All About Tensile Testing in Die Casting

Whether it’s automotive chassis or aircraft landing gear, these die-casting components are subjected to vibration and prolonged fatigue loads in real-world applications, requiring exceptional tensile strength to prevent fractures that could pose safety hazards. If you wish to learn about tensile testing in die-casting performance testing, the following article will be beneficial.

What Is Tensile Testing？

Tensile testing is a type of mechanical strength test and one of the most common techniques for evaluating the mechanical properties of materials. 

In tensile testing, the test equipment will apply increasing stress to a tensile sample(with known length and cross-sectional area), and the response of the sample will be measured to calculate the ability of the material that support a stress. 

Through tensile testing, you can obtain many useful mechanical property parameters, such as yield strength, ultimate tensile strength, ductility, strain-hardening characteristics, and modulus of elasticity. These property parameters will influence your choice of materials used in different applications.

Tensile testing can be applied to a wide variety of materials, including metals, rubber, plastics, ceramics, and more. In the context of die-cast component performance testing, it typically refers specifically to testing metals. 

In other words, the purpose of tensile testing is to determine the working load limits of metals and alloys, thereby enabling the selection of suitable manufacturing materials for die-cast components intended for specific applications.

What Is the Procedure of Tensile Testing？

While the implementation of tensile tests on different materials may vary in detail, the overall process remains largely consistent. The following section will provide a detailed overview of the tensile testing procedure for die-cast components.

Sample Preparation for Die Castings

• The Selection of Samples

For tensile testing of die-cast components, the first step involves sample preparation. 

There are two options for selecting test specimens. 

The first involves sampling from specific locations on the entire die-cast part. This method is more commonly used because the size limitations of tensile testing equipment make it impractical to test the entire part. 

However, sampling locations must comply with international standards ISO 6892-1 and ASTM E8/E8M. 

The alternative is to test the entire component, which is generally feasible only for small die-cast parts.

• The Shape of Samples

The tensile testing samples are commonly shaped like a “dogbone”. The ends of the sample are thicker, which is suitable for gripping. This kind of sample often has a round or square standard cross-section. The central portion(called the gauge section) is reduced in width, so it can be subjected to the maximum stress. The gauge length is either 2 inches, 80 mm, or 50 mm.

Preparation of Test Equipment and Parameters

• Equipment

The tensile testing is performed on a universal testing machine or a dynamic fatigue testing system. Sometimes, a miniaturized specimen test device is needed. At this stage, the testing equipment requires calibration and debugging to ensure the tensile test can proceed smoothly.

• Accessories

On the testing equipment, there are certain components that cannot be overlooked, as they perform critical functions.

Grips: Grips are attachments used to secure test specimens. They need to be correctly arranged before the test begins.

Load cells: Load cells are installed on the equipment to measure force.

Extensometers: Extensometers are independent sensors used to measure strain accurately.

• Temperature

In most cases, tensile tests are conducted at ambient temperature. 

Occasionally, they are performed at elevated temperatures when die-cast components are intended for boiler and pressure vessel applications.

Implementation of Tensile Strength Testing

During tensile testing, the testing machine applies a continuously increasing tensile force to the specimen’s longitudinal axis. This stretching must be performed at a standardized speed. 

The specimen generates a counterforce to resist elongation. Initially, the deformation exhibits elastic behavior, meaning the specimen springs to its original length once the external force is removed. 

However, as stress increases, permanent deformation (plastic deformation) occurs, indicating the specimen cannot fully recover its original form even after the external force is withdrawn. It gets longer and thinner.

Finally, the tested sample could no longer withstand the progressively increasing force. A neck begins to form and the sample fractures there. Once the sample fails completely, the testing equipment will cease to apply any further force.

Data Collection and Calculations

During testing, the elongation and force data of the sample are recorded by the testing machine and plotted as a stress-strain curve. This curve reflects how the material responds to the applied force. It can also reflect the yield strength, elongation, and elastic modulus.

The load cell provides data on the maximum load, which is the key data for calculating tensile strength. With the maximum load and the original cross-sectional area of the specimen, the tensile strength can be derived using the formula.

Post-Test Inspection and Reporting

After the test concludes, the testing personnel will examine the fractured specimen to gather additional information required for the report. 

Finally, a mechanical properties report will be generated for this specimen, including but not limited to yield strength, ultimate tensile strength, elastic modulus, ductility, and other relevant data.

Why and When Tensile Testing Is Needed In Die Casting？

You might wonder why tensile testing is so crucial in evaluating the performance of die-cast components. And at what stage of the die-casting process is tensile testing typically employed? Here’s the explanation.

Why Tensile Testing Is Needed in Die Casting

• Selecting the Right Application Materials

Not only do aluminum, magnesium, and zinc alloys exhibit significant differences in mechanical properties, but even various aluminum alloys differ in ductility, tensile strength, and yield strength. 

This variation stems from differing silicon, copper, and manganese content within the alloys. 

To ensure die-cast components for diverse applications are matched with the most suitable casting alloy, tensile testing results provide highly valuable reference data.

• Assisting in Improving Die Casting Processes

Changes in the mechanical properties of raw materials following a series of die casting processes are to be expected. 

For instance, the injection process can introduce defects such as porosity and looseness within castings, leading to a decline in mechanical performance. Additionally, heat treatment or alterations in the composition of die casting materials can also affect tensile properties. 

Testing the tensile properties of die castings provides insight into how the die casting process impacts materials, thereby guiding the optimization of the die casting process.

• Supporting Design Engineering

Conducting tensile tests on die-casting materials enables die-casting engineers to predict component behavior during part design. For instance, it can determine the load at which fracture occurs, whether plastic deformation will develop, and whether strength will deteriorate under high temperatures.

• Ensuring Materials Meet Specific Specifications or Standards

Certain industries impose specific tensile strength requirements on the mechanical properties of die-cast components. Particularly in the automotive and aerospace sectors, load-bearing capacities for die-cast parts adhere to industry-specific standards. 

To ensure outgoing die-cast components meet these particular specifications and standards, manufacturers must conduct tensile testing.

When Tensile Testing Is Performed in Die Casting

• Process Validation

After completing the die casting mold design, you must select the appropriate casting material. Mechanical properties serve as a critical reference indicator during material selection. Therefore, tensile testing of the material is required to verify whether the chosen alloy meets the mold’s design specifications.

• First Article Inspection

During the trial production phase of die casting, it is essential to determine whether the process parameters meet the mechanical performance requirements of the die-cast parts. Therefore, sampling from these parts for tensile testing is necessary.

• Quality Control

During the mass production of die-cast components, samples are also extracted for tensile testing to ensure the stability of the final delivered die-cast components’ performance.

Conclusion

Whether during the material selection phase of die casting or in the quality inspection process of die-cast components, tensile testing serves as a critical step in ensuring the quality of die-cast parts meets industry standards. If you’re looking for a die-casting manufacturer with strict quality control, please feel free to contact Sunrise.