Composition and Properties of Bronze

What is Bronze?

One of the earliest metals that man is aware of is bronze. Bronze is an alloy of copper, tin, and other metals with a golden brown color. In the Bronze Age, it was the most rigid metal in use and is still a significant metal today. These bronze facts cover its composition, characteristics, and applications. Most contemporary bronze contains 88% copper and 12% tin, though compositions can vary. Manganese, aluminum, nickel, phosphorus, silicon, arsenic, or zinc may also be present in bronze.

 

 

Brass and bronze are now often used interchangeably, even though historically, bronze was an alloy of copper and tin, while brass was an alloy of copper and zinc. Now, bronze is occasionally regarded as a form of brass, and copper alloys often go by the name of brass. In general, it has been consistently seen that bronze has been defined according to its elemental composition. Museums and historical literature often use the inclusive word “copper alloy” to avoid ambiguity. Brass comes in various common varieties, including metallic red, colored brass, 330 brass, 360 brass, and 464 brass.

Origin of Bronze:

The era when bronze was the most frequently used, and hardest metal is known as the Bronze Age. The Near Eastern city of Sumer was founded in the fourth millennium BC. At least as early as the fifth millennium BC, soft copper and brittle stone were replaced by bronze. Arsenic bronze, discovered in nature or created by combining copper and arsenic ores, was the bronze used during the Bronze Age. The third millennium BC saw the introduction of tin bronze. Arsenic bronze cannot be refined safely, while tin bronze is safer, easier to cast, and more robust.

Around the same period, both China and India entered the bronze age. There were a few things made from meteoritic iron even in the Bronze Age, but iron smelting was not prevalent. The Iron Age began around 1300 BC and came after the Bronze Age. Bronze continued to be frequently utilized during the Iron Age.

Properties of bronze:

The composition and processing of bronze affect its characteristics. However, the majority of bronze has the following features:

• Brown to golden is the many hues of bronze.
• It is considered to be highly ductile.
• Typically, it is duller than brass.
• Brass and bronze both have slightly different melting points.
• Both bronze and brass metals frequently have ring-shaped surface marks.
• Bronze is a very malleable metal.
• The friction between bronze and other metals is minimal.
• Sparks don’t fly when striking bronze against a hard surface. This makes the alloy suitable for use with flammable or explosive materials.
• Bronze expands a little bit as it hardens from a melt, unlike other metals. This is ideal for casting because it ensures that the metal will fill the mould as it cools.
• When compared to cast iron, bronze is not as brittle.
• Compared to iron or steel, the alloy’s melting point is lower.
• Compared to most steels, bronze is a better heat and electricity conductor.
• Bronze oxidizes in the air and takes on a drab copper patina. However, the patina only affects the surface, shielding the metal beneath. The patina’s initial component is copper oxide, which transforms into copper carbonate over time.
• Bronze corrodes in seawater but is shielded from the air by its patina. “Bronze sickness,” or widespread corrosion, is brought on by chlorides. But bronze typically has strong seawater corrosion resistance, like copper and brass.

Mechanical Properties of Bronze:

Since material properties are intense, they are not dependent on the mass of an object and can change at any time from one location in a system to another. Studying materials’ structures and connecting them to their properties is the focus of materials science (mechanical, electrical, etc.). Because they possess desirable combinations of mechanical properties, materials are commonly chosen for usage in various applications. Material qualities are essential for structural applications, and they must be taken into account.

 

 

Strength of Bronze:

According to the mechanics of materials, a material’s strength is its capacity to sustain an applied load without failing or deforming plastically. The link between the external loads placed on a material and the ensuing deformation or change in the material’s dimensions is considered when determining a material’s strength. A material’s strength is determined by its capacity to bear this applied load without breaking down or deforming plastically.

The Ultimate tensile strength:

Aluminum bronze, UNS C95400, has a maximum tensile strength of roughly 550 MPa.

Tin bronze, often known as gun metal UNS C90500, has a maximum tensile strength of roughly 310 MPa.

About 1380 MPa is the maximum tensile strength of copper beryllium, UNS C17200.

The ultimate tensile strength is the highest value on the typical stress-strain curve. This is equivalent to the maximum stress that a structure in tension can withstand. If this stress is applied and maintained, a fracture will occur; ultimate tensile strength is frequently abbreviated as “tensile strength” or “the ultimate.” This value often exceeds the yield stress by a large margin (as much as 50 to 60 percent more than the yield for some metals). A ductile material experiences necking, a localized reduction in cross-sectional area, when it reaches its maximum strength. The ultimate strength is the highest stress on the stress-strain curve. Even though deformations may keep growing, the pressure typically diminishes once the total strength is reached. Since it is an intense property, the size of the test specimen has no bearing on how valuable it is. However, it also depends on other elements, including how the sample was prepared, whether or not there are surface flaws, and how hot the test environment and object are. Aluminum has an ultimate tensile strength of 50 MPa, while very high-strength steel has a tensile strength of up to 3000 MPa.

