Magnesium alloys are materials made from a mixture of magnesium and other metals conferring superior mechanical properties. This makes them suitable for use as structural components. For specific applications, heat treatment methodologies are used to modify these properties to obtain a desirable combination that improves performance.
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In this article, we discuss what magnesium alloys are, their properties, the role of heat treatment in improving their performance, applications of biodegradable magnesium alloys, and finally an outlook on the magnesium alloy industry.
What are magnesium alloys and their uses?
A magnesium alloy is a material obtained from the mixture of magnesium with other metals under special conditions. Magnesium is the lightest structural metal with low density, but when coupled with either one or more of zirconium, aluminum, zinc, or manganese, its strength, resistance to pressure, and castability are significantly improved.
Biodegradable magnesium alloys have applications in bone engineering and stents. They are used as temporary implant materials in tissue engineering because they do not require a second surgery for their removal. Also, they are very strong and lightweight which makes them ideal for use in devices, planes, cars, etc.
High-tech medical device companies like AAP Implantate in Germany produce state-of-the-art resorbable magnesium alloys for biomedical applications. Global companies like DonGuan Eontec Co., Ltd also provide magnesium alloy technologies as an important part of their portfolios.
Magnesium alloy also makes up a huge proportion of the materials used for making Apple’s MacBooks.
What are the properties of biodegradable magnesium alloy?
Biodegradable magnesium alloy have three key properties:
- High strength-to-weight ratio
- Easily degradable in biological environments but limited by rapid corrosion properties
- When used in vivo there is little or no toxicity and a response from the system. Rather, it helps to stimulate bone growth and has antibacterial and antitumor effects, as well as anti-inflammatory effects. It does have the advantage that it is a necessary element of human metabolism.
Why subject magnesium alloys to heat treatment?
Despite the abovementioned advantages of using magnesium alloys, there are some disadvantages associated with their structure that can limit their use.
Magnesium alloys are highly prone to corrosion either by intergranular or micro galvanic corrosion, they are prone to wear because they have a soft matrix and oxide layer, have poor tensile behavior due to a soft matrix and grain size, and their high biocompatibility makes them prone to high excretion through body fluids.
As a result, to optimize their functionality, it becomes important to develop methodologies that can improve these properties without compromising on other desirable intrinsic properties or at least result in an acceptable trade-off. Amongst these methods, heat treatment is considered the most effective way to improve the properties of biodegradable magnesium alloy.
What change does heat treatment cause in biodegradable magnesium alloys?
The properties of biodegradable magnesium that are affected by heat treatment include their mechanical properties and corrosiveness through changes in their microstructure.
A study in the Journal of Alloys and Compounds showed that heat treatment can affect the microstructure and mechanical properties of Al-Si-Mg cast alloys through spheroidization, fragmentation, and coarsening. Therefore, heat treatment provides an avenue to enhance these properties and a suitable combination of these properties can be obtained by manipulating the heat treatment parameters.
Heat-treated biodegradable magnesium alloy is also expected to perform better overall. For example, other properties of biodegradable magnesium alloys that can be affected by heat treatment are machinability and corrosion behavior.
This was the case in a related study reported in the Journal of Magnesium and Alloys. An AZ91 magnesium alloy was heat treated and it was observed that the machinability of the alloy was improved but at the cost of losing higher resistance to corrosion. In such cases, trade-offs may be necessary in favor of the desired performance.
Heat treatments have several parameters like temperature, alloying element, processing, etc. that can be varied to improve specific properties of biodegradable magnesium alloy. As a result, to improve the desired property of magnesium alloy for use as a biodegradable structural implant, specific methodologies must be followed.
A brief review published in the Metals and Materials Journal outlines some of these methodologies applicable to specific performance objectives.
The advantage of heat treatment is that it doesn’t affect already beneficial properties like chemical composition, shape, and biodegradability but affects just the material’s microstructure. This can be achieved through either fine grain strengthening or second-phase strengthening. Some heat treatment methods used include.
- Solid solution treatment
- Aging treatment
- Solid solution + Aging treatment
What is the outlook on the use of biodegradable magnesium alloys?
The use of biodegradable magnesium alloy is growing yearly as different industries can produce different combinations of magnesium alloys to meet their needs. Recent market research by grand view research states that the global market for magnesium alloys is expected to be valued at USD 6.62 billion by 2027 growing at a 9.9% compound annual growth rate during this period.
This implies that the biodegradable magnesium alloy industry has huge potential and several opportunities.
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References and Further Reading
Chen, J., Tan, L., Yu, X., Etim, I. P., Ibrahim, M., and Yang, K. (2018). Mechanical properties of magnesium alloys for medical application: A review. Journal of the Mechanical Behavior of Biomedical Materials, 87, 68–79. https://doi.org/10.1016/j.jmbbm.2018.07.022
Hanawa, T. (2010). 1—Overview of metals and applications. In M. Niinomi (Ed.), Metals for Biomedical Devices (pp. 3–24). Woodhead Publishing. https://doi.org/10.1533/9781845699246.1.3
Mohammadi Zerankeshi, M., Alizadeh, R., Gerashi, E., Asadollahi, M., and Langdon, T. G. (2022). Effects of heat treatment on the corrosion behavior and mechanical properties of biodegradable Mg alloys. Journal of Magnesium and Alloys. https://doi.org/10.1016/j.jma.2022.04.010
Ramalingam, V. V., Ramasamy, P., Kovukkal, M. D., and Myilsamy, G. (2020). Research and Development in Magnesium Alloys for Industrial and Biomedical Applications: A Review. Metals and Materials International, 26(4), 409–430. https://doi.org/10.1007/s12540-019-00346-8
Chowdary, S., Dumpala, R., and Kondaiah, V. V (2018). Influence of heat treatment on the machinability and corrosion behavior of AZ91 Mg alloy. Journal of Magnesium and Alloys, 6(1), 52–58. https://doi.org/10.1016/j.jma.2017.12.001
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