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Here, we show the strategies to strengthen Mg alloys through modifying the matrix by planar faults and optimizing the local lattice strain by solute atoms. The anomalous shifts of the local phonon density of state of stacking faults (SFs) and long periodic stacking-ordered structures (LPSOs) toward the high-frequency mode are revealed by HCP-FCC transformation, resulting in the increase of vibrational entropy and the decrease of free energy to stabilize the SFs and LPSOs. Through integrating bonding charge density and electronic density of states, electronic redistributions are applied to reveal the electronic basis for the ‘strengthening’ of Mg alloys.

High-entropy alloys: cluster-and-glue atoms behind exceptional properties A cluster-and-glue model of atomic arrangements explains the yield strength and mechanical response of high entropy alloys. Inspired by metallic glass, a team led by William Yi Wang at China’s Northwestern Polytechnical University and collaborators in the United States of America used molecular dynamics to build different atomic arrangements of refractory high entropy alloys consisting of four or more elements. Depending on atomic size and the periodic table group of each atom, some atoms organized into clusters while others glued the clusters together. Chemical bonds broke and formed with plastic deformation as the alloys went from one atomic arrangement to another via the glue atoms, causing defect avalanches explaining the serrated mechanical response of high entropy alloys. Taking into account atomic arrangement may thus help us predict the properties of high entropy alloys.

The influence of the initial solidification conditions on the as-cast structures and the following aged structures of centrifugally cast HK40 steel has been investigated. The relationships between the solidification process and the structure characteristics have also been discussed in detail. The results show that without the introduction of an electromagnetic field during the centrifugal solidification, enhancing the cooling ability of the cast mold markedly promotes coarsening and continuous growth of the columnar grains. Under the same cooling conditions, an electromagnetic field applied during solidification not only promotes the development of the equiaxed grains, but also results in a remarkable refinement of both the columnar grains and the equiaxed grains. Either improving the cooling ability of the cast mold or applying an electromagnetic field during the centrifugal solidification, increases the precipitating width of the secondary carbides along the grain and dendrite boundaries, and delays coalescing and coarsening of the secondary carbides in the following aging process. [ABSTRACT FROM AUTHOR]