room temperature tissue
Ordinary brass is a copper-zinc binary alloy, and its zinc content varies widely, so its room temperature structure is also very different. According to the Cu-Zn binary state diagram, there are three types of brass at room temperature: brass with a zinc content of less than 35%, the microstructure at room temperature is composed of a single-phase α solid solution, called α brass; zinc-containing Brass with an amount in the range of 36% to 46%, the microstructure at room temperature is composed of (α+β) two-phase, called (α+β) brass (two-phase brass); the zinc content exceeds 46 %~50% of brass, the microstructure at room temperature is only composed of β phase, which is called β brass.
Pressure processing performance
α single-phase brass (from H96 to H65) has good plasticity and can withstand hot and cold processing, but α single-phase brass is prone to moderate temperature brittleness during hot processing such as forging, and its specific temperature range varies with the content of Zn. The change is generally between 200 and 700 °C. Therefore, the temperature during hot working should be higher than 700°C. The reason for the formation of the medium-temperature brittle zone in single-phase α-brass is mainly due to the existence of two ordered compounds, Cu3Zn and Cu9Zn, in the α-phase region of the Cu-Zn alloy system, and the orderly transformation occurs during heating at medium and low temperature, making the alloy brittle; , There are trace amounts of lead, bismuth harmful impurities and copper in the alloy to form a low melting point eutectic film distributed on the grain boundary, resulting in intergranular cracks during thermal processing. Practice shows that adding a small amount of cerium can effectively eliminate the brittleness at medium temperature.
In the two-phase brass (from H63 to H59), in addition to the α-phase with good plasticity, the β-solid solution based on the electronic compound CuZn also appears in the alloy structure. The β phase has high plasticity at high temperature, while the β′ phase (ordered solid solution) at low temperature is hard and brittle. Therefore, (α+β) brass should be forged in a hot state. Beta brass with a zinc content of more than 46% to 50% cannot be processed by pressure due to its hard and brittle properties.
