Heat Treatment of Aluminum Alloys
Heat treatment code of aluminum alloy
|
Nicknames |
Name |
Meaning |
Characteristics |
|
F |
free processing state |
Directly used for machining without work hardening or heat treatment. |
Variable properties, adaptable to a variety of processing conditions. |
|
O |
Annealed condition |
Fully annealed to the minimum strength condition |
Suitable for products requiring high ductility, such as deep-drawn parts. |
|
H |
Work-hardened condition |
Cold work hardening, may be partially annealed |
Can be subdivided into H1 H2 H3 H4. Adjustment of hardness and properties. |
|
W |
Solution heat-treated condition |
Natural aging is not completed after solid solution treatment, properties change with time. |
Alloys for natural ageing strengthening |
|
T1 |
High temperature molding + natural aging |
High temperature molding followed by natural cooling and aging |
Improved properties by natural aging |
|
T3 |
Solution treatment + cold working + natural aging |
Solid solution treatment followed by cold working and natural aging |
Improvement of hardness and strength |
|
T4 |
Solid solution treatment + natural aging |
Solid solution treatment followed by natural aging |
Increased ductility and medium strength
|
|
T5 |
High temperature molding + artificial aging |
High-temperature molding followed by cooling and artificial aging |
Strengthening hardness and resistance
|
|
T6 |
Solution treatment + artificial aging |
Artificial aging after solid solution treatment |
Provides high strength and good mechanical properties
|
|
T7 |
Solution treatment + aging |
Stabilized by solid solution treatment followed by over-aging |
Reduce hardness and increase stress corrosion resistance
|
|
T8 |
solution treatment + cold working + artificial aging |
Cold working after solid solution treatment followed by artificial aging |
Balance strength and toughness |
|
T9 |
National solution treatment + artificial aging + cold working |
Cold working after artificial aging |
Improve molding performance and final hardness |
|
T1O |
High temperature forming + cold working + artificial aging |
Cooling, cold working and artificial aging after high temperature molding |
Enhanced hardness by composite process |
Heat treatment process of aluminum alloy
The heat treatment processes of aluminum alloys mainly include the following:
1.Annealing
Purpose: To reduce hardness, eliminate internal stress, and improve plasticity and processing properties.
Process: Aluminum alloy is heated to a specific temperature (usually between 300°C and 500°C), held for a certain period of time and then slowly cooled.
Application: Suitable for improving the formability and processing properties of aluminum alloys.
2.Solution treatment
Purpose: To dissolve alloying elements uniformly in the aluminum matrix to prepare for aging treatment.
Process: The aluminum alloy is heated to a higher solution temperature (about 450°C to 550°C), maintained for a period of time, and then rapidly cooled (such as water cooling).
Effect: Improve the plasticity and ductility of materials.
3.Aging treatment
It is divided into: natural aging and artificial aging.
Purpose: To promote the precipitation of alloy elements into strengthening phases in the aluminum matrix and improve the strength and hardness of the material.
Natural aging: carried out at room temperature and takes a longer time.
Artificial aging: heating at a moderate temperature (about 100°C to 200°C) and keeping warm for several hours to dozens of hours.
Effect: Significantly improve the mechanical properties of aluminum alloy.
4.Quenching
Purpose: Rapid cooling to maintain the solid solution structure and prevent element precipitation.
Process: Rapidly cool the aluminum alloy after solution treatment, usually using water or oil cooling.
Application: Maintain high strength and good plasticity of materials.
5.Normalizing(not commonly used for aluminum alloys)
Features: Similar to annealing, but cooling speed is slightly faster.
Effect: Refine the grains and improve the mechanical properties of the material.
6.Tempering
Purpose: To eliminate the stress caused by quenching and improve toughness.
Process: After quenching, the aluminum alloy is heated to a lower temperature, kept for a period of time and then cooled.
Effect: Maintain the hardness of the material and improve toughness.
The heat treatment process of aluminum alloy includes annealing, solution treatment, aging treatment, quenching, etc. These processes can optimize the performance of the material, such as improving strength, hardness, toughness and corrosion resistance. It is very important to choose the appropriate heat treatment process according to the specific application requirements.
Common aluminum alloy heat treatment defects
1. Overheating and overburning
Reason: Due to the heating temperature being too high or the heating time being too long, the internal grains of the metal are severely coarsened, which reduces the strength and toughness of the material and makes it difficult to recover.
Measures: Strictly control heating temperature and time, ensure the use of accurate temperature control systems and regular calibration of equipment. Develop and follow standardized heat treatment process procedures.
2.Quenching cracking
Cause: Due to the quenching cooling rate being too fast or uneven, the internal stress of the aluminum alloy is too large, resulting in the generation of cracks, which is especially common in thick-walled or complex-shaped parts.
Measures: Choose appropriate cooling medium and cooling method to avoid excessive cooling speed. For parts with complex shapes or thick walls, graded quenching or preheating quenching can be used to reduce stress. Optimize the shape design of the workpiece to avoid stress concentration areas as much as possible.
3.Excessive aging
Cause: Over-aging will lead to a decrease in alloy properties, which is manifested as a decrease in strength and hardness. This often occurs when the aging time or temperature exceeds the process requirements.
Measures: Strictly follow the time and temperature requirements of aging treatment to avoid over-aging. Test and adjust process parameters to determine the best aging solution. Introduce a process monitoring system to monitor temperature and time in real time.
4.Deformation and warping
Cause: Due to temperature changes or uneven cooling during heat treatment, especially during quenching, the shape of the parts can easily be deformed or warped, affecting dimensional accuracy.
Measures: Use adequate fixtures or support devices before heat treatment to reduce deformation. Optimize the process, such as slow cooling or isothermal quenching. If necessary, perform stress relief treatment on key parts.
5.Corrosion and oxidation
Reason: High-temperature heating in an air furnace, if the humidity in the furnace is high or contains other harmful substances such as sulfides, will aggravate the high-temperature oxidation of aluminum products.
Characteristics: Bubbles form on the metal surface or cavities form inside the metal.
Measures: Use protective atmosphere such as nitrogen or argon during heat treatment, or use vacuum heat treatment equipment to prevent oxidation. Ensure the surface of the workpiece is clean and remove impurities and oil. Clean or treat the surface quickly after heat treatment to prevent oxidation.