Researchers create high-performance aluminum matrix composites with asymmetric cryocooling

Advancing our journey into outer space requires significant technological breakthroughs, particularly in the field of materials science. In the aerospace industry, the challenge lies in developing materials that are both lightweight and mechanically strong. Metal matrix composites have evolved tremendously since their inception in the twentieth century, and many experts believe they hold the key to future space applications.

Among the most promising metal matrix composites are aluminum matrix composites (AMCs) reinforced with high-entropy alloy particles (HEA_ps). These composites offer superior mechanical properties, including high strength, durability, and plasticity. However, the presence of HEA_ps can also lead to structural defects such as microcracks and microvoids, posing challenges for their practical use.

To address this issue, Professor Hai-liang Yu and his research team from Central South University, China, are exploring a novel method for manufacturing high-performance HEA_p/AMC flat sheets.

In their latest study published in the “Transactions of Nonferrous Metals Society of China,” the team investigated a promising technique called asymmetric cryorolling (ACR), which combines the advantages of cryorolling and asymmetric rolling (AR).

AR is a well-established technique used in steel manufacturing, wherein a metal plate is passed through a rolling mill. This process applies a large shear strain uniformly through the plate’s thickness, thereby reducing the number of defects. The main difference between AR and ACR lies in their operating temperatures. AR is conducted at room temperature, while ACR is performed at cryogenic temperatures achieved using liquid nitrogen.

Previous studies have shown that ACR can enhance the mechanical properties of HEA_p/AMC sheets. However, the specific strengthening mechanism and the relationship between mechanical properties and microstructure during ACR remain unclear. To address this knowledge gap, the researchers prepared HEA_p/AMC sheets using both AR at 298 K and ACR at 77 K. They analyzed the sheets using scanning and transmission electron microscopy techniques, as well as conducted tensile and hardness tests.

Comparing the sheets produced via AR and ACR, the researchers observed significant microstructural differences. The cryogenic processing resulted in sheets with fewer microvoids, finer grain size, and a higher density of dislocations. Moreover, the mechanical tests showed that ACR sheets exhibited significantly higher ductility and strength compared to AR sheets. Prof. Yu highlights, “The ultimate tensile strength of 3 wt% HEA_p/AMCs prepared via ACR reached 253 MPa, 13.5% higher than that achieved by sheets prepared via AR.”

The researchers concluded that the observed differences between ACR and AR were primarily attributed to the volume shrinkage effect of HEA_p/AMCs.
Prof. Yu explains, “The larger the volume shrinkage effect of the aluminum alloy, the more tightly the aluminum will wrap around the reinforcing HEA_ps. This strengthens the bonding between the matrix and the particles. Since the volume shrinkage effect is larger in cryogenic environments, ACR plays a significant role in preventing defects caused by the large plastic deformation of HEA_p/AMC sheets.”

Overall, these findings suggest that ACR could play a pivotal role in the development of new alloys for the aerospace and automotive industries. It may even become the go-to technology for high-performance materials in the future.

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