration can be flexibly adjusted. The length of the test period depends on your specific requirements for the corrosion resistance of the die-cast parts. 

If only basic corrosion resistance is needed, a test duration of 24 to 72 hours is sufficient. 

However, if the parts must withstand prolonged exposure to outdoor corrosive environments without damage, the test duration can be extended up to 1000 hours.

The Procedure of Salt Spray Testing

In this part, we’ll walk through the steps of how salt spray testing is carried out. While adjustments may be necessary during actual implementation, the general procedure is as follows:

#1 Sample Preparation

Before commencing the salt spray test, the die-cast samples to be tested must be cleaned. In this process, you need to ensure there is no oil or dust on the casting part’s surface. Because the adhering impurities can affect the test results. Testing can be performed regardless of whether your die-cast parts have a surface coating.

#2 Solution Preparation

Start by mixing a 5% sodium chloride solution with deionized water. Then, adjust its pH to fall within the neutral range of 6.5–7.2. If performing AASS or CASS, add an appropriate amount of acetic acid or copper chloride to the solution.

#3 Preparation of the Salt Spray Chamber

The temperature of the salt spray chamber must be set to 35 ℃ (95 ℉). Simultaneously, ensure the spray system is functioning properly and set the test duration.

#4 Test Procedure

During salt spray testing, the solution must be atomized using a spray nozzle and evenly applied to the surface of the die-cast part. The part is then continuously exposed to the atomized environment until the preset test duration concludes. The salt spray chamber must remain sealed throughout the entire process to maintain a stable test environment.

#5 Post-Test Analysis

Once the exposure time is up, the test engineer will remove the samples from the chamber and evaluate the extent of corrosion. Typical reference indicators include the percentage of affected area, the corrosion rate, and mass (weight) loss.

Based on these results, the engineer prepares a report detailing the corrosion resistance of the casting material or its surface coating.

The Standard of Salt Spray Test

Depending on the requirements of different countries, regions, and industry organizations, there are numerous standards for salt spray testing. In the following article, I will introduce the three most common ones.

ISO 9227

ISO 9227 is the internationally recognized standard for salt spray testing. This standard is suitable for salt spray testing in artificial atmospheric environments. It specifies the whole procedure of salt spray testing, including:

• Requirements for test equipment
• Preparation of test samples
• Properties of the salt solution
• Methods for evaluating salt spray test results

ASTM B117

ASTM B117 is a standard published by ASTM International and is the longest-standing standard for salt spray testing. 

This standard establishes standardized procedures for operating salt spray testing equipment. 

It also provides reference information on the relative resistance to corrosion of metals and coated metals when exposed to a standardized corrosive environment.

ASTM G85

ASTM G85 is also a testing standard published by ASTM International. 

This standard specifies modified salt spray test specifications (such as AASS and CASS) based on ASTM B117. 

It is frequently referenced in industries including automotive, aerospace, and electronics.

Industries Suitable for Salt Spray Testing

Many industries that require components produced via die casting must meet salt spray test standards. The following article lists some industries suitable for salt spray testing.

Automotive Industry

Each year, nearly 60% of die-casting parts are supplied to the automotive industry. Not only aluminum die-cast engine blocks and transmission housings, but also chassis components, body panels, and trim parts require corrosion protection to withstand their operating environments. 

Corrosion threats include moisture exposure, road salt, and chloride ion damage from galvanic corrosion. If your vehicle’s structural components corrode, their strength will be compromised and may lead to functional failure. And if your seals corrode, leaks are likely to follow—posing safety risks.

Therefore, any professional die-casting manufacturer will ensure that automotive die-cast components meet the ASTM B117 and ISO 9227 standards for salt spray testing.

Marine Industry

For the marine industry, corrosion-resistant die-casting equipment housings and components are essential. Vessels must operate continuously at sea, with hulls directly exposed to seawater corrosion. Offshore structures and casting marine parts also endure harsh saltwater environments when subjected to waves or rain. 

Salt spray corrosion testing is crucial for ensuring the reliable operation of marine equipment in saline conditions.

Aerospace Industry

Whether in the atmosphere, at coastal airports, or along low-altitude maritime routes, these environments can cause corrosion to aviation equipment.

Salt spray testing of die-cast components in the aerospace industry is conducted to determine how long these parts can maintain structural integrity during service. 

This provides valuable reference for equipment maintenance and component replacement, ensuring the operational safety of aviation equipment.

The Advantages and Disadvantages of Salt Spray Testing

As a performance testing method, salt spray testing has its advantages as well as limitations. Die casting manufacturers with rigorous quality control will take all of these factors into account.

Advantages

• Standardized Testing

Salt spray testing creates a stable, standardized environment that simulates harsh conditions, allowing die-cast parts to be thoroughly evaluated for corrosion resistance. With this method, you can clearly see how different materials or coatings perform, making it easier to choose the best solution for long-lasting protection.

• Rapid Test Results

Compared with evaluating corrosion resistance in natural environments, salt spray testing speeds up the process by controlling specific parameters, allowing results to be obtained much faster. This means you can assess performance in less time and bring your products to market sooner.

Disadvantages

• Limited Test Environment

Salt spray testing is carried out in a chamber, and while the environment is standardized, it inevitably differs from real-world conditions. 

In addition, the chamber size is limited. For large or heavy die casting parts, it may not be possible to test the entire part at once. In such cases, representative samples are typically selected for testing.

Conclusion

By now, you should have a clear view of salt spray testing—its definition, process, key factors, and applicable industries. If you need a die casting manufacturer to run standard or modified salt spray tests, feel free to contact Sunrise. We deliver precise, comprehensive test reports for your die-cast parts.