Yield Strength of Bronze:

Aluminum bronze, UNS C95400, has a yield strength of roughly 250 MPa.

Tin bronze, often known as gun metal UNS C90500, has a yield strength of approximately 150 MPa.

Copper beryllium, UNS C17200, has a yield strength of around 1100 MPa.

The yield point on a stress-strain curve is where elastic activity ends, and plastic behavior starts. The material property known as yield strength or yield stress is the tension at which a material begins to distort plastically. However, nonlinear (elastic + plastic) deformation begins at the yield point. The material will deform before the yield point and resume its original shape once the applied load is eliminated. Some portion of the deformation will become permanent and irreversible once the yield threshold is passed. The yield point phenomenon is displayed by some steels and other materials. Low-strength aluminum has a yield strength of 35 MPa, while high-strength steel has more than 1400 MPa.

Young’s Modulus of Elasticity:

Aluminum bronze, UNS C95400, has an elastic Young’s modulus of roughly 110 GPa.

Tin bronze, UNS C90500, and gunmetal have an elastic Young’s modulus of elasticity of around 103 GPa.

Copper beryllium, UNS C17200, has an elastic Young’s modulus of 131 GPa.

Young’s modulus of elasticity is typically determined by tensile testing and is the elastic modulus for tensile and compressive stress in the linear elasticity regime of uniaxial deformation. A body can regain its proportions after removing the load to a specific stress level. The atoms in a crystal migrate from their equilibrium position due to the applied stresses, but they all move in the same direction and preserve their relative geometry. When the tensions are eliminated, there is no permanent deformation since all the atoms return to their original locations. Hooke’s law states that the stress (in the elastic zone) is proportional to the strain, and Young’s slope is the modulus.

The hardness of Bronzes:

Aluminum bronze, UNS C95400, has a Brinell hardness of roughly 170 MPa. The amount of aluminum (and other alloys) and the stresses brought on by cold working increase the hardness of aluminum bronzes.

Tin bronze, UNS C90500, and gunmetal have a Brinell hardness of roughly 75 BHN.

Copper beryllium, UNS C17200, has a Rockwell hardness of about 82 HRB.

One of the most used indentation hardness tests created for hardness testing is the Rockwell hardness test. The Rockwell tester examines the depth of penetration of an indenter under a heavy load (significant load) compared to the penetration made by a preload, in contrast to the Brinell test (minor load). The primary load is applied and released while preserving the little load, which establishes the zero position. The Rockwell hardness value is determined by comparing the penetration depth before and after the primary load is applied. In other words, the hardness and depth of penetration can be said to be inversely related. Rockwell hardness has a straightforward display of hardness levels as its primary benefit. A result is a dimensionless number represented by the letters HRA, HRB, HRC, etc., where the final letter denotes the relevant Rockwell scale.

A Brale penetrator (120° diamond cone) and the main load of 150kg are used in the Rockwell C test.

Thermal Properties of Bronzes:

Materials’ thermal characteristics describe how they react to temperature variations and heat application. A solid’s temperature increases and its size expands due to the heat it absorbs. However, the way various materials respond to heat application varies.

In the actual use of solids, heat capacity, thermal expansion, and thermal conductivity are frequently crucial.

Melting Point of Bronzes:

Around 1030°C is the melting temperature of UNS C95400, aluminum bronze.

Tin bronze, often known as gun metal UNS C90500, has a melting point of roughly 1000°C.

Around 866°C is the melting temperature of copper beryllium or UNS C17200. Melting, in general, is the transition of a substance from its solid state into its liquid form. The temperature at which this phase change occurs is known as a substance’s melting point. The melting point specifies a circumstance under which an equilibrium between a solid and a liquid is possible.

Thermal Conductivity of Bronzes:

The aluminum bronze’s UNS C95400 thermal conductivity is 59 W/m (m. K).

Tin bronze, also known as UNS C90500 gunmetal, has a thermal conductivity of 75 W/m (m. K).

The copper beryllium UNS C17200’s thermal conductivity is 115 W/m (m. K).

The thermal conductivity, k (or ), measured in W/m.K, is used to determine how well solid materials transport heat. It evaluates a material’s capacity to conduct heat via material. It is essential to remember that all matter is subject to Fourier’s law, regardless of its state (solid, liquid, or gas). Consequently, it is defined as both liquids and gases.

Most liquids and solids’ thermal conductivity varies with temperature and vapors; it also relies on pressure.

Composition of Bronze:

Around 88% of bronze is composed of copper, 12% being tin and other metals (such as aluminum, zinc, nickel, manganese, and lead), and occasionally additional metalloids or nonmetals (arsenic, silicon, and phosphorus).

Uses of Bronze:

Due to its low frictional qualities, bronze is used in bearings, musical instruments such as guitar strings, other electrical contacts, and ship propellers. In woodworking, bronze wool is preferred to steel wool since it doesn’t stain oak. Architectural industry products include stair railings, mailboxes, window frames, decorative classing, bearings, and bells.

