Bronze is a metal alloy consisting of copper, with its density varying based on the specific alloying elements. Generally, the density of bronze ranges from approximately 7.4 to 9.3 grams per cubic centimeter (g/cm³), or about 0.267 to 0.336 pounds per cubic inch (lbm/in³).
Density of Bronze Alloys
The following table presents the nominal densities for several Unified Numbering System (UNS) designated bronze alloys, which are commonly specified in engineering applications.
| Grades | Description | Alloying Elements | Density (g/cm³) | Density (lbm/in³) |
| C51000 | Phosphor Bronze | Cu, Sn, P | 8.86 | 0.320 |
| C63000 | Nickel-Aluminum Bronze | Cu, Al, Ni, Fe | 7.58 | 0.274 |
| C65500 | High-Silicon Bronze A | Cu, Si, Mn | 8.53 | 0.308 |
| C86300 | Manganese Bronze | Cu, Zn, Mn, Al, Fe | 7.60 | 0.275 |
| C90700 | Tin Bronze | Cu, Sn | 8.78 | 0.317 |
| C93200 | Leaded Tin Bronze | Cu, Sn, Pb, Zn | 8.91 | 0.322 |
| C95400 | Aluminum Bronze | Cu, Al, Fe, Ni | 7.50 | 0.271 |
How to Calculate the Density of Bronze?
Bronze is one of the earliest metal alloys developed by humans. It is an alloy of copper, usually with tin as the main additive. However, bronze alloys can include other elements, such as phosphorus, manganese, aluminum, or zinc, to enhance specific properties such as strength, hardness, or corrosion resistance. The addition of these different elements is the reason for the variation in bronze’s density. Think of it like a smoothie; adding heavy ingredients like protein powder will make it denser than just adding light fruits. Similarly, adding heavier elements like lead to the copper base results in a denser bronze, while lighter elements like aluminum or silicon will lower its density.
As we know, the general formula for density is: ρ=m/V. where ρ is density, m is mass, and V is volume.
For a multi-component alloy like bronze, the bulk density can be approximated by the rule of mixtures, assuming a perfect solid solution without significant volume change upon mixing:
where wi is the mass fraction and ρi is the density of the i-th constituent element. While this provides a theoretical baseline, the actual measured density is influenced by the resulting microstructure, including phase distributions and the potential for porosity.
The primary determinants of a bronze alloy’s density are the atomic masses and atomic radii of its constituent elements. Copper, the base metal, has a density of 8.96 g/cm³.
Addition of heavier elements. Elements with a higher atomic mass than copper, such as tin (Sn,ρ≈7.31 g/cm³) and particularly lead (Pb,ρ=11.34 g/cm³), will modulate the final density. While tin is less dense than copper, its combination in the lattice and the typical inclusion of other elements often result in a dense alloy. Lead, being significantly denser, markedly increases the alloy’s specific gravity.
Addition of lighter elements. Elements with a lower atomic mass, most notably aluminum (Al, ρ=2.70 g/cm³) and silicon (Si, ρ=2.33 g/cm³), will substantially decrease the density of the resulting bronze alloy.
Conclusion
The density of bronze is a variable property, directly correlated with the type and percentage of its alloying elements and influenced by the manufacturing method. It ranges from approximately 7.5 g/cm³ for aluminum-rich alloys to over 8.9 g/cm³ for high-leaded tin bronzes. For engineers, density is not merely a physical constant but a key design parameter that impacts mass properties and structural requirements. A thorough understanding of this property is indispensable for high-quality bronze CNC machining.
