Bronze: Definition, Composition, Properties, and Applications

Bronze is a durable alloy that consists of copper and tin. It is known for its distinctive reddish-brown hue. The metal is quite hard and corrosion-resistant. It has high tensile strength, good malleability, and can readily be cast into intricate shapes. Because of this, bronze finds wide-ranging uses in sculptures, coins, bells, bearings, and various industrial applications. 

This article delves into the definition, composition, properties, and applications of bronze. 

What Is Bronze?

Bronze is an alloy that typically has a composition of about 88% copper and 12% tin. However, it’s not uncommon for other elements like aluminum, manganese, silicon, arsenic, phosphorus, silicone, or zinc to be added. These elements yield different properties. Bronze belongs to a family of metals that are known as ‘red metals’ due to their reddish-brown hue. The tin in its crystal structure makes bronze harder than regular copper. It’s also ductile, resists corrosion, and experiences low metal-to-metal friction. 

What Is the History of Bronze?

Bronze has a remarkable history that spans well over six millennia. Archaeologists have found artifacts crafted around 4500 BCE. However, the use of bronze only became common in the 2nd millennium BCE and onward. The Bronze Age dawned in regions like Greece and China before 3000 BCE, while Britain didn’t embrace it until 1900 BCE. Bronze's exceptional hardness and durability revolutionized toolmaking, weapon crafting, and agriculture. Bronze Age civilizations, including Sumer, Babylonia, and Ancient Greece, thrived through trade and cultural exchanges. The Shang and Zhou Dynasties in China, running from 1600-256 BCE, saw bronze used for chariots, weapons, and vessels. However, by around 1300 BCE, iron became accessible. The Iron Age, which ran from roughly 1200-550 BCE, was fueled by that metal’s superior properties. Iron was easier to come by and also easier to process into a usable metal grade. This marked the decline of the Bronze Age. 

Despite its diminished role in tools and weapons, bronze was still valued for statues and ornaments. It has also been used in modern times for 3rd-place sports medals. The tradition originated during the 1904 Summer Olympics in St. Louis, Missouri. Before this, silver medals were awarded to winners, while bronze medals were given to the runners-up. Today, bronze still has a wide variety of applications and can be found in items like springs, bushings, car gearboxes, hammers, ship propellers, musical instruments, and more. 

What Is the Other Term for Bronze?

There is no other term for bronze specifically. However, it does fall under the category of “copper alloy” or “copper-based alloy.” Bronze itself is a specific type of copper alloy, consisting primarily of copper and tin, but the broader term covers combinations of copper with other metals like aluminum, manganese, zinc, or phosphorus. Another example of a copper alloy is brass, consisting primarily of copper and zinc. 

Is Bronze Metal the Same as Copper?

No, bronze is not the same as copper. Bronze is an alloy that contains copper as part of its composition. 

To learn more, see our article on the Characteristics of Copper.

What Is Bronze Made Of?

Bronze is made of copper and tin. Tin usually makes up around 12% of the total, with the remaining 88% being copper. The specific proportions vary based on use and manufacturer. It’s also possible for other elements to be included in the alloy mix. These elements include, but are not limited to: arsenic, aluminum, manganese, silicon, and phosphorus, which are added to alter certain properties. Different elements give the metal different levels of ductility, hardness, flexibility, and other properties. Some common bronze alloys include: aluminum bronze, leaded bronze, phosphorus bronze, silicon bronze, and manganese bronze.  

How Are Bronzes Made?

Bronze is typically made through a process called bronze casting, which involves melting and combining copper and tin in specific proportions. Once these two metals are melted, the mix is poured into a mold where it is left to cool and solidify into objects such as sculptures, medals, instruments, tools, and more. Bronze casting methods include lost wax casting, sand casting, and ceramic shell casting. 

What Are the Characteristics of Bronze?