Bronze wool is an alternative to steel wool that doesn’t shed metal threads that could result in shorts and sparks. Oil industry as components of oil rigs. Electrical connections and connectors, small electric motors, and the electronic industry. Pumps, valve stems, and automotive transmissions are examples of industrial castings. Architectural elements in the marine industry, such as hulls, pumps, engine components, and propellers

Coins have been produced from bronze. Most so-called “copper” coins are bronze, made of copper, 4% tin, and 1% zinc.

Since ancient times, bronze has been used to create sculptures. Sennacherib, king of Assyria (706–681 BC), asserted that he was the first to develop massive bronze statues using two-part moulds, while sculptures were produced using the lost-wax technique long before this.

Medals, mirrors, safety equipment (hammers, mallets, wrenches), screws, and springs are further applications.

Different Bronze alloys:

Metallurgists categorize bronze alloys based on their chemical makeup. Here are a few typical alloys:

Aluminum bronze:

The aluminum, iron, and nickel percentages in aluminum bronze range from 6% to 12%. It is a sturdy alloy with superior wear and corrosion resistance. The ideal alloy for pumps, valves, and other hardware exposed to corrosive fluids is aluminum bronze.

Cupronickel:

A bronze alloy with 2% to 30% nickel is known as cupronickel or copper-nickel. The alloy exhibits strong thermal stability and resistance to corrosion, especially in steam or wet air. In seawater, it is also superior to other kinds of bronze. Ship hulls, pumps, valves, electronics, and marine gear are among the applications for cupronickel.

Nickel-Silver:

Despite its popular name, nickel silver doesn’t actually contain any silver. Its silvery hue is how it got its name. Zinc, nickel, and copper are all present in nickel and silver. It has fair corrosion resistance and is moderately strong. Dinnerware, decorations, optical devices, and musical instruments employ nickel silver.

Phosphor bronze (tin bronze):

Tin bronze, often known as phosphor bronze, comprises 0.01% to 0.035% phosphorus and 0.5% to 1.0% tin. This alloy has a fine grain, a low coefficient of friction, and a high fatigue resistance, in addition to being durable and robust. Bellows, washers, electrical equipment, and springs are among the things that use phosphor bronze.

 

 

Silicon bronze:

Red silicon bronze and red silicon brass are both components of silicon bronze. Red bronze has less zinc than red brass, which has 20% zinc and 6% silicon. Lead content is low in silicon bronze, which may contain manganese, tin, or iron. Silicon bronze is solid and resistant to corrosion. Pumps and valve stems are made of it.

 

 

Manganese Bronze:

Copper, zinc, aluminum, iron, and up to 3% manganese make up manganese bronze. It is resilient to shock and deforms as opposed to breaking. It is frequently used in boat propellers because of its excellent resistance to seawater corrosion. In addition, gears, nuts, and bolts are made of manganese bronze.

Bearing Bronze:

Lead is present in bearing bronze in amounts between 6 and 8%. Its lower friction due to the higher lead concentration makes it beneficial in high-wear applications, particularly in locations that are challenging to access or maintain. Bearing bronze is most frequently used to create bushings and bearings, as its name suggests.

Bismuth Bronze:

There is 1 to 6% bismuth in bismuth bronze. It is more flexible, highly corrosion-resistant, and thermally conductive. It polishes nicely; therefore, mirrors and light reflectors occasionally utilize it. Bearings are used in industrial settings the most frequently. However, historically, it has been utilized as kitchenware. It is now sometimes used in place of leaded bronze.

Difference between Bronze and Brass:

According to contemporary definitions, bronze is an alloy of copper and tin, whereas brass is an alloy of copper and zinc. It hasn’t always been easy to tell the two alloys apart. The Italian word bronze, which means “bell metal or brass,” has roots in an ancient Persian word for brass. In actuality, the term “bronze” is derived from the French word bronze, derived from the Italian word bronze. Due to their various compositions, older artefacts are better described as “copper alloys.”

How to select the suitable Metal Alloy:

Designing and producing a high-quality part or product depends on selecting the appropriate type of metal for the application. Although copper, brass, and bronze offer strength, corrosion resistance, and electrical and thermal conductivity, there are clear distinctions between the three metals. When choosing sheet metal materials, it’s essential to keep in mind some significant differences, such as:

The three metals are all strong, but they don’t all have the same degree of flexibility. The highest degree of ductility, conductivity, and flexibility is provided by pure oxygen-free copper. Copper is very malleable and has excellent conductivity, although bronze and brass are easier for the machine.

General usefulness The material most frequently regarded as ideal for general uses is brass. It is pliable, cheap, simple to cast, and low-friction. It can be applied to decorative elements, often touched metal objects (like doorknobs), and food-grade surfaces that require antibacterial or antimicrobial properties.

The corrosion resistance of tools and equipment designed for marine conditions must be pretty good. The finest material for preventing corrosion in saltwater and marine conditions is bronze. It can resist the strain of marine applications thanks to its toughness and durability.