Bronze Characteristics
Bronze alloys can be red or yellow depending on its composition, the main difference between bronzes and brass is that bronze is opaque.
It is one of the most malleable metals used for a variety of applications including artwork, tubing, sculptures, heat-exchanger platers, and many others.
Machinability, formability, die casting, rolling, sheet-metal fabrication, and extrusion are some of its common applications.
An oxidation mechanism prevents further corrosion of bronze alloys when in contact with oxygen. The created layer not only protects but changes its color into green or blue depending on the alloy, providing an antique appearance.
The density is around 10% higher than steel, but its thermal, mechanical, and electrical properties are excellent.
Bronze Alloys And Their Manufacturability
As well as other copper alloys, bronze variations are designated by the UNS numbers.
Bronze composed of a majority of copper and tin is known as phosphor bronze. Other bronze variations depend on the substitution of tin as an alloying element replacing it with aluminum and silicon.
Additional elements such as manganese, nickel, and iron are also used. These alloying elements provide an improvement of the mechanical properties. However, since copper is a soft material, machinability is not affected.
1. Aluminum Bronze UNS C95400
Composed of 83% copper, 10 to 11,5% aluminum, 2,5% nickel, and minor quantities of iron, manganese, and other alloying elements.
This alloy has excellent wear resistance, as well as considerable strength and ductility and it can be heat-treated to increase its mechanical properties.
UNS C95400 has excellent machinability and it can also be cast, extruded, and fabricated as sheet-metal.
Common applications of this alloy include pump impellers, bearings, gears, pinions, and bushings.
√ Manufacturing Processes Performance
| Tensile Ultimate Strength | Tensile Yield Strength | Hardness | Fatigue Strength | Density | Melting point |
|---|---|---|---|---|---|
| 615MPa | 225 MPa | 170 HB | 240 MPa | 7,45 g/cc | 1025-1040°C |
√ Mechanical Properties
| Machinability | Formability | Weldability | Workability | Corrosion resistance | Wear resistance |
|---|---|---|---|---|---|
| 0.6 | Good | Excellent | Good | Excellent | Excellent |
2. Phosphor Bronze UNS C52400 H04
This is a fully hardened bronze alloy containing up to 90% copper, 8 to 10% tin, and small amounts of phosphorus, zinc, lead, and iron.
Although its density is higher than that of other bronze alloys, its mechanical properties, corrosion resistance, formability, and workability are excellent. Its low melting point allows it to be used in cast applications.
Used for bushings, fittings, expansion plates, as well as other applications in which wear, corrosion, and fatigue resistance is required
√ Manufacturing Processes Performance
| Tensile Ultimate Strength | Tensile Yield Strength | Hardness | Fatigue Strength | Density | Melting point |
|---|---|---|---|---|---|
| 670MPa | 550 MPa | 224 HB | 280 MPa | 8,78 g/cc | 845-950°C |
√ Mechanical Properties
| Machinability | Formability | Weldability | Workability | Corrosion resistance | Wear resistance |
|---|---|---|---|---|---|
| 0.3 | Very Good | Very good | Very Good | Excellent | Excellent |
3. Silicon Bronze UNS C65500 H04
UNS C65500 is a high silicon bronze, with a composition of between 2,8 and 3,8% silicon, up to 95% copper, less than 1,5% zinc and manganese, and smaller amounts of iron, nickel, and lead to improving machinability.
It combines the corrosion resistance of copper-based any material, with excellent workability and formability.
Manufacturing processes include extrusion, forging, pressing, and sheet-metal fabrication. Even though its machinability is not the best for these alloys, machining at low speeds with proper coolant flow is required.
Applications include hydraulic pressure lines, bolts, pressurized fluid lines, electrical conduits, and heat-exchanger tubing.
√ Manufacturing Processes Performance
| Tensile Ultimate Strength | Tensile Yield Strength | Hardness | Fatigue Strength | Density | Melting point |
|---|---|---|---|---|---|
| 630 MPa | 370 MPa | 88 HRB | 200 MPa | 8,6 g/cc | 970-1025°C |
√ Mechanical Properties
| Machinability | Formability | Weldability | Workability | Corrosion resistance | Wear resistance |
|---|---|---|---|---|---|
| 0.3 | Excellent | Good | Excellent | Excellent | Very Good |
Surface Finishing For Bronze
Metals need a finishing process to guarantee their durability and proper performance. Bronze is not the exception. However, bronze is very resistant by itself. These finishes are recommended only for special applications.
1. Polishing
A polished surface is further protected from corrosion and develops a more appealing appearance. Bronze is polished both manually and automatically using cotton fibers.
2. Surface painting
This technique is used to increase the impact resistance by providing a damping layer that will protect the material’s surface from the environment.
3. Chemical surface finishing
The idea behind this finishing method is to accelerate the creation of the colored oxide layer that protects bronze from corroding. It not only protects from corrosion but provides an antique look.
Bronze Materials: Design And Engineering Tips
Bronze alloys are used since centuries ago, and they’ve proven to be versatile due to their impressive properties. Its easy manufacture combined with the inherent corrosion resistance of copper creates material suitable for almost every manufacturing process.
Here are some tips to help you with your designs:
1. Even though bronze is a dense material, its thermal properties are incredible compared with other metals. Extruded bronze profiles for heat-exchangers are a useful application.
2. Aluminum bronzes are lighter. If your application requires saving in weight, these alloys are strong and lightweight compared with other copper alloys.
3. Copper extraction and recycling is a cheap and fast process due to its low melting points. Since bronze is made primarily from copper, it has a low price.