Copper and its alloys are among the earliest metal materials used in human history. Their excellent electrical and thermal conductivity, ductility, and corrosion resistance have secured them an irreplaceable position in the electronics, electrical engineering, machinery, aerospace, and other fields. Pure copper, also known as red copper, is purple-red in color and typically has a purity exceeding 99.5% . It possesses extremely high electrical conductivity ( 58.5 MS/m at 20 °C ) and thermal conductivity ( 398 W/(m・K) ), but relatively low strength (tensile strength approximately 220 MPa ), making it easy to form. To improve the mechanical and functional properties of pure copper, copper alloys are formed by adding alloying elements (such as zinc, tin, aluminum, nickel, and lead). Depending on the alloying elements, copper alloys can be divided into three categories: brass, bronze, and white copper. Each alloy type has multiple grades to suit different usage environments and processing requirements.
Brass is a copper alloy with zinc as the primary alloying element. It can be divided into common brass and special brass depending on the zinc content. Common brass has a zinc content between 30% and 45%. For example, H62 (62% copper, 38% zinc) exhibits excellent plasticity and strength, making it suitable for cold working such as stamping and bending. H80 (80% copper, 20% zinc) exhibits excellent plasticity and is often used in bellows, condenser tubes, and other applications. Special brass is made by adding other elements (such as lead, tin, aluminum, and manganese) to common brass to improve specific properties. For example, HPb59-1 (1% lead) offers excellent machinability and is suitable for threaded parts such as nuts and bolts. HSn62-1 (1% tin) exhibits excellent seawater corrosion resistance and is commonly used in marine components. The color of brass changes from golden yellow to pale yellow as the zinc content increases. Its conductivity is about two-thirds that of pure copper, but its strength is significantly higher (H62 has a tensile strength of 330 MPa). Its cost is lower than pure copper, making it the most widely used copper alloy.
Bronze is a general term for all copper alloys except brass and cupronickel. Originally, tin bronze was primarily alloyed with tin, but later evolved into various types, including aluminum bronze, lead bronze, and beryllium bronze. Tin bronze (such as QSn4-3, containing 4% tin and 3% zinc) offers excellent wear resistance and casting properties, making it suitable for wear-resistant parts such as bearings and gears. Aluminum bronze (such as QAl9-4, containing 9% aluminum and 4% iron) offers high strength (tensile strength up to 600 MPa) and excellent corrosion resistance, making it a suitable replacement for some steel in structural parts. Beryllium bronze (such as QBe2, containing 2% beryllium) is an age-hardened alloy. After solution treatment and aging, it can reach a hardness of 35-40 HRC. It has excellent elasticity and conductivity and is commonly used in precision springs, electrical contacts, and other applications. Bronze is mostly bluish-gray in color, and its properties vary significantly. Tin bronze offers good plasticity, aluminum bronze offers high strength, and beryllium bronze combines high strength and high elasticity, meeting the functional requirements of various scenarios.
White copper is a copper alloy with nickel as the primary alloying element. It can be divided into standard white copper and complex white copper based on the nickel content. Standard white copper, such as B19 (19% nickel), has excellent corrosion resistance and low-temperature toughness and is commonly used in the manufacture of medical devices and precision instrument parts. B30 (30% nickel) has excellent antimagnetic properties and is suitable for magnetic shielding components. Complex white copper, with added elements such as zinc, manganese, and iron, such as BMn40-1.5 (manganese white copper), has an extremely low temperature coefficient of resistance and is a key material for thermocouples and resistors. BZn15-20 (zinc white copper), similar in appearance to silver and also known as “German silver,” is commonly used in decorative pieces and tableware. White copper has superior corrosion resistance to brass and bronze, especially in environments such as seawater and organic acids. However, its higher cost means it is primarily used in applications requiring high corrosion resistance.
The processing technology for copper and copper alloys must be selected based on the material’s properties. Pure copper and low-zinc brass have excellent plasticity and are suitable for cold working (such as cold rolling, cold drawing, and cold stamping). Cold working will produce work hardening and require annealing (temperature 300-600°C) to restore plasticity. High-zinc brass and bronze have less plasticity and are often hot-worked (such as hot rolling and hot forging) at temperatures of 700-900°C to avoid overheating that can lead to coarse grains. Regarding cutting, lead brass (such as HPb59-1) offers excellent cutting performance and can be cut at high speeds (cutting speeds of 100-300 m/min) with a tool rake angle of 15°-20° to reduce cutting forces. Aluminum bronze, due to its high strength, requires carbide tools (such as YG8) at cutting speeds of 50-100 m/min and feeds of 0.1-0.2 mm/r. When welding pure copper and brass, either gas welding or argon arc welding can be used, while bronze and cupronickel require argon arc welding. Before welding, the surface oxide film must be cleaned to prevent the formation of pores. Surface treatments for copper and copper alloys include electroplating (chrome plating, nickel plating) and oxidation coloring to enhance wear resistance and decorative properties. By properly selecting material grades and processing techniques, the excellent properties of copper and copper alloys can be fully utilized to meet the application needs of various industries.
