Copper and its alloys are widely utilized across various sectors—including electrical, electronics, mechanical manufacturing, and architectural decoration—due to their excellent electrical and thermal conductivity, corrosion resistance, and superior workability. As essential non-ferrous materials, the application of copper and its alloys has continuously expanded from ancient bronze artifacts to modern high-tech electronic devices. Understanding their classification and mastering heat treatment processes is vital for maximizing material performance and meeting the requirements of diverse industrial fields. This article will discuss the types of these common CNC machining materials, including categorizations by composition and application, and provide an exploration of heat treatment processes such as annealing, quenching, and aging.
Classification of Copper and Copper Alloys
According to chemical composition, copper alloys are categorized into the following types:
Copper
It is known as red copper, it typically has a copper content exceeding 99.5%. While it offers exceptional electrical conductivity, thermal conductivity, and corrosion resistance, its strength and hardness are relatively low. Pure copper is commonly used for manufacturing electrical wires, cables, radiators, and other components requiring high conductivity and thermal dissipation.
Brass
An alloy of copper and zinc. Depending on the zinc content, brass is divided into ordinary brass and special brass. Ordinary brass generally contains less than 40% zinc and possesses good processing and mechanical properties, making it suitable for manufacturing pipes, bars, and plates. Special brass incorporates additional alloying elements such as aluminum, manganese, or tin to further enhance specific properties; for instance, aluminum brass offers high strength and corrosion resistance, often used for marine components and valves.
Bronze
It refers to copper-tin alloys, it now serves as a general term for copper alloys excluding brass and cupronickel. Common types include tin bronze, aluminum bronze, and beryllium bronze. Tin bronze features excellent wear resistance, corrosion resistance, and casting properties, commonly used for bearings, gears, and springs. Aluminum bronze provides high strength and heat resistance for parts operating at high temperatures. Beryllium bronze offers extreme strength, elasticity, and conductivity, frequently used for elastic elements and electrical connectors.
Bronze CNC machining can be quite straightforward, provided the correct tools and techniques are employed. Its machinability depends largely on the specific alloy type; for example, phosphor bronze is a preferred material for precision component manufacturing due to its fine grain structure and ease of processing.
Cupronickel
An alloy of copper and nickel, sometimes containing small amounts of zinc or manganese. Cupronickel is valued for its superior corrosion resistance and aesthetic appearance, often used in medical devices, instrumentation parts, and decorative items.
According to industrial applications, they are categorized into the following types:
Heat Treatment of Copper and Copper Alloys
Recrystallization Annealing
This process is mainly used to eliminate cold work hardening generated during processing and to restore ductility. The work-hardened material is heated above its recrystallization temperature (typically 260–280°C for pure copper and 260–350°C for brass), held for a set duration, and then cooled slowly. During recrystallization, deformed grains transform back into distortion-free equiaxed grains, resulting in decreased hardness and strength but improved plasticity and toughness. For example, cold-rolled copper strips can regain the plasticity necessary for subsequent processing through this treatment.
Stress Relief Annealing
Used to eliminate internal stresses generated during casting, welding, or machining. The heating temperature is generally lower than the recrystallization temperature (150–200°C for pure copper and 200–250°C for brass), followed by cooling after a holding period. This prevents deformation or cracking caused by the release of internal stresses during service.
Solution Quenching
Applied to certain copper alloys containing soluble alloying elements, such as beryllium bronze. The alloy is heated to a solution temperature (typically 780–830°C) to fully dissolve alloying elements into the copper matrix, forming a solid solution, followed by rapid cooling (usually water quenching) to obtain a supersaturated solid solution. Quenching significantly increases strength and hardness, though plasticity and toughness may decrease.
Natural Aging
After solution quenching, alloys like beryllium bronze are left at room temperature. The supersaturated solid solution decomposes over time, precipitating fine secondary phase particles that enhance strength and hardness while maintaining some plasticity and toughness. Natural aging is a slow process that requires a long time to reach stable properties.
Artificial Aging
To accelerate the aging process and improve production efficiency, artificial aging is typically employed. The quenched alloy is heated to a specific temperature (generally 300–350°C) and cooled after a holding period. This achieves the desired properties in a shorter timeframe; by controlling the temperature and duration, one can precisely regulate the material's strength, hardness, and plasticity.
Thermomechanical Treatment
This is a composite process that combines plastic deformation with heat treatment. For instance, an alloy may undergo cold deformation followed by aging treatment. Cold deformation introduces a high density of defects and stored energy, which promotes the precipitation and growth of secondary phase particles during aging, thereby increasing strength and hardness more effectively. This treatment maximizes the material's potential to achieve superior integrated properties.
Impact of Heat Treatment on Properties
Annealing allows the grains of copper alloys to regrow, eliminating deformed structures from work hardening and forming uniform equiaxed grains. Quenching enables the alloy to obtain a supersaturated solid solution or a single-phase structure. Aging then causes the decomposition of this supersaturated solution, precipitating fine secondary phase particles that are uniformly distributed throughout the matrix, which significantly influences the alloy's performance.
Annealing improves plasticity and toughness while reducing hardness and strength. Conversely, quenching and aging significantly boost strength and hardness, though ductility may fluctuate. Appropriate heat treatment optimizes the performance of copper alloys to meet industrial demands. For example, beryllium bronze treated with quenching and artificial aging can achieve strength and hardness several times higher than its annealed state while remaining resilient, making it widely used for high-strength, high-elasticity components.
In summary, copper alloys are classified by composition (copper, brass, bronze, cupronickel) and application (electrical, structural, corrosion-resistant, artisanal). Heat treatment—including annealing, quenching, aging, and thermomechanical treatment—is a critical means of improving microstructure and performance. By optimizing these processes, the inherent advantages of copper alloys can be fully realized to meet the evolving demands of modern industry. As technology advances, the requirements for material performance will continue to rise, making the further study of copper alloy classification and heat treatment highly significant.
