CZ121PB4

CZ121PB4 is a free machining brass alloy and a significantly improved variation of the 60/40 brass alloy, known for its excellent free cutting properties. This alloy is used extensively in mass production where high output and long tool life are critical. It features a fine dispersion of lead throughout the microstructure, acting as a lubricant and chip breaker to provide outstanding machinability.

Chemical Composition

• Copper (Cu): 56.5 – 58.5%

• Lead (Pb): 3.5 – 4.5%

• Iron (Fe): Up to 0.30%

• Total Others (including Sn, Ni, etc.): Up to 0.7%

• Zinc (Zn): Remainder (balance)

Mechanical Properties

• Tensile Strength: Typically 360 – 500 MPa

• Proof Stress: Approximately 220 – 350 MPa

• Elongation: 5% – 20% depending on form and temper

• Hardness: 90 – 160 Brinell Hardness Number

Physical Properties

• Density: 8.47 g/cm³

• Melting Point: Around 875 °C (Solidus)

• Modulus of Elasticity: Around 97 GPa

• Electrical Resistivity: 0.62 x 10⁻⁶ Ω·m

• Thermal Conductivity: About 123 W/m·K

• Coefficient of Thermal Expansion: 20.9 x 10⁻⁶ /K

Fabrication and Application

• Machinability rated at 90% relative to free machining brass alloys

• Excellent for hot forging and suitable for high-speed machining operations

• Commonly used for manufacturing fasteners, extruded sections, precision parts, window frames, valve components, and locking devices

• Fair corrosion resistance with a bright golden appearance