Some of the common characteristics of bronze include:

1. Reddish-brown metallic color
2. Hard 
3. High ductility, but it becomes brittle under extreme forces
4. Good surface finish 
5. Excellent thermal and electrical conductivity 
6. Good corrosion resistance 
7. Good fatigue resistance
8. Low metal-to-metal friction 
9. High Melting point (950°C)
10. Non-sparking and non-magnetic properties 

What Is the Color of Bronze?

Bronze has a metallic brown color with a reddish hue. That is why it falls under the category of “red metals.” 

What Does Bronze Look Like?

The appearance of bronze can vary depending on factors such as its composition, age, and exposure to environmental conditions. Freshly cast bronze has a metallic brown color.

Over time, as the bronze oxidizes, it develops a patina that alters its appearance. The patina typically starts as a shiny golden brown, then transitions to various shades of brown. Eventually, it may develop into a greenish tint. The greenish hue (see Figure 1) is often associated with copper carbonate, a compound formed through the oxidation process:

This patina is a natural and protective layer that forms on the surface of the bronze, providing some resistance against further corrosion.

What Are the Different Types of Bronze?

There are a lot of different bronze alloy types. Some of these include:

1. Aluminum bronze (6-12% aluminum).
2. Nickel aluminum bronze (6-13% aluminum; up to 7% iron; 7% nickel).
3. Silicon bronze (up to 6% silicon).
4. Phosphor bronze, or tin bronze (up to 11% tin and up to 0.35% phosphorus).
5. Manganese bronze (up to 3% manganese).

To learn more, see our article on the Types of Bronze.

What Are the Properties of Bronze?

The chemical and physical properties of bronze are given in the sections below:

What Are the Physical Properties of Bronze?

The physical properties of bronze are outlined in Table 1: 

What Are the Chemical Properties of Bronze?

The chemical properties of bronze are given in Table 2:

What Are the Applications of Bronze?

Bronze is very versatile and has many applications, such as those below:

1. Tools

Toolmaking and weapon crafting were among the earliest uses of bronze. At the time it was one of the hardest and most corrosion-resistant metals, so bronze was ideal for tools and weapons that can be prone to wear and tear. Tools that are still commonly made from bronze include things like: wrenches, hammers, chisels, and blades, among others. It is also commonly used for bearings, gears, worm wheels, bushings, and more. 

2. Architecture

Bronze is a staple in the architecture industry. Here it is commonly used for decorative elements, structural components, or artistic features. Some examples of architectural use of bronze include door or window frames, cabinet hardware (e.g. handles), furniture hardware, trim, etc. Architectural bronze typically preserves the natural color and finish of raw bronze, whereas outdoor sculptures or ornaments typically go for the patination of bronze. 

3. Coins

Bronze and copper were two of the main coinage metals during ancient times. Bronze coins were traditionally made from copper, tin, and zinc alloy. Modern coins, however, have replaced it with copper-plated steel, zinc, or nickel because of changes in the metals’ relative prices. The new coins are the same weight, color, and design as the bronze ones with no notable differences other than their magnetic properties. 

4. Instruments

Bronze is commonly used to make different kinds of instruments like cymbals, bells, and gongs. They’re cast in a particular formulation called “bell metal.” Other bronzes like phosphor bronze can also be used to produce acoustic guitar and piano strings, though that one makes for good bells as well. 

5. Bells

Bronze is used for bells due to its durability and ability to produce a clear and strong tone. Bronze bells are constructed of “bell metal” which consists of 80% copper and 20% tin — a composition that generates appealing sounds and resonance. The 4:1 ratio of copper to tin in this bronze creates a specific crystal lattice arrangement, enhancing the alloy's ability to absorb energy (damping capacity) and optimize sound velocity. This unique combination is responsible for the resonant toll of bells and idiophones like cymbals, allowing the sound to travel across neighborhoods.

