Brass is an alloy made of two metals: copper and zinc.
Copper is the main component, while zinc is an added element.
Classification of Brass:
Ordinary Brass: A binary alloy composed only of copper and zinc.
Special Brass: A multi-element alloy formed by adding other elements (such as lead, tin, manganese, nickel, etc.) to a copper-zinc alloy to improve mechanical properties, corrosion resistance, or machinability.
Main Properties and Uses: Brass is widely used in the manufacture of valves, water pipes, radiators, musical instruments, ornaments, and precision parts due to its wear resistance, ease of machining, and corrosion resistance.
How Does the Zinc Content in Brass Affect its Properties?
The zinc content in brass has a significant impact on its properties, specifically affecting its mechanical properties, machinability, and phase structure. The following is a detailed analysis of the effect of zinc content on brass properties:
Mechanical Property Changes
Low Zinc Stage (Zinc Content ≤ 32%): Brass is a single-phase α solid solution. The solid solution strengthening effect of zinc simultaneously increases tensile strength (σb) and elongation (δ). Plasticity reaches its peak when the zinc content reaches 30%-32%.
Medium Zinc Stage (Zinc Content 32%-39%): A β’ phase (ordered solid solution) appears, forming an α+β’ dual-phase structure. Strength continues to increase, but plasticity decreases because the β’ phase hinders dislocation movement.
High Zinc Stage (Zinc Content > 45%): A hard and brittle γ phase (Cu₅Zn₈ compound) appears, leading to a sharp decrease in both strength and plasticity. Industrially, the zinc content is usually limited to below 47% to avoid the excessive formation of the γ phase.
Processing Properties and Phase Structure
Zinc Content ≤ 35%: The single-phase α solid solution has good ductility and is suitable for cold working (such as wire drawing and rolling). Zinc content 36%-45%: α+β two-phase structure; the β phase has higher hardness, suitable for hot working (e.g., forging, die casting).
Zinc content >45%: Excessive β phase ratio or presence of the γ phase results in a hard and brittle material with extremely poor ductility at room temperature, failing to meet industrial application requirements.
Other performance impacts: Physical properties: With increasing zinc content, brass density, electrical conductivity, and thermal conductivity decrease, while the coefficient of linear expansion increases.
Corrosion resistance: Increased zinc content may reduce corrosion resistance, especially in ammonia- or acidic media, where stress corrosion cracking is more likely.
Industrial application limitations: The zinc content of industrial brass generally does not exceed 47% to balance strength, ductility, and processing properties. Brass with 30% zinc (e.g., H70) exhibits optimal ductility, while brass with 45% zinc (e.g., H55) reaches peak strength but has poorer ductility.
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