Recently, the research team led by Prof. Weizhong Han, uncovered that small-volume aluminum alloys with native oxide shell deliver unprecedented strength and toughness, which was published in Acta Materialia 126 (2017) 202-209.
Mechanical properties of small-volume metals have attracted tremendous interests in the past decade due to potential microscale and nanoscale applications. However, some unfavorable deformation characters, such as strain bursts, lack of strain hardening and near-zero uniform elongation, are often displayed by the small-volume metals. These deformation characters plague small-volume metals. How to overcome the deformation instability, lack of strain hardening and strength-ductility tradeoff still remains as a bottleneck for the utilization of microscale and nanoscale metals.

Using Al-4Cu alloy as an example, here we show that a submicron-sized metallic material with ultrathin native oxide shell exhibits a high degree of deformation controllability, unprecedented strain hardening, size strengthening and toughness, in uniaxial tensile deformation. The metal/native oxide “composite” is easy to make, and the emergent properties extend well beyond the benchmark range known for metals in a normalized (i.e., dimensionless) strength-toughness plot (see above). The origin of the combination of strengthening and plastic stability is that an intact ultrathin native oxide shell exerts a strong confinement on dislocation movement and annihilation, thereby breaking the envelope on dislocation storage and strain hardening achievable in small-volume metals. 

Link: http://www.sciencedirect.com/science/article/pii/S1359645416309910