6. Bearings

Bronze can be used to make lots of things like springs, bearings, and bushings, especially for car transmissions and small electric motors. Bearing bronze is a specific formulation that’s perfect for bushings and bearings due to its strength and hardness. These bearings resist shock, impact, wear, and corrosion. Such bushings and bearings do, however, require an external lubricant like oil or grease to reduce friction or wear. Bronze bushings and bearings find frequent application in industrial settings characterized by low speeds, high loads, and demanding conditions. They are commonly employed in machinery used for iron and steel manufacturing, food processing, injection molding, automotive equipment, earthmoving machinery, pumps, and various other industrial tasks. 

7. Medals

Medals are another common use of bronze. Bronze medals are typically associated with 3rd place in sports competitions and related events. The tradition started in the 1904 Summer Olympics in St. Louis, Missouri. Before this, silver medals were given to first-place winners, while bronze medals were given to the runners-up.

8. Bronze Casting

Bronze casting is a traditional metalworking process with a rich history that spans civilizations. Molten bronze is poured into a carefully crafted mold to create objects and sculptures. Bronze casting has historically served to manufacture tools, weapons, sculptures, bells, and much more. 

What Are the Advantages of Bronze?

Bronze has the following advantages:

1. It is much harder than pure copper or iron.
2. It has better corrosion resistance, heat and electrical conductivity, and resistance to fatigue compared to most steels. 
3. Because it’s more fusible than copper, it is easier to cast. 
4. The friction coefficient is lower than that of copper.
5. It is versatile and durable and can be used for a wide range of applications.

What Are the Disadvantages of Bronze?

Some of the disadvantages of bronze include:

1. It’s typically more costly than steel, brass, and copper.
2. Bronze tends to oxidize more easily than copper. 
3. Due to its hardness, bronze can be more difficult to work with compared to pure copper.
4. It has limited resistance to ferric compounds, ammonia, and cyanides. Sulfur and chlorine in a humid environment can cause bronze to deteriorate. 
5. A condition known as Bronze Disease, evident through small, pale green rough spots that appear suddenly may occur when oxygen and chloride react in water. The result is hydrochloric acid which causes corrosion similar to rust in iron-based metals. If unchecked, this process forms copper and tin chlorides and will destroy the bronze.

Does Bronze Get Rust?

No, bronze does not rust because it contains no iron. Therefore, iron oxide, known as rust, cannot form on its surface. However, despite its corrosion resistance, bronze is susceptible to oxidation. When bronze oxidizes, it develops a distinctive lime-green or blue-green patina. However, proper treatments will preserve its original metallic brown properties. The oxidation process results in the formation of a single layer of copper oxide that eventually transforms into copper carbonate. This oxidation occurs only on the external layer, forming a protective barrier that shields the interior metal from further oxidation. 

Does Bronze Turn Green?

Yes. While bronze does not rust, it is still prone to oxidation. This produces a lime green or blue-green colored patina on the surface. However, the bronze can be treated to preserve its metallic brown appearance. 

Is Bronze an Alloy?

Yes, bronze is an alloy that traditionally consists of tin and copper. 

Is Bronze a Strong Metal?

Yes, bronze is considered to be a strong ductile metal. 

What Is the Difference Between Bronze and Brass?

The difference between brass and bronze lies in their composition and properties, despite both being copper alloys. Brass, an alloy of copper and zinc, boasts a bright gold, copper, or silver color, depending on the added metals. It is more malleable than bronze, making it less prone to breaking when hammered or rolled. Bronze, on the other hand, is an alloy of copper and tin, exhibiting a reddish-brown hue that turns dark brown or green when oxidized. Though less malleable than brass, bronze is renowned for its acoustic properties, producing a duller and deeper sound, ideal for instruments like cymbals and bells. Additionally, both alloys are corrosion-resistant, but bronze develops a protective patina, while brass tarnishes over time.

Summary

This article presented bronze, explained it, and discussed its properties and various applications. To learn more about bronze, contact a Xometry representative.

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