Bronze: Properties, Types, Advantages, Disadvantages, Applications

Bronze, an alloy composed primarily of copper and tin, has been widely utilized across different historical periods for a diverse range of applications. Historically, the primary applications of this material have predominantly revolved around the production of sculptures, coins, and tools, owing to its notable characteristics of hardness, durability, and malleability. During the Bronze Age, this particular metal was widely recognized as the most durable among commonly used metals. Its significance has persisted into modern times, where it remains a crucial metal.

The bronzes are a group of copper-based alloys that have historically been combined with tin, although they may also include alloys of copper with various other elements such as aluminum, silicon, and nickel. Bronze alloys exhibit a relatively higher strength compared to brass alloys, albeit retaining an exceptional degree of resistance against corrosion. In many cases, these materials are employed when there is a need for both favorable tensile properties and resistance to corrosion.

Table of Contents

What is a bronze alloy?

Bronze, an alloy (a mixture of two or more metals), is primarily composed of copper and tin. Most modern bronze contains 89% copper and 11% tin, but this ratio might vary depending on the desired characteristics of the metal. This fusion produces a metal that is more durable than each element alone while retaining some ductility. Bronze alloys can be created by adding trace amounts of other metals like lead, zinc, aluminum, nickel, manganese, phosphorus, arsenic, and silicon.

Bronze sculpture [Image source: metmuseum

Properties of Bronze

The spectrum of bronze encompasses a range of colors, from brown to golden.
This alloy is widely recognized for its exceptional ductility.
Generally, it exhibits a lower level of luster compared to brass.
There exist slight variations in the melting points of brass and bronze.
Ring-shaped surface markings are common in both bronze and brass.
Bronze exhibits a high degree of malleability.
The level of friction exhibited between bronze and other metals is minimal.
When bronze is struck against a hard surface, no sparks are produced. This qualifies the alloy for usage with combustible or explosive materials.
Unlike other metals, bronze expands slightly when it cools after being melted. This is perfect for casting since the metal will solidify into the mold without any gaps.
Bronze is more durable than cast iron because it is not as fragile.
The melting point of the alloy is lower than that of iron or steel.
Bronze is a superior heat and electricity conductor compared to most steels.
Bronze undergoes oxidation upon exposure to atmospheric conditions, resulting in the acquisition of a dull copper patina. Nevertheless, the patina solely impacts the superficial layer, providing protection to the underlying metal. The primary constituent of the patina is copper oxide, which undergoes a chemical transformation into copper carbonate as time progresses.
While bronze will rust in salt air, its patina will protect it from corrosion in fresh water. Widespread corrosion, also known as “bronze sickness,” is caused by chlorides. However, unlike copper and brass, bronze often exhibits high resistance to corrosion from salt water.

Composition of Bronze

Bronze is composed of approximately 88% copper, accompanied by approximately 12% tin and additional metallic elements such as aluminum, zinc, nickel, manganese, and lead. In certain cases, bronze may also contain metalloids or nonmetals such as arsenic, silicon, and phosphorus.

