Aluminum bronze is a type of copper alloy in which aluminum is the primary alloying element added to the copper. This stands in contrast to standard bronze or brass, in which the alloying elements are tin and zinc, respectively. Aluminum enhances copper by imparting oxidation resistance in the form of a thin, tightly adherent aluminum oxide film. Other metals such as manganese, nickel, silicon, and iron can be added to aluminum bronze to further enhance strength or anti-corrosive properties.
The manufacturing process for creating aluminum bronze is similar to the techniques involved for other copper alloys. First, the copper element is heated to a predetermined temperature. Once the copper is in its molten state, specified amounts of aluminum are added (in addition to other alloying elements, which will depend on the type of alloy desired). The molten mixture is then poured into the mold for the specific component and allowed to cool.
[b]Types of Aluminum Bronze[/b]
There are numerous types of aluminum bronze as categorized by the Unified Numbering System (UNS), developed by American Society for Testing and Materials (ASTM) and Society of Automotive Engineers (SAE). These alloys differ mainly based on the amount of primary element (aluminum) and the number of secondary elements alloyed with the copper.
The various types of aluminum bronze are defined in the UNS using reference numbers ranging from C95200 to C95800. For instance, C95200 aluminum bronze contains 8.5% to 9.5% aluminum by weight, while C95300 contains 9.0% to 11.0%
Although there are dozens of aluminum bronze alloys available, they can all be classified into four principal types:
- Low-alloy, single-phase alloys — These alloys contain less than 8% aluminum and have excellent cold ductility properties, making them ideal for cold working into tubes, strips, sheets, and wires.
- Moderately alloyed, two-phase (duplex) alloys — These alloys contain 8% to 11% aluminum and small amounts of other elements added for higher strength properties. These materials are suitable for hot working applications. Aluminum bronze casting is also a popular method for working these alloys.
- Copper-aluminum-silicon alloys, or silicon-aluminum bronzes — These alloys contain up to 6% aluminum and 2% silicon. Similar to other bronzes, these materials have low magnetic permeability as well as exceptional resistance to shock and vibrational loading.
- Copper-manganese-aluminum alloys, or manganese-aluminum bronzes — Unlike other aluminum bronzes, manganese is the primary alloying element by weight (approximately 13%) in these materials, while aluminum makes up about 8% to 9%. Although these alloys do not possess the same strength properties as the other types, they have excellent resistance to impingement, cavitation, and wear.
[b]Common Uses for Aluminum Bronze[/b]
Thanks to its desirable mechanical properties, superior corrosion resistance, and high castability and machinability, aluminum bronze is used in a wide range of applications. Some typical applications include:
- General seawater-related service — The oxide film produced by aluminum bronze imbues it with exceptional corrosion resistance in seawater environments. The material’s wear and erosion resistance also make the material suitable for impellers, propellers, and other marine hardware.
- Water supply — The corrosion resistance of aluminum bronze can be highly beneficial for components used in the water treatment and supply industry, in which corrosion is always a major concern.
- Oil and petrochemical industries — Aluminum bronze is also known for its non-sparking characteristics. This attribute is especially useful for parts and components used in the oil and gas industry, in which the surrounding atmosphere may contain explosive or ignitable gas, vapor, or dust.
- Specialized anti-corrosive applications — This alloy can also be used in aggressive, corrosive environments that would be otherwise unsuitable for other copper alloys such as brass. Aluminum bronze is also resistant to biofouling in saline waters.
- Certain structural retrofit building applications — The unique properties of aluminum bronze make it able to withstand heavy loads, shock, and vibrational load. This makes the material ideal for bearings in bridges and base isolation systems in buildings for seismic retrofitting applications.
[b]Working With Aluminum Bronze[/b]
Aluminum bronze comes in many different compositions, with each alloy offering unique properties for various applications. Whether working with aluminum bronze 954 or 958, high corrosion resistance and superior mechanical properties make these materials a go-to choice for a wide range of demanding environments.