As a copper-zinc alloy, the improvement of the overall mechanical properties of brass relies heavily on the precise control of heat treatment processes. By rationally designing the heat treatment process, the strength, toughness, wear resistance, and corrosion resistance of brass can be effectively improved to meet the needs of various industrial applications. The core logic lies in using heating, holding, and cooling steps to alter the internal microstructure of the material, eliminate processing defects, and optimize the distribution of alloying elements, thereby enhancing overall performance.
Low-temperature annealing is one of the fundamental heat treatment processes for brass. Its main purpose is to eliminate internal stress and prevent seasonal cracking. Residual stress is generated in brass during cold working, especially in alloys with high zinc content. Prolonged exposure to humid or ammonia-containing environments can easily lead to stress corrosion cracking. Low-temperature annealing, by heating brass to 260–350°C, holding it at that temperature for 1–3 hours, and then air-cooling it, can effectively release internal stress and improve the dimensional stability of the material. This process is particularly important for the machining of precision parts, such as electronic connectors and instrument components, to ensure that their performance does not degrade due to stress relaxation during long-term use.
Recrystallization annealing is used for work-hardened brass, restoring its plasticity to prepare it for subsequent processing. During cold rolling and drawing processes, brass undergoes grain deformation, leading to increased hardness and decreased toughness. Recrystallization annealing, by heating to 500–700℃, causes the material to recrystallize, forming uniform, fine equiaxed grains, thus restoring its plasticity. For example, H62 brass requires annealing at 600–650℃ after cold drawing before subsequent deep drawing or bending. This process is widely used in pipe and strip production to ensure the material does not crack or wrinkle during complex deformation processes.
Solution treatment is a key method for improving brass strength, especially suitable for special brass containing alloying elements such as lead and aluminum. By heating to a high temperature and holding for a certain time, the alloying elements are fully dissolved in the copper matrix, forming a uniform solid solution. For example, after solution treatment at 700–750℃, C36000 lead brass exhibits a uniform distribution of lead particles at the grain boundaries, significantly improving machinability while maintaining high strength. Solution treatment requires strict control of temperature and time to avoid overheating leading to grain coarsening or insufficient holding time causing elemental segregation.
Aging treatment is often used in conjunction with solution treatment. By holding at a low temperature for a long time, solute atoms precipitate, forming a dispersed strengthening phase. For example, after solution treatment, C54400 brass undergoes aging treatment at 300–400℃, which precipitates fine intermetallic compounds, hindering dislocation movement and thus improving tensile strength and wear resistance. Aging is particularly important for components in the aerospace and automotive industries, such as gears and bushings, which need to maintain long-term stability under high-temperature and high-load environments.
The combined quenching and tempering process is used for the preparation of high-strength brass. Rapid cooling (such as water quenching) fixes the high-temperature structure, followed by low-temperature tempering to eliminate internal stress and adjust the balance between hardness and toughness. For example, high-alumina bronze, quenched at 850–900℃ and then tempered at 300–350℃, yields a structure with both high strength and good toughness, suitable for manufacturing molds and wear-resistant parts. The quenching process requires strict control of the cooling rate to avoid cracking, while the tempering temperature must be precisely selected based on performance requirements.
Cyclic heat treatment is an emerging process that refines grain size and improves overall performance through multiple heating-cooling cycles. For example, multiple cycles of treatment at 500–600℃ can reduce the grain size to one-third of its original size in Brass, significantly improving strength and ductility. This process has potential in high-end manufacturing fields, such as precision instruments and medical devices, where materials require both high strength and high reliability.
The heat treatment process for Brass needs to be customized according to the specific alloy composition and application scenario. Low-temperature annealing to relieve stress, recrystallization annealing to restore plasticity, solution treatment and aging to improve strength, quenching and tempering to adjust toughness, and cyclic heat treatment to refine grain size—each process is interconnected, jointly constructing a complete system for optimizing Brass performance. By precisely controlling heat treatment parameters, Brass can be widely used in electrical, mechanical, automotive, and aerospace fields, becoming an indispensable basic material in modern industry.
