Age hardening, also known as precipitation hardening, is a heat treatment process used to enhance the strength and hardness of certain alloys, particularly stainless steels, nickel-based alloys, and aluminum.
This process is especially valuable for springs and wire forms that require high strength and durability for demanding applications in aerospace, medical, and industrial settings.
At Western Spring Manufacturing, age hardening is used to strengthen custom springs and wire forms, providing improved resistance to wear, deformation, and stress. This treatment is ideal for applications where components are exposed to high loads, cyclic stress, and elevated temperatures.
To learn more about advanced treatment methods, visit The Art of Crafting Precision Coil Springs and Wire Forms.
Age Hardening Process and Methods
The age hardening process involves three main stages: solution treatment, quenching, and aging.
- Solution Treatment: The alloy is heated to a high temperature, dissolving specific elements into a solid solution.
- Quenching: The alloy is rapidly cooled to lock the elements in place, preventing them from forming into separate phases and preparing the material for hardening.
- Aging: The alloy is reheated to a moderate temperature, allowing the dissolved elements to precipitate out, forming small particles that strengthen the metal. The aging process can be done naturally at room temperature (natural aging) or at elevated temperatures (artificial aging) to accelerate the effect.
Age Hardening Properties and Characteristics
Age hardening significantly improves the mechanical properties of metals, especially in terms of strength, hardness, and resistance to deformation. Key properties enhanced by age hardening include:
- Increased Hardness: The process creates a dense structure of fine particles that strengthen the metal, resulting in increased surface hardness.
- Improved Tensile and Yield Strength: Age-hardened metals are better able to withstand high loads without deforming, making them suitable for applications requiring long-term durability.
- Enhanced Fatigue Resistance: By reducing the likelihood of deformation under cyclic loads, age hardening improves fatigue life, allowing springs and wire forms to endure repeated stress cycles.
Mechanical properties improved by age hardening include:
- Hardness: Enhanced surface hardness helps prevent wear in high-friction or impact applications.
- Tensile and Yield Strength: Increased strength makes age-hardened materials suitable for high-stress applications.
- Fatigue Resistance: Springs and wire forms become more durable and resistant to metal fatigue.
Materials commonly treated with age hardening (or precipitation hardening) are those that contain specific alloying elements that can form precipitates during the aging process, which strengthens the material. Here’s a full list of materials that respond well to age hardening:
Common Age-Hardened Materials
- Stainless Steels
- 17-4 PH (Precipitation Hardening)
- 15-5 PH
- 13-8 Mo
- PH 13-8 Mo
- Custom 450, Custom 465
- Nickel-Based Alloys
- Inconel 718
- Inconel X-750
- Nimonic alloys
- Rene alloys (e.g., Rene 41, Rene 80)
- Monel K-500
- Hastelloy X
- Aluminum Alloys
- 2000 series (e.g., 2024)
- 6000 series (e.g., 6061, 6063)
- 7000 series (e.g., 7075, 7050)
- Titanium Alloys
- Ti-6Al-4V (Grade 5)
- Ti-10V-2Fe-3Al
- Ti-5Al-2.5Sn
- Cobalt-Based Alloys
- MP35N (Nickel-cobalt-chromium-molybdenum alloy)
- Haynes 25 (L605)
- Copper-Based Alloys
- Beryllium Copper (C17200, C17500)
- Cu-Ni-Sn (Copper-nickel-tin alloys)
- Tool Steels
- Maraging steels (e.g., 18Ni 250, 300 series)
- Aermet steels (e.g., Aermet 100)
These alloys are age-hardened to improve mechanical properties like hardness, tensile strength, and fatigue resistance, making them ideal for demanding applications such as aerospace, medical, marine, and automotive industries.
Spring and Wire Form Applications
Age-hardened materials are ideal for applications where strength, durability, and resistance to wear are critical. Common applications include:
- Compression Springs: Age-hardened compression springs are widely used in aerospace and automotive components where high strength and fatigue resistance are essential.
- Torsion Springs: Age-hardened torsion springs offer superior performance in industrial equipment that endures high stress and repeated loading.
- Medical Springs: Medical springs often undergo age hardening to ensure high durability and resistance to metal fatigue, especially in applications such as implants and surgical tools.
Industries that commonly use age-hardened springs include:
- Aerospace: Age-hardened springs provide the strength and durability needed for flight systems, where performance and reliability are crucial.
- Automotive: Automotive components that undergo high stress, such as suspension systems, benefit from the increased strength and fatigue resistance of age-hardened springs.
- Medical: Age-hardened springs are used in medical implants and instruments where durability, biocompatibility, and resistance to wear are essential.
Learn more about spring applications across industries in From Automotive to Aerospace: Applications of Springs in Different Industries.
Advantages and Limitations of Age Hardening
Advantages:
- Enhanced Strength and Hardness: Age hardening significantly improves the hardness and strength of metal components, making them ideal for high-stress applications.
- Improved Fatigue Life: By creating a more durable structure, age hardening reduces the risk of metal fatigue in springs and wire forms that experience cyclic loading.
- Resistance to Deformation: Age-hardened metals maintain their shape under stress, making them suitable for precision applications where deformation must be minimized.
Limitations:
- Temperature Sensitivity: Some age-hardened materials can lose their strength at very high temperatures, limiting their use in extreme heat environments.
- Complexity and Cost: The age hardening process requires precise control over temperature and timing, making it more complex and potentially more expensive than other treatments.
Age Hardening Compared with Other Treatments
While age hardening primarily improves strength and hardness, other treatments such as surface hardening or shot peening enhance specific surface properties or fatigue resistance. For example, surface hardening focuses on increasing the hardness of the metal’s outer layer, while shot peening improves fatigue life by inducing compressive stress at the surface.
For applications requiring both a hard surface and a tough core, age hardening can be combined with surface treatments to achieve the desired balance of properties for demanding environments.
Future Trends and Innovations
As high-performance industries such as aerospace and medical continue to demand stronger and more durable materials, age hardening remains essential for springs and wire forms. Innovations in multi-stage aging and alloy development are expanding the potential of precipitation hardening, allowing manufacturers to produce springs that are even stronger and more resistant to deformation.
Additionally, automated heat treatment systems are improving the precision and consistency of the age hardening process, making it more accessible for a wide range of applications.
Discover how technology is advancing spring manufacturing in How Automation is Affecting the Future of Spring Manufacturing.
