The bronzes are a family of copper-based alloys traditionally alloyed with tin but can refer to alloys of copper and other elements (e.g., aluminum, silicon, and nickel). Bronzes are somewhat stronger than the brasses, yet they still have a high degree of corrosion resistance. Generally, they are used when good tensile properties are required in addition to corrosion resistance. For example, beryllium copper attains any copper-based alloy’s greatest strength (1,400 MPa).
Historically, alloying copper with another metal, for example, tin, to make bronze was first practiced about 4000 years after the discovery of copper smelting and about 2000 years after “natural bronze” had come into general use. An ancient civilization is defined in the Bronze Age as producing bronze by smelting its copper and alloying it with tin, arsenic, or other metals. Bronze, or bronze-like alloys and mixtures, were used for coins over a longer period. Bronzes are still widely used for springs, bearings, bushings, automobile transmission pilot bearings, and similar fittings and are particularly common in small electric motors’ bearings. Brass and bronze are common engineering materials in modern architecture and are primarily used for roofing and facade cladding due to their visual appearance.
The aluminum bronzes are a family of copper-based alloys that combine mechanical and chemical properties unmatched by any other alloy series. They contain about 5 to 12% of aluminium. In addition, aluminium bronzes also contain nickel, silicon, manganese, and iron. They have excellent strength, similar to low alloy steels, and excellent corrosion resistance, especially in seawater and similar environments, where the alloys often outperform many stainless steels. Their excellent resistance to corrosion results from the aluminium in the alloys, which reacts with atmospheric oxygen to form a thin, tough surface layer of alumina (aluminium oxide) which acts as a barrier to corrosion of the copper-rich alloy. They are found in wrought and cast form. Aluminium bronzes are usually golden in color. Aluminium bronzes are used in seawater applications that include:
- General sea water-related services
- Pipe fittings
- Pumps and valve components
- Heat exchangers
Properties of Aluminium Bronze
Material properties are intensive properties, which means they are independent of the amount of mass and may vary from place to place within the system at any moment. Materials science involves studying materials’ structure and relating them to their properties (mechanical, electrical, etc.). Once materials scientist knows about this structure-property correlation, they can then go on to study the relative performance of a material in a given application. The major determinants of the structure of a material and thus of its properties are its constituent chemical elements and how it has been processed into its final form.
Mechanical Properties of Aluminium Bronze
Materials are frequently chosen for various applications because they have desirable combinations of mechanical characteristics. For structural applications, material properties are crucial, and engineers must consider them.
Strength of Aluminium Bronze
In the mechanics of materials, the strength of a material is its ability to withstand an applied load without failure or plastic deformation. The strength of materials considers the relationship between the external loads applied to a material and the resulting deformation or change in material dimensions. The strength of a material is its ability to withstand this applied load without failure or plastic deformation.
Ultimate Tensile Strength
The ultimate tensile strength of aluminium bronze – UNS C95400 is about 550 MPa.
The ultimate tensile strength is the maximum on the engineering stress-strain curve. This corresponds to the maximum stress sustained by a structure in tension. Ultimate tensile strength is often shortened to “tensile strength” or “the ultimate.” If this stress is applied and maintained, a fracture will result. Often, this value is significantly more than the yield stress (as much as 50 to 60 percent more than the yield for some types of metals). When a ductile material reaches its ultimate strength, it experiences necking where the cross-sectional area reduces locally. The stress-strain curve contains no higher stress than the ultimate strength. Even though deformations can continue to increase, the stress usually decreases after achieving the ultimate strength. It is an intensive property; therefore, its value does not depend on the size of the test specimen. However, it depends on other factors, such as the specimen preparation, the presence or otherwise of surface defects, and the temperature of the test environment and material. Ultimate tensile strengths vary from 50 MPa for aluminum to as high as 3000 MPa for very high-strength steel.
The yield strength of aluminium bronze – UNS C95400 is about 250 MPa.
The yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning plastic behavior. Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically. In contrast, the yield point is the point where nonlinear (elastic + plastic) deformation begins. Before the yield point, the material will deform elastically and return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible. Some steels and other materials exhibit a behavior termed a yield point phenomenon. Yield strengths vary from 35 MPa for low-strength aluminum to greater than 1400 MPa for high-strength steel.
Young’s Modulus of Elasticity
Young’s modulus of elasticity of aluminium bronze – UNS C95400 is about 110 GPa.
Young’s modulus of elasticity is the elastic modulus for tensile and compressive stress in the linear elasticity regime of a uniaxial deformation and is usually assessed by tensile tests. Up to limiting stress, a body will be able to recover its dimensions on the removal of the load. The applied stresses cause the atoms in a crystal to move from their equilibrium position, and all the atoms are displaced the same amount and maintain their relative geometry. When the stresses are removed, all the atoms return to their original positions, and no permanent deformation occurs. According to Hooke’s law, the stress is proportional to the strain (in the elastic region), and the slope is Young’s modulus. Young’s modulus is equal to the longitudinal stress divided by the strain.
The hardness of Aluminium Bronze
Brinell hardness of aluminium bronze – UNS C95400 is approximately 170 MPa. The hardness of aluminum bronzes increases with aluminum (and other alloys) content and stresses caused by cold working.
Rockwell hardness test is one of the most common indentation hardness tests developed for hardness testing. In contrast to the Brinell test, the Rockwell tester measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). The minor load establishes the zero position, and the major load is applied, then removed while maintaining the minor load. The difference between the penetration depth before and after application of the major load is used to calculate the Rockwell hardness number. That is, the penetration depth and hardness are inversely proportional. The chief advantage of Rockwell hardness is its ability to display hardness values directly. The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last letter is the respective Rockwell scale.
The Rockwell C test is performed with a Brale penetrator (120°diamond cone) and a major load of 150kg.
Thermal Properties of Aluminium Bronze
Thermal properties of materials refer to the response of materials to changes in their temperature and the application of heat. As a solid absorbs energy in the form of heat, its temperature rises, and its dimensions increase. But different materials react to the application of heat differently.
Melting Point of Aluminium Bronze
The melting point of aluminium bronze – UNS C95400 is around 1030°C.
In general, melting is a phase change of a substance from the solid to the liquid phase. The melting point of a substance is the temperature at which this phase change occurs. The melting point also defines a condition where the solid and liquid can exist in equilibrium.
Thermal Conductivity of Aluminium Bronze
The thermal conductivity of aluminium bronze – UNS C95400 is 59 W/(m. K).
The heat transfer characteristics of solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It measures a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies to all matter, regardless of its state (solid, liquid, or gas). Therefore, it is also defined for liquids and gases.
The thermal conductivity of most liquids and solids varies with temperature, and for vapors, it also depends upon pressure. In general:
Most materials are nearly homogeneous. Therefore we can usually write k = k (T). Similar definitions are associated with thermal conductivities in the y- and z-directions (ky, kz). However, for an isotropic material, the thermal conductivity is independent of the transfer direction, kx = ky = kz = k.