In brief

SEM micrographs of magnesium alloys subjected to conventional (left) and microwave sintering (right). While the magnesium particles retained their spherical shape in conventionally sintering, microwave sintering produced specimens with altered shapes in a shorter period of time.

© Mojtaba Salehi

Magnesium alloy manufacturing goes green

6 Oct 2021

Scientists have developed a faster, more energy-efficient method for 3D printing magnesium alloys, creating new opportunities for biomedical applications.

Popularly known as an important mineral for maintaining bone health, magnesium is also an attractive material for manufacturing everything from airplane parts to bone implants, thanks to its lightweight and biodegradable properties. However, the element is also highly reactive, making it difficult to fabricate related compounds using advanced technologies like additive manufacturing (AM) or 3D printing.

These challenges have led researchers to look for novel ways of applying AM protocols in the manufacturing of complex and customizable magnesium alloys. One such method is binder jet AM, which shapes powdered metals into their near-final form. Unlike fusion-based AM methods, binder jetting can be done at almost ambient temperatures. The downside, however, is that binder jetting is more time-consuming, hindering its widespread industrial adoption.

In their latest study, Mojtaba Salehi, Sharon Nai and colleagues at A*STAR’s Singapore Institute of Manufacturing Technology (SIMTech) explored alternative AM methods that are more efficient. Specifically, the team sought to shorten a lengthy post-processing step called sintering, where powdered particles are fused into a solid material through heat or pressure.

Conventional sintering involves an external source generating heat that is transferred to the material, while in another technique called microwave sintering, the material absorbs microwave energy that is then converted into heat. The team’s primary aim was to investigate if and how microwave heating shortened the sintering time of 3D printed magnesium parts, as compared to conventional sintering.

To this end, the researchers used the 3D printing method they established to manufacture magnesium alloys and then tested various sintering durations in both a conventional and a microwave furnace.

Comparing the physical, chemical, and mechanical properties of the end products, the researchers found that microwave-sintered objects could be produced three times faster than their conventionally-sintered counterparts, resulting in a nine-fold energy saving.

“Our comparative analyses of the properties and sintering mechanisms in the microwave and conventional furnaces revealed that the synergy between the post-print microwave heating and the binder-free method that we previously established to eliminate the lengthy binder removal step, could lend itself to be the fastest and greenest approach for binder jet AM,” Salehi said.

The researchers also explored the potential of using printed magnesium specimens as bone scaffolding. Intriguingly, magnesium parts sintered for 15 hours in a microwave furnace were found to have comparable interconnected pore structure and physical properties to the human cortical bone.

The team is now collaborating with research and industry partners in Singapore and Germany to develop digital manufacturing solutions for fabricating biodegradable magnesium implants. “Such an end-to-end manufacturing solution enables the fabrication of customized porous magnesium parts to revolutionize the future of magnesium alloys for implant applications,” Salehi said.

The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology (SIMTech).

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Salehi, M., Seet, H.L., Gupta, M., Farnoush, H., Maleksaeedi, S., et al. Rapid densification of additive manufactured magnesium alloys via microwave sintering. Additive Manufacturing 37, 101655 (2021) | article

Salehi, M., Maleksaeedi, S., Nai, S.M.L., Meenashisundaram, G.K., Goh, M H., et al. A paradigm shift towards compositionally zero-sum binderless 3D printing of magnesium alloys via capillary-mediated bridging. Acta Materialia 165, 294-306 (2019) | article

About the Researchers

Mojtaba Salehi obtained his PhD in Mechanical Engineering from the National University of Singapore with a focus on additive manufacturing. He joined the Additive Manufacturing Group at A*STAR’s Singapore Institute of Manufacturing Technology (SIMTech) as a Scientist in 2019. He has over ten years of experience in advanced manufacturing of materials, and has published more than ten journal articles and one book.
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Sharon Nai

Senior Principal Scientist and R&D Director

Singapore Institute of Manufacturing Technology (SIMTech)
Sharon Nai is a Senior Principal Scientist and R&D Director at Singapore Institute of Manufacturing Technology (SIMTech). She obtained her PhD in Mechanical Engineering from the National University of Singapore. Her research interests include the development of metallic powders (e.g. Al alloys, Ti alloys, Inconel alloy, steels, high entropy alloys, composites) for additive manufacturing and additive manufacturing process and system development to realise the end-to-end processing of complex geometrical multi-material parts with multi-functionalities. She has also published two books, two book chapters and over 130 journal papers.

This article was made for A*STAR Research by Wildtype Media Group