Brass is a metal alloy composed primarily of copper and zinc. This alloy has been in use since prehistoric times, prized for its pleasing gold-like appearance and its outstanding workability. Brass is non-ferrous, meaning it does not contain iron, which contributes to its resistance to rust and corrosion. The ability to easily shape and machine brass, along with its durability, has made it a popular material for everything from ancient artifacts to modern industrial components.
The Core Elements and Ratios
Brass is composed of copper ($\text{Cu}$) and zinc ($\text{Zn}$), with copper always being the major component by weight. Copper content typically ranges from 60% to 90%. This composition fundamentally distinguishes brass from bronze, which is a copper alloy primarily containing tin.
The most common commercial grades usually fall within a mix of 60% to 70% copper and 30% to 40% zinc. The exact percentage of zinc determines the specific classification of the alloy, such as the single-phase alpha brasses which have less than 37% zinc. Trace elements are sometimes added to fine-tune the material’s performance. These minor additives can include tin for corrosion resistance, lead to improve machinability, or aluminum for increased strength.
How Composition Affects Material Characteristics
The ratio between copper and zinc directly dictates the final physical and mechanical properties of the brass alloy. Increasing the zinc content beyond the copper-rich alpha phase generally leads to a harder and stronger material overall. Alloys with higher zinc content, such as the two-phase alpha-beta brasses, exhibit increased tensile strength but are often less ductile at room temperature.
Conversely, brasses with a higher proportion of copper, such as those with less than 15% zinc, are significantly softer and more malleable. This higher copper content makes them easier to shape and form through cold-working processes like pressing or drawing. The copper-to-zinc ratio also influences the alloy’s color; higher copper content yields a reddish hue, while increased zinc shifts the color toward paler yellow. Furthermore, the addition of zinc beyond approximately 15% can increase the alloy’s susceptibility to a form of corrosion known as dezincification, where zinc is selectively leached out of the material.
Distinct Varieties and Common Applications
The precise formulation of brass allows engineers to create specific alloys tailored for unique end-uses, often involving minor additives to enhance a particular trait. For example, Cartridge Brass is an alpha brass alloy containing 70% copper and 30% zinc, which is highly prized for its excellent ductility and cold-working properties. This makes it the standard material for manufacturing ammunition casings, as it can be deep-drawn into its final form.
Another specific formulation is Naval Brass, which typically contains about 60% copper and 39% zinc, but includes a small addition of 1% tin. The tin component is incorporated specifically to suppress dezincification, making Naval Brass highly resistant to saltwater and suitable for marine hardware.
Red Brass, which is a high-copper alloy, contains a significantly lower zinc content, often around 5% zinc with the remainder being copper and trace elements. This composition provides superior corrosion resistance, making it a preferred material for plumbing fittings and valves.