An alloy of copper with zinc. 70/30 brass, with about 30% Zn, is single-phase α and highly ductile, while 60/40 brass, with about 40% Zn, contains the β phase and is stronger.
Japanese name: 黄銅
Brass appears in 5 practice questions across 5 topics, including Crystal defects and diffusion, Thermal properties of materials, Heat treatment and metallic materials.
Field: Metals and alloys
Answer: A. The two kinds of atoms diffuse at different rates, and diffusion proceeds by the vacancy mechanism
Zinc diffuses into copper faster than copper diffuses into brass, so more atoms leave the brass side than enter it. Substitutional diffusion proceeds by exchange with vacancies, so vacancies flow opposite to the net flow of atoms; lattice planes are lost on the brass side and the markers shift toward the brass. This historic experiment showed that diffusion proceeds by the vacancy mechanism. With only the interstitial mechanism, the number of lattice sites would not change and the markers would not move. Excess vacancies that coalesce form Kirkendall voids, which degrade the reliability of solder joints and similar structures.
Answer: C. Solute atoms scatter conduction electrons and shorten their mean free path, so the thermal conductivity falls along with the electrical conductivity
Heat in metals is carried mainly by conduction electrons, so the thermal conductivity is nearly proportional to the electrical conductivity, the two being linked by the Wiedemann–Franz law. Zinc atoms in the copper lattice disturb the periodicity of the atomic arrangement and scatter electrons, shortening their mean free path, so the electrical conductivity of brass is only about 30% of that of pure copper. The thermal conductivity likewise falls from about 400 to about 120 W/(m·K). Zinc itself is a metal with a thermal conductivity of about 116 W/(m·K), not a substance that fails to conduct heat. In metals, phonons carry only part of the heat to begin with, so a small change in the lattice properties cannot explain such a large drop.
Zinc diffuses into copper faster than copper diffuses into brass, so more atoms leave the brass side than enter it.
When copper and brass (a Cu-Zn alloy) are bonded and heated…Zinc atoms in the copper lattice disturb the periodicity of the atomic arrangement and scatter electrons, shortening their mean free path, so the electrical conductivity of brass is only about 30% of that of pure copper.
The thermal conductivity of pure copper at room temperature…Brass (Cu-Zn), Al-Mg alloys, and Si and Mn in steel are typical examples of solid-solution strengthening.
Which statement about substitutional solid-solution strengt…Brass is copper with zinc added.
Which correctly pairs a copper alloy with its main alloying…Classic examples are austenitic stainless steels in hot chloride environments and brass in ammonia-containing environments (season cracking).
Which statement about stress corrosion cracking is correct?Vacancy Wiedemann–Franz law Phonon Solid-solution strengthening Dislocation Stress corrosion cracking Stainless steel Columnar grains Recovery Recrystallization