In the quest to bolster the wear resistance of magnesium alloys, a team of researchers led by Jie Li from the Institute of Advanced Wear & Corrosion Resistant and Functional Materials at Jinan University in Guangzhou, China, has uncovered a counterintuitive finding that could reshape the future of magnesium alloy applications in the energy sector. Their study, published in the *Journal of Magnesium and Alloys* (translated as *Magnesium and Its Alloys*), challenges the conventional wisdom that adding more hard particles to an alloy invariably improves its wear resistance.
Magnesium alloys, known for their lightweight and high strength-to-weight ratio, are increasingly being considered for use in the energy sector, particularly in applications where weight reduction is critical, such as in electric vehicles and renewable energy technologies. However, their wear resistance has often been a limiting factor. The conventional approach to improving wear resistance has been to introduce hard particles, such as precipitates, into the alloy. Yet, as Li and his team discovered, this strategy can backfire under certain conditions.
The researchers investigated the wear behaviors of three AZ-Mg alloys with varying precipitate contents: AZ31 (2.1%), AZ61 (3.8%), and AZ91 (5.0%). They subjected these alloys to axial loads of 3 and 15 N to simulate different wear scenarios. While the wear volume of the alloys decreased with increasing precipitate content at both loads, the relative wear resistances of AZ61 and AZ91 compared to AZ31 decreased as the load increased. Specifically, the wear resistance of AZ61 dropped by 7% and AZ91 by 28% as the load increased from 3 N to 15 N.
“This unexpected decline in wear resistance with higher precipitate content under increased load is a significant finding,” Li explained. “It suggests that the conventional approach of adding more hard particles may not always be the best strategy for enhancing wear resistance in magnesium alloys.”
The team attributed this phenomenon to the inhibition of mechanical twin formation by the precipitates. Mechanical twins are microscopic deformations that occur in the material under stress and are precursors to the formation of a protective tribolayer—a thin layer that forms on the surface of the material during wear and helps to reduce further wear. The precipitates, however, hinder the formation of these twins, thereby weakening the alloy’s wear hardening ability.
Moreover, the researchers found that the inhibitory effect of the precipitates on the tribolayer was amplified by the load. At a lower load of 3 N, the tribolayer hardness increased with precipitate content, but at a higher load of 15 N, the tribolayer hardness decreased with increasing precipitate content. This indicates that the precipitates not only inhibit the formation of mechanical twins but also make the tribolayer more susceptible to higher loads.
The implications of this research are profound for the energy sector, where magnesium alloys are increasingly being considered for lightweight applications. “Our findings suggest that instead of simply adding more hard particles, we should focus on promoting the formation of mechanical twins to enhance the wear resistance of magnesium alloys,” Li said. “This could open up new avenues for the design of wear-resistant magnesium alloys tailored for specific applications in the energy sector.”
The study provides a new concept for the design of wear-resistant magnesium alloys, one that prioritizes the promotion of mechanical twin formation over the mere addition of hard particles. This shift in approach could lead to the development of magnesium alloys with superior wear resistance, making them more suitable for use in demanding applications in the energy sector.
As the world continues to seek lightweight and durable materials for sustainable energy technologies, this research offers a promising path forward. By understanding and leveraging the role of mechanical twins in wear resistance, researchers can pave the way for the next generation of magnesium alloys, driving innovation and progress in the energy sector.