Types of bronze

Aluminum Bronze: From 6% to 12% of aluminum bronze is made up of iron, nickel, and aluminum. It is a strong metal that doesn’t wear down or rust easily. Aluminum bronze is the best metal for pumps, valves, and other tools that will be in contact with fluids that will eat away at them.
Cupronickel: Cupronickel refers to a bronze alloy that is composed of copper and nickel, with nickel content ranging from 2% to 30%. The alloy demonstrates notable thermal stability and a high degree of resistance to corrosion, particularly in environments involving steam or moist air. In the context of seawater, it exhibits superior properties compared to alternative forms of bronze. Cupronickel finds various applications in the marine industry, including ship hulls, pumps, valves, electronics, and marine gear.
Silicon Bronze: Both red silicon bronze and red silicon brass are constituents of silicon bronze. Red bronze contains a lower zinc content compared to red brass, the latter of which consists of 20% zinc and 6% silicon. Silicon bronze exhibits a decreased concentration of lead, alongside the potential presence of manganese, tin, or iron. Silicon bronze exhibits exceptional strength and displays a high level of resistance against corrosion. Silicon bronze is commonly utilized for the fabrication of numerous pumps and valve stems owing to its advantageous characteristics.
Nickel silver: Nickel silver, despite its common name, is not silver. It was named for its silvery appearance. The elements zinc, nickel, and copper can all be found in nickel and silver. It is capable of resisting considerable amounts of force and has decent corrosion resistance. Nickel silver is used in several products, including tableware, decorations, optics, and even musical instruments.
Tin Bronze: Phosphor bronze, often known as tin bronze, contains tin concentrations of 0.5-1.0% and phosphorus concentrations of 0.01-0.035%. This alloy is not only hard and sturdy, but also possesses fine grain, a low coefficient of friction, and a high fatigue resistance. Phosphor bronze is used for a wide variety of applications, including bellows, washers, electrical equipment, and springs.
Manganese Bronze: Manganese bronze is an alloy of copper, zinc, aluminum, iron, and up to 3% manganese. It can absorb impact without breaking, instead deforming. Because of its high durability and resistance to corrosion in salt water, it is commonly used for boat propellers. Manganese bronze is also used for gears, nuts, and bolts.
Bismuth Bronze: Bismuth bronze contains between 1 and 6 percent bismuth. It is more malleable, resistant to corrosion, and a good thermal conductor. Because it polishes so well, it is sometimes used in mirrors and light reflectors. Most often, bearings can be found in an industrial setting. However, traditionally, it has been used in the kitchen. It has replaced leaded bronze in several contexts.

Difference between Bronze and Brass

Current definitions distinguish between bronze and brass, both of which are alloys of copper and zinc. Historically, it has been difficult to distinguish between the two alloys. Bronze, the Italian word for “bell metal or brass,” originates from the old Persian word for brass. The French word bronze itself derives from the Italian word bronze, hence the term “bronze” itself comes from the French. Because of their varied compositions, earlier artifacts are properly categorized as “copper alloys.”

Advantages of bronze

One of the most versatile copper alloys is bronze, which has several common uses. Bronze’s malleability and durability have made it a popular material for a wide variety of uses for hundreds of years, including sculpture, coins, and jewelry.

Durability: One of the primary factors influencing individuals’ preference for bronze in comparison to alternative copper alloys is its exceptional durability and extended lifespan. In contrast to pure copper, bronze exhibits enhanced resistance to corrosion owing to its elevated tin composition. This implies that the material possesses the ability to withstand high temperatures and adverse weather conditions without exhibiting signs of deterioration. This characteristic renders it well-suited for various outdoor applications, including sculptures, landscaping accents, and even boats.

Versatility: Bronze exhibits remarkable versatility and finds extensive utility across a wide range of applications. Owing to its inherent malleability, this material exhibits a remarkable capacity to assume various forms and dimensions with ease. Additionally, it possesses exceptional machinability, thereby enabling the facile cutting or molding of intricate forms with minimal exertion. This characteristic renders it an optimal selection for complex undertakings such as jewelry fabrication or coin minting. Furthermore, the inherent color of bronze imparts an aesthetically pleasing appearance that exhibits long-lasting stability, unlike certain other metals that may experience fading effects with the passage of time.

Affordability: Last but not least, bronze’s competitive price makes it stand out among copper alloys. Because of its abundance in nature, bronze is far more reasonably priced than pure copper, making it accessible to people of all socioeconomic backgrounds. This makes it a great option for monumental sculptures and monuments where budget is a concern.

Aesthetic Appeal: For centuries, bronze has served as a prominent material in the development of sculptures, statues, coins, and various other artifacts. The rationale behind this is that Bronze possesses an inherent aesthetic appeal. The object exhibits a visually pleasing appearance characterized by a reddish hue. Bronze, a malleable metal capable of being elongated into a slender form, exhibits the property of being amenable to intricate carving prior to fracturing. This feature facilitates the shaping of the material into the intended forms.

Easy to shape: The metal bronze does not rust or corrode. Metals are subjected to the elements in industrial settings, including water, dust, filth, chemicals, and more. Iron is not the best metal to use for everything. When this void needs to be filled, Bronze is a great option. The metal is malleable and has a longer lifespan due to its resistance to rust.

