1. What material is brass?
Key Characteristics of Brass:
Chemical Composition Foundation: Copper typically accounts for 55%–95% of the alloy, while zinc makes up the remaining 5%–45%. The ratio of Cu to Zn directly determines brass's properties:
High-copper brass (e.g., 70% Cu + 30% Zn): Excellent ductility, corrosion resistance, and machinability, suitable for forming and welding.
High-zinc brass (e.g., 60% Cu + 40% Zn): Higher strength and hardness but reduced ductility, ideal for castings or components requiring rigidity.
Mechanical Properties: Generally exhibits good tensile strength (200–600 MPa, depending on composition and heat treatment), moderate hardness (50–150 HB), and excellent formability (can be rolled, extruded, forged, or drawn into various shapes).
Corrosion Resistance: Resists corrosion from air, water, and most non-oxidizing acids (e.g., hydrochloric acid in low concentrations) but may tarnish over time (a protective oxide layer forms to prevent further degradation). Additions of tin (naval brass) enhance resistance to seawater corrosion.
Other Advantages: Good electrical and thermal conductivity (inferior to pure copper but superior to most steels), natural antimicrobial properties, and an attractive golden appearance (used in decorative applications).
Classification of Brass:
Binary Brass (Cu-Zn Only): Simple alloy of copper and zinc, e.g., red brass (high Cu content, ~85% Cu) and yellow brass (balanced Cu-Zn, ~65% Cu).
Ternary/Quaternary Brass: Alloyed with additional elements to improve specific properties:
Leaded brass (Cu-Zn-Pb): Enhanced machinability (lead acts as a lubricant during cutting), used for fasteners and valves.
Naval brass (Cu-Zn-Sn): Superior corrosion resistance to seawater, used in marine hardware and shipbuilding.
Aluminum brass (Cu-Zn-Al): High strength and corrosion resistance, suitable for high-temperature or high-pressure applications.
