How To Test The High Temperature Resistance Of Aluminum Alloy in Aerospace?

1. The Importance of Aluminum Alloy in Aerospace Applications and the Necessity of High Temperature Resistance Testing
(1) Importance
Aluminum alloys are widely used in the aerospace industry. In aircraft structures, aluminum alloy is used to manufacture components such as fuselage skin, wing beams, landing gear, etc; In rocket and satellite structures, aluminum alloy is also used to manufacture shells, brackets, etc. The lightweight characteristics of aluminum alloy can effectively reduce the weight of aerospace vehicles, improve payload capacity, and reduce launch costs. Meanwhile, its excellent processing performance makes the manufacturing of structural components easier and can meet the design requirements of complex structures in aerospace vehicles.
(2) Necessity of testing
During the operation of aerospace vehicles, aluminum alloy structural components will face high temperature environments. For example, the combustion chamber temperature of an aircraft engine can reach thousands of degrees Celsius. Although aluminum alloys do not directly come into contact with such high temperatures, they are still subject to a certain degree of thermal radiation and conduction in certain areas. If the high temperature resistance of aluminum alloy is insufficient, it can lead to a decrease in material strength, deformation, cracking, and even melting, thereby endangering the safety of aerospace vehicles. Therefore, testing the high temperature resistance of aluminum alloys can evaluate their performance changes in high-temperature environments, providing a basis for the design and material selection of aerospace vehicles.
2. Testing method for high temperature resistance of aluminum alloys
(1) High temperature tensile test
High temperature tensile testing is a commonly used method to evaluate the mechanical properties of aluminum alloys at high temperatures. During testing, the aluminum alloy sample is placed in a high-temperature environment, subjected to uniaxial tensile load, and its stress-strain curve is measured to obtain mechanical performance parameters such as yield strength, tensile strength, and elongation. This test can simulate the stress situation of aluminum alloys at high temperatures and evaluate their deformation and fracture characteristics at high temperatures.
(2) High temperature creep test
High temperature creep testing is the study of the deformation behavior of aluminum alloys under high temperature and long-term loading. At high temperatures, aluminum alloys undergo slow plastic deformation, known as creep. Through high-temperature creep testing, parameters such as creep rate and creep limit of aluminum alloys under different temperature and stress conditions can be measured to evaluate their long-term stability at high temperatures.
(3) Thermal cycle test
Thermal cycling testing simulates the temperature changes experienced by aluminum alloys in aerospace vehicles. Heat and cool the aluminum alloy sample in a cyclic manner between high and low temperatures, and observe its performance changes, such as dimensional stability and changes in mechanical properties. This test can evaluate the fatigue performance and reliability of aluminum alloys under temperature cycling.
(4) Oxidation test
Under high temperature conditions, oxidation reactions occur on the surface of aluminum alloys, forming oxide films. The performance of oxide film has a significant impact on the high temperature resistance of aluminum alloy. Oxidation testing can evaluate the oxidation rate of aluminum alloys at high temperatures, the structure and properties of oxide films, and understand the impact of oxidation on the mechanical properties and corrosion resistance of aluminum alloys.
3. Testing standards and equipment
(1) Testing standards
At present, there are multiple relevant standards for testing the high temperature resistance of aluminum alloys, such as GB/T 228.2-2015 "Tensile Testing of Metallic Materials Part 2: High Temperature Test Methods" and GB/T 2039-2012 "Tensile Creep and Endurance Test Methods for Metals". These standards specify requirements for testing methods, sample preparation, testing conditions, data processing, and other aspects to ensure the accuracy and comparability of test results.
(2) Instrument and equipment
High and low temperature tensile testing machine: used for conducting high temperature tensile testing, capable of applying tensile load to the specimen in a high temperature environment and measuring force values and displacements.
High temperature furnace: provides a high-temperature environment for testing, usually with a precise temperature control system that can stably raise the temperature to the set temperature and maintain a constant temperature.
Streptometer: a strain measurement system used to measure the strain of a specimen during tensile testing, which can be installed on the specimen and connected to a testing machine.
Creep testing machine: specifically designed for high-temperature creep testing, capable of applying a constant load and measuring the deformation of the specimen over time.
Thermal cycle test chamber: It can achieve high and low temperature cyclic heating and cooling, simulating the temperature change environment of aluminum alloy in aerospace vehicles.
4. Preparation of test samples and testing process
(1) Sample preparation
Cut standard sized specimens from aluminum alloy materials, usually dumbbell shaped specimens, with specific dimensions determined according to relevant standards. Clean the surface of the sample, remove oil stains and impurities, and ensure that the sample surface is flat and undamaged. For some special tests, such as oxidation testing, it may be necessary to perform special surface treatments on the sample, such as grinding, polishing, etc.
(2) Testing process
Equipment inspection and calibration: Check whether the electrical system, mechanical components, and control system of the testing equipment are operating normally, calibrate force and displacement sensors to ensure measurement accuracy.
Sample installation: Install the sample in the corresponding fixture, ensuring that the clamping is firm and the axis of the sample is consistent with the tensile direction. If an extensometer is used, install it on the specimen and connect it to the strain measurement system of the testing machine.
Set testing conditions: Set parameters such as high temperature environment temperature and loading rate according to testing requirements. For example, in high-temperature tensile testing, the test temperature can be set to 150 ℃, 200 ℃, etc., and the loading rate is usually 10mm/min.
Start testing: Start the testing equipment, heat the sample to the set temperature, and maintain a constant temperature for a certain period of time to ensure that the sample temperature is uniform. Then apply tensile load or perform other testing operations, and record real-time data such as force values, displacement, strain, etc.
Data processing and analysis: After the test is completed, calculate the mechanical performance indicators of the material based on the recorded data, such as yield strength, tensile strength, elongation, etc. Analyze stress-strain curves, creep curves, etc. to evaluate the high temperature resistance of aluminum alloys.
5. Factors affecting the high temperature resistance of aluminum alloys
(1) Alloy composition
Different series of aluminum alloys have different high temperature resistance properties. For example, 2000 series aluminum alloys (such as 2024, 2017, etc.) have high strength and hardness, and are commonly used in the aerospace and defense fields. Their heat resistance temperature is generally between 200 ℃ and 300 ℃; The 7000 series aluminum alloys (such as 7075, 7050, etc.) belong to high-strength aluminum alloys with extremely high strength and good heat resistance. They are mainly used in the aerospace and military fields, and their heat resistance temperature is generally between 350 ℃ and 450 ℃. The content and proportion of copper, magnesium, zinc and other elements in alloys can affect the microstructure and properties of aluminum alloys, thereby affecting their high temperature resistance.
(2) Microstructure
The microstructure of aluminum alloys, such as grain size, phase composition, and distribution of precipitated phases, has a significant impact on their high temperature resistance. Fine grains can enhance the strength and toughness of aluminum alloys, and improve their high-temperature resistance; Reasonable phase composition and precipitation phase distribution can enhance the strength and stability of aluminum alloys, and improve their high temperature resistance.
(3) Processing technology
Different processing techniques, such as casting, extrusion, forging, mechanical processing, etc., can affect the microstructure and properties of aluminum alloys, thereby affecting their high temperature resistance. For example, defects such as shrinkage and porosity in casting processes can reduce the strength and toughness of materials; Heat treatment process can change the microstructure of aluminum alloy and improve its high temperature resistance.