In the vast world of metal materials, many advanced material processing technologies have emerged to meet the increasingly stringent performance requirements of modern industry. Precipitation hardening technology plays a vital role in many fields.
Precipitation hardening definition
Precipitation hardening, also known as aging hardening, is a heat treatment process that significantly improves the strength and hardness of materials by introducing a precipitate phase of solute atoms into metal alloys. Simply put, when a specific alloy undergoes a solid solution treatment, the solute atoms are uniformly dissolved in the matrix lattice to form a supersaturated solid solution. Subsequently, aging treatment is carried out at a suitable temperature, and the solute atoms gradually precipitate from the supersaturated solid solution and aggregate to form fine, dispersed precipitation phase particles. These precipitation phase particles are like tiny "obstacles" that hinder the movement of dislocations, making it more difficult to deform the metal material, thereby improving its strength and hardness.
Advantages and characteristics of precipitation hardening
High strength and high hardness
Precipitation hardening can make metal materials obtain extremely high strength and hardness. Taking aluminum alloy as an example, after precipitation hardening treatment, its strength can be increased several times, which can meet the strict requirements of high strength and lightweight materials in the aerospace field.
Good dimensional stability
During the aging process, the changes in the internal structure of the material are relatively uniform, and it is not easy to generate large internal stress, thus ensuring the good dimensional stability of the material.
Excellent corrosion resistance
After precipitation hardening treatment, the surface structure of some alloys changes, forming a denser oxide film, which improves the corrosion resistance of the material.
Adjustable performance
By adjusting the process parameters such as temperature and time of solution treatment and aging treatment, the size, quantity and distribution of the precipitated phase can be accurately controlled, thereby realizing the precise regulation of material properties and meeting the diverse requirements of material properties in different application scenarios.
Precipitation hardening process
Solution treatment
The alloy is heated to a relatively high temperature so that the solute atoms in the alloy are fully dissolved in the matrix lattice to form a uniform supersaturated solid solution.
Quenching and cooling
After solution treatment, the alloy is quickly placed in water or other cooling media for rapid cooling, so that the supersaturated solid solution formed at high temperature can be retained to room temperature, inhibiting the precipitation of solute atoms, thereby obtaining a metastable structure with a high degree of supersaturation.
Aging treatment
The quenched alloy is heated to a relatively low temperature (generally 150 - 250 ° C) and maintained for a certain period of time. At this temperature, the solute atoms in the supersaturated solid solution begin to gradually diffuse and aggregate to form precipitate phase particles. The aging time varies from several hours to tens of hours depending on the type of alloy and the required properties.
Precipitation hardening type segmentation
Precipitation hardening of aluminum alloys
Aluminum alloys are one of the alloy systems with the most extensive application of precipitation hardening technology. According to the different alloy composition and performance requirements, it can be divided into different series, such as 6000 series (main alloying elements are magnesium and silicon) has good strength and corrosion resistance after precipitation hardening, and is often used in building doors and windows, automotive parts, etc.; 7000 series (main alloying elements are zinc, magnesium, and copper) has extremely high strength after precipitation hardening, and is a key material for manufacturing aircraft structural parts in the aerospace field.
Precipitation hardening of copper alloys
Some copper alloys such as beryllium bronze and chromium bronze can also be improved by precipitation hardening.
After precipitation hardening, beryllium bronze has high hardness, high strength, good electrical and thermal conductivity, and excellent elasticity, and is often used to manufacture precision parts such as electronic connectors and springs;
After precipitation hardening, chromium bronze has significantly improved strength and wear resistance while maintaining good electrical conductivity, and is suitable for manufacturing resistance welding electrodes, etc.
Precipitation hardening of stainless steel
Martensitic precipitation hardening stainless steel and austenitic precipitation hardening stainless steel are common types.
Martensitic precipitation hardening stainless steels such as 17-4PH, through precipitation hardening treatment, have high strength and good corrosion resistance, and can also be heat-treated and strengthened, and are widely used in machinery manufacturing, petrochemical and other fields;
Austenitic precipitation hardening stainless steels such as 17-7PH, have excellent formability and corrosion resistance, and their strength is greatly improved after precipitation hardening. They are often used to manufacture aircraft engine parts, pressure vessels, etc.
Precipitation hardening of nickel-based high-temperature alloys
Nickel-based high-temperature alloys have excellent strength and oxidation resistance in high temperature environments. Through precipitation hardening treatment, their endurance strength and creep properties at high temperatures can be further improved.
Precipitation hardening application areas
Aerospace
In aircraft manufacturing, precipitation hardened aluminum alloys, nickel-based high-temperature alloys, etc. are widely used in the manufacture of key components such as wings, fuselages, engine blades, and landing gears.
Precipitation hardened aluminum alloys and high-strength steels are often used in automobile body structural parts, engine parts, and suspension systems. For example, after precipitation hardening treatment, the aluminum alloy wheels of automobiles improve the strength and fatigue resistance of the wheels while ensuring lightweight, and improve the handling and safety of the car; the pistons, connecting rods and other parts of the engine are made of precipitation hardened high-strength steel, which can withstand high temperature, high pressure and high speed working conditions.
In the manufacture of electronic equipment, precipitation hardened copper alloys and stainless steel are used to manufacture electronic connectors, radiators, shielding covers and other parts. The high conductivity, high strength and good elasticity of precipitation hardened copper alloys ensure the reliable connection of electronic connectors during frequent plugging and unplugging.
Medical devices
Precipitation hardening stainless steel is widely used in the manufacture of medical devices due to its good biocompatibility, high strength and corrosion resistance, such as orthopedic implants (artificial joints, bone plates, etc.) and dental devices (dental implants, orthodontic brackets, etc.).
Energy field
In energy industries such as petrochemicals and electricity, precipitation hardening stainless steel and nickel-based high-temperature alloys are used to manufacture pipes, valves, pressure vessels and other equipment. These equipment need to operate for a long time in harsh environments such as high temperature, high pressure and strong corrosion.
As a powerful means of improving material properties, precipitation hardening technology plays an irreplaceable role in various fields of modern industry with its unique advantages and wide applicability. With the continuous advancement of science and technology and the continuous improvement of material performance requirements, precipitation hardening technology is also constantly innovating and developing, and new alloy systems and processing processes are constantly emerging.
