Bronze vs. Brass – What's the Difference?
Long before the days of aluminum and steel, metal alloys were invented, materials created by integrating two synergistic metals together. By doing so, the resulting alloy not only retains some of the properties of each element, but can have new properties not seen in either, which has revolutionized our modern material choices. The two alloys that began this transformation were bronze and brass, ancient metal alloys that have been cast in my country for more than four or five thousand years. These metals provided the starting point for all other alloys, and this article will explore bronze and brass and the differences between them. The physical, chemical, and mechanical properties of bronze and brass will be detailed, as well as the ways in which they are still used today. This article aims to show that these metals, while older than most other engineering materials, are still essential components to our success in the modern era.
Bronze
Bronze is the result of adding tin to copper, although there are usually many additional secondary elements, as bronze was discovered by the Chinese around thousands of years BC, before precise chemistry had been developed. In modern times, bronze is considered a class of copper alloys, defined by their working properties and specific alloying elements. Metals such as lead, manganese, antimony, nickel, zinc, silicon, etc. have been found to improve the properties of bronze, so designers now have a variety of bronze grades to choose from.
Bronze is typically reddish brown/golden in color and is brittle, but lighter than cast iron. It has a relative density of about 8.8 g/cm3 and exhibits low friction when in contact with other metals. It readily conducts heat and electricity, with a melting point ranging from 950 - 1050 °C, depending on the tin content. Due to its high copper content, it oxidizes in air, which gives bronze its distinctive mottled patina. This oxidation prevents bronze from corroding, especially in saltwater environments; however, if chlorine compounds can react with the bronze, a process known as "bronze disease" begins, and corrosion breeds more corrosion, slowly destroying the alloy over time. Its resistance to saltwater makes bronze useful for boat fittings and underwater marine parts, as well as sculptures that must be protected from degradation in the outside environment. It has excellent casting properties and can be easily cast into bearings, clips, electrical connections, springs, etc.
Brass
Brass was discovered around 500 BC and is an alloy of copper and zinc, although it also contains other elements, just like bronze. Because there is a lot of overlap between brass and bronze, brass is often denoted by its high proportion of zinc and relative lack of tin (though confusingly. Tin-plated brass alloys also exist, blurring the lines further). Lead is a common additive to brass to improve its workability, along with other unique elements that make up the brass alloy category.
Brass is bright gold, copper, or even silver, depending on the ratio of zinc to copper. It is more ductile than bronze and exhibits similarly low friction when in contact with other metals. It has a density of about 8.73 g/cm3 and a melting point as low as 900-1000°C, depending on the alloy. Brass is a conductor of heat and is resistant to corrosion, especially to galvanic corrosion from seawater. It casts well, is fairly durable and attractive, and even has some antimicrobial properties due to its high copper content. The most common uses for brass are in musical instruments, decorative trim, screws, radiators, bullet casings, etc.