Disadvantages of Bronze

Cost: Bronze exhibits a higher cost in comparison to brass and steel, yet it remains less costly than nickel-base alloys. This can be attributed primarily to its high concentration of copper.
Deterioration: Bronze exhibits limited resistance to ammonia, ferric compounds, and cyanides. Dirt and dust have the potential to erode the surface of the object. The presence of acid in bird-like waste products, as well as the concentrations of chemical agents found in animal waste, contribute to the process of corrosion and deterioration in protected regions of bronze structures. The primary factor contributing to deterioration is the interaction between sulfur and chlorine in a humid environment.
Disease: Small, pale green, rough spots that emerge suddenly on a bronze object are an early indication of Bronze Disease. Hydrochloric acid is produced when oxygen and chloride react in water, causing a disease analogous to rust in iron-based metals. The bronze is corroded because the acid creates copper and tin chlorides. The bronze will be destroyed if the process is allowed to continue unchecked.
Soft metal: Due to its inherent softness, bronze is not conducive to the production of robust weaponry. Furthermore, it exhibits poor edge retention. In the context of the Bronze Age, it was common practice to employ bronze swords primarily for thrusting purposes. However, it was observed that the tips of these swords would often deform upon impact, necessitating subsequent straightening.

Application of Bronze

Although steel and aluminum are more commonly thought of when discussing metal manufacturing, bronze is an excellent choice for a number of applications. Many other types of products can benefit from bronze’s versatility, including bronze casting, building construction, musical instruments, bronze wool, sculptures, tools, and many more. This alloy has a wide variety of potential applications, from automotive components to mechanical engineering.

Small parts: Due to its corrosion resistance, high strength, and distinctive color, bronze possesses versatile applications in the production of various small components, such as coins, furniture trim, marine hardware, automobile parts, hardware mounts, and springs. Bronze exhibits a notable resistance to corrosion in both saltwater and freshwater environments, rendering it a valuable selection for various applications such as engine components, propellers, pumps, and bells.
Architecture: Bronze can be employed by architects in the construction of various structures, particularly in cases where the intention is to maintain the alloy’s inherent or initial aesthetic appearance. One illustrative example is the extensive utilization of bronze as a material for fabricating diverse components of bridges. In order to inhibit the oxidation process of bronze, it is possible to preserve the material’s original appearance through techniques such as oiling, polishing, or the application of a specialized lacquer.
Instruments: Due to the inherent durability and distinctive timbre characteristics of bronze, it is a favored material choice among manufacturers for the production of musical instruments such as bells, cymbals, and saxophones. Bronze is a viable material for the windings of nylon and steel strings in musical instruments such as guitars and pianos, as it imparts a mellower tonal quality in comparison to alternative metallic materials.
Sculptures: Bronze is utilized by artists as a medium for sculptural creation. Copper is a commonly favored metal in the field of sculpting due to its unique property of expanding prior to solidification. This characteristic facilitates the realization of intricate details within a sculpture, enabling them to be effectively brought to life. During the cooling process, bronze undergoes a contraction, which facilitates the removal of the mold.
Tools: Axes, hammers, wrenches, and mallets provide fire hazards in the workplace if they are used on combustible materials. However, bronze is a non-sparking and non-magnetic alloy, making it a popular choice for the production of a wide range of instruments to prevent accidents involving combustible or explosive materials.
Bronze Wool: Bronze wool is a great alternative to steel wool because it doesn’t scratch or stain surfaces. It is perfect for use in the building and manufacturing industries, as well as aboard boats.
Bronze Casting: Bronze casting hardens liquid alloy in a mold. Casting is hardened bronze. When casting pumps, valve stems, bearings, and bushings for engines, bronze is easy to manufacture and pour. Bronze is reliable in sliding-part applications due to its low friction and temperature resistance.

Conclusion

Bronze is an alloy composed of copper and tin. The composition of bronze exhibits variability, yet contemporary bronzes typically consist of approximately 80% copper. Various elements such as manganese, aluminum, nickel, phosphorus, silicon, arsenic, and zinc are employed in the production of diverse types of bronze, each possessing distinct advantageous characteristics. Bronzes exhibit a marginally higher level of durability in comparison to brasses, while still maintaining a commendable degree of resistance against corrosion. They are commonly utilized in situations where there is a need for both strong tensile properties and resistance to corrosion.

References

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Alavudeen, A.; Venkateshwaran, N.; Winowlin Jappes, J. T. (2006). A Textbook of Engineering Materials and Metallurgy. Firewall Media.
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