What is Manganese Bronze?
Manganese Bronze is more than just one type of metal – through research and innovation, it has now become an invaluable class of copper alloys that provide unique material properties. There are now many types of bronze in a supplier’s stock, and this can pose an interesting challenge: which bronze is the best fit for your application? This article will help answer this question by detailing one of the many bronzes found in our article on the types of bronzes, that being the manganese bronzes. Through an investigation of the strengths, weaknesses, and properties of this material, this article aims to show where manganese bronze should be specified and how it has become one of the stronger copper alloys of the modern age.
Physical Properties of Manganese Bronze
Pie chart showing the relative composition of elements in Manganese Bronze.
Figure 1: Qualitative breakdown of manganese bronze.
Note the small amount of manganese and the even smaller amount of tin.
Figure 1 shows a visualization of the constituent metals within manganese bronze. Below is a quantitative breakdown of a specific manganese bronze (UNS C86300 alloy), to provide an idea of alloying elements by weight:
60 – 68 % Copper
25 % Zinc
3.0 – 7.5 % Aluminum
2.5 – 5.0 % Manganese
2.0 – 4.0 % Iron
≤ 0.20 % Tin
Some amount of lead may also be present, but manganese bronze always has a high amount of zinc and a relatively small amount of manganese and tin (for this reason it is sometimes referred to as a form of brass, but there is much overlap). The density of manganese bronze is around 7.7 g/cm3, and it is a yellow-brown brass color that patinas with age. Most alloys designated as manganese bronzes are non-heat treatable but are exceptionally strong despite not responding to strengthening procedures. It is non-magnetic and has around 80% of the electrical conductivity of pure copper, as well as being corrosion and wear-resistant. It is difficult to braze, solder, oxyacetylene weld, gas shield arc weld, and carbon arc weld, but can be coated-metal arc welded. It is generally difficult to machine but can be leaded to respond better to machining stresses.
Resistances and weaknesses
Manganese bronze is often specified over other bronzes for its exceptional longevity. It can withstand wear and corrosion better than most other bronzes thanks to its added manganese, and while not heat treatable, it boasts an impressive strength profile. It is resistant to seawater corrosion (though less so than silicon bronzes), and is both hot forgeable and castable, if desired. Its main disadvantage is its price tag, as it is one of the more complex bronzes to fabricate. Also, it must be reliably lubricated to work optimally, as abrasive conditions will weaken the alloy’s integrity.
Mechanical Properties for Manganese Bronze
Table 1 below shows a summary of useful mechanical properties of manganese bronze – this section will discuss each value and how it relates to the applications of this copper alloy.
Table 1: Summary of mechanical properties for manganese bronze – note that these values come from a summary of popular alloys and are subject to variability.
Mechanical Properties
Metric
English
Tensile yield strength
460 MPa
66700 psi
Modulus of Elasticity
105 GPa
15200 ksi
Fatigue Strength
170 MPa
24700 psi
Hardness (Rockwell B)
65
Machinability
8-30%
Manganese bronze is primarily specified for its strength, and this claim is supported by its tensile yield strength. This parameter describes how much stress it takes to permanently deform, or “yield”, a specimen of material in tension, but in practice, it is often used as a measure of how strong a material is. Manganese bronze has an impressive yield strength of 460 MPa, which surpasses some aluminum alloys and even some low-carbon steels. This strength combined with its corrosion resistance gives manganese an advantage over traditional alloys and allows it to function in more applications as a result.
The modulus of elasticity describes a material’s internal strength and how likely it will return to its original shape under increasing stress. It is a counterintuitive value because, as the modulus of elasticity of a material increases, its stretchiness decreases- that is, the material will retain its shape even if pulled, pushed, or bent. Manganese bronze has a decently high elastic modulus of 105 GPa, making it half as resistant to deformation as most steels, but also more formable as a result. While manganese bronze is difficult to weld, it can be formed and manipulated into shape, reducing the need for joining and machining.
Manganese bronze is highly wear-resistant, meaning that it will keep its strength profile over a long period of time; this property is thanks to its impressive fatigue strength, a measure of how a material performs under cyclic loading conditions. Some materials are strong but can be weakened due to micro-cracking formed by repeated use, and so their fatigue strength is considered low (note that this value is always lower than the yield strength, meaning stress under this threshold can still damage a material). Manganese bronze is celebrated for its ability to withstand cyclic loading conditions, and its fatigue strength of 170 MPa shows why it is most often used in aerospace, fastener, marine, and oil & gas industries, as parts must stay strong despite jarring, repetitive stress.
The hardness of a material describes its tendency to locally deform on its surface, or to scratch, etch, pit, or dent. It is calculated by passing many materials through a standardized hardness indenter machine and then rating these materials on a comparative scale with each other. The value found in Table 1 is from the Rockwell B hardness scale, which is used to describe the hardness of many alloys (more scales exist, but for ease of reading we will only show the Rockwell B scale values). To get an idea of the hardness of manganese bronze, pure copper has a Rockwell B hardness of around 50. This comparison shows that, while strong and durable, manganese bronze will easily scratch in the presence of a harder material. Therefore, manganese bronze must be either well lubricated and/or used in non-abrasive applications, as surface deformation can introduce weakness into the material and increase the risk of part failure.
There are downsides to being exceptionally strong, and this is the case when talking about machinability. This value is a comparative measure of how a material responds to machining stresses (think milling, turning, drilling, etc.), and is reported as a percentage value. There exists for each alloy class a designated material that is considered easy to machine and is given a machinability score of 100% (for bronzes, this material is UNS C36000 free cutting brass). Any percentage below 100% means the material is more difficult to machine, and as the percentage gets lower so does the ability to tool the metal; it should be clear from this explanation that manganese bronze is not the ideal machining material with a score of 8-30%. While lead can be added to amend this issue, manganese bronze should generally not be specified if machining is imperative, as it will reduce tool life and overall cause grief for the machinist.
Applications of Manganese Bronze
As previously explained, manganese bronze finds many uses in the oil & gas, marine, aerospace, steel, pulp, and other industries. Below are some examples of specific manganese bronze applications but note that many more exist depending on where you look.
Some common applications include:
Welding rods
Fasteners and bolts
Gears
Slow-speed heavy load bearings
Cams
Landing gear parts
and more.
If manganese bronze looks appealing for your project, contact your supplier and they can find you the right alloy for the job. They will have the most recent alloys and information regarding this material, as well as possible alternatives if you cannot find the right metal.
Summary
This article presented a brief summary of the properties, strength, and applications of manganese bronze. For information on other products,please visit XTJ.
XTJ is a leading OEM Manganese Bronze Manufacturer that is dedicated to providing one-stop manufacturing solutions from prototype to production. We are proud to be an ISO 9001 certified system quality management company and we are determined to create value in every customer relationship. We do that through collaboration, innovation, process improvements, and exceptional workmanship.