Room temperature structure
Brass, a binary alloy made of copper and zinc, is a versatile material that is used in a wide range of applications. One of the reasons for its versatility is that its zinc content can vary, which results in different room temperature microstructures. Based on the Cu Zn binary state diagram, there are three main types of room temperature microstructure for brass. When the zinc content is less than 35%, the microstructure is comprised of a single-phase α solid solution composition, which is known as α brass. For brass with a zinc content between 36% and 46%, the microstructure consists of a two-phase composition of α and β, and is referred to as (α+β) brass, or two-phase brass. When the zinc content is between 46% and 50%, the microstructure at room temperature only consists of β phase composition, and is referred to as β brass.
Pressure processing performance
α Single phase brass, ranging from H96 to H65, exhibits excellent plasticity and can withstand both cold and hot working processes. However, it is susceptible to medium temperature brittleness during hot working operations like forging. The specific temperature range for this brittleness varies based on the zinc (Zn) content, typically falling between 200 ℃ and 700 ℃. To mitigate this issue, the temperature during hot working must be set higher than 700 ℃.
The medium temperature brittle zone in single-phase α brass primarily occurs due to two ordered compounds, namely Cu3Zn and Cu9Zn, found within the α phase region of the copper-zinc alloy system. These compounds undergo an ordered transformation when exposed to medium and low temperatures, leading to brittleness in the alloy. Additionally, the presence of trace amounts of lead and bismuth impurities in the brass creates a low melting point eutectic film, which forms along the grain boundaries. This phenomenon promotes intergranular fracture during hot working processes.
Practical experience has shown that the addition of trace amounts of cerium can effectively eliminate the medium temperature brittleness in α single phase brass.
Brass is a popular alloy that is commonly used in many industrial applications. Two phase brass, specifically in the H63 to H59 range, is known for its exceptional plasticity and its ability to resist electronic compounds. This includes copper-zinc-based β solid solution, which provides even greater plasticity at high temperatures. However, the ordered solid solution (β′ phase) is quite hard and brittle, leading to difficulties in processing.
When working with brass that consists of both α and β phases, it is best to do so in a hot state. This allows for easier forging and shaping, resulting in a more refined product. As for brass with a zinc content exceeding 46% to 50%, it is impossible to press due to the hard and brittle nature of the β phase. Despite its limitations, brass remains a sought-after alloy for its unique properties and versatility in many industries.
mechanical property
The zinc content plays a crucial role in determining the mechanical properties of brass. α Brass exhibits an interesting trend where an increase in zinc content leads to an increase in both σ B (room temperature strength) and δ (ductility). However, for (α+β) Brass, the strength continues to rise as the zinc content reaches approximately 45%. Beyond this point, an undesirable effect occurs, resulting in a sharp decline in strength. This can be attributed to the formation of a brittle r phase, which is a solid solution based on the Cu5Zn8 compound. As a consequence, the room temperature plasticity of (α+β) Brass consistently decreases with increasing zinc content. Hence, copper zinc alloys with zinc content exceeding 45% prove to be impractical due to their unfavorable mechanical properties. It is important to note that this rearranged content is derived from the original text information, maintaining its basis while presenting a highly similar version.
Brass is a commonly used material in various applications, including the production of water tank belts, water supply and drainage pipes, medals, corrugated pipes, serpentine pipes, condenser pipes, cartridge cases, as well as intricate stamped products and small hardware. When the zinc content increases from H63 to H59, brass exhibits great thermal processing capabilities, thereby finding extensive usage in machinery and electrical appliances, stamping parts, and even musical instruments.
To enhance the corrosion resistance, strength, hardness, and machinability of brass, the addition of trace elements such as tin, aluminum, manganese, iron, silicon, nickel, lead, and others (typically ranging from 1% to 2%, occasionally reaching 3% to 4%, and rarely exceeding 5% to 6%) is employed. These elements are incorporated into the copper zinc alloy, resulting in the formation of ternary, quaternary, or even quinary alloys, which are commonly referred to as complex brass or special brass.
Zinc equivalent coefficient
The determination of complex brass structure relies on the "zinc equivalent coefficient" associated with the added elements. By introducing small amounts of various alloying elements into the copper-zinc alloy α/(α+β), the phase region can be shifted towards the left or right. As a consequence, the structure of special brass can be compared to that of regular brass with either increased or decreased zinc content. To illustrate, the structure achieved by incorporating 1% silicon into the Cu Zn alloy is equivalent to adding 10% zinc into the same alloy. Hence, the "zinc equivalent" of silicon is 10, signifying its significant impact on altering the phase boundary α/(α+β) toward the copper side, resulting in a notable contraction of the α phase area. Conversely, the "zinc equivalent coefficient" of nickel is negative, indicating an expanded α phase region. To summarize, the determination of brass structure involves evaluating the impact of different alloying elements, expressed through their respective "zinc equivalent coefficients," which subsequently influence the distribution of α and β phases.
