Solute strengthening of prism edge dislocations in Mg alloys

The poor ductility of hcp Mg is attributed to the low activity of non-basal slip systems and so activation of prismatic slip can aid ductility in rolled sheets by providing three additional <a> Burgers vector slip systems. Experimental studies show that dilute additions of alloying elements such as Zn and Al leads to softening of prismatic slip at low temperatures but strengthening at higher temperatures. Here, the role of solute strengthening of prismatic edge dislocations is investigated as a possible explanation for the higher-T strengthening. Mg-Zn is studied using first-principles inputs in a parameter-free solute strengthening theory. First-principles DFT is necessary to accurately assess the strong solute chemical interaction energies in the core of the compact edge dislocation. Such calculations are subtle due to motion of the dislocation in the presence of the solute, and methods to obtain reliable results with acceptable computational cost are discussed. While interaction energies of Zn in the prism edge core can be quite large (+/- 0.34 eV), the edge solute strengthening of prismatic slip in dilute Mg-Zn remains well below experiments at high temperatures. However, the large difference (0.68 eV) in Zn/dislocation interaction energies across the core of the edge dislocation suggests strengthening by dynamic strain aging as an explanation for the higher-T strengthening.

hcp Mg的延展性不佳归因于非基面滑移系统的活性较低，因此通过激活棱柱滑移可以为轧制板材提供三个额外的<a> Burgers矢量滑移系统，从而有助于提高其延展性。实验研究表明，添加少量合金元素如Zn和Al在低温下会导致棱柱滑移软化，而在高温下则强化。在此，本研究旨在探讨溶质强化棱柱位错的作用，以解释高温下的强化现象。Mg-Zn合金的研究采用了基于第一原理的输入，并在参数自由溶质强化理论中进行。为了精确评估紧凑型棱柱位错核心处的强溶质化学相互作用能，需要使用第一原理密度泛函理论（DFT）。由于位错在溶质存在下的运动，此类计算相当复杂，本文讨论了获得可靠结果且计算成本可接受的方法。尽管Zn在棱柱边缘核心的相互作用能可能相当大（±0.34 eV），但稀释的Mg-Zn合金在高温下棱柱滑移的边缘溶质强化仍远低于实验结果。然而，Zn/位错相互作用能在位错核心处存在较大的差异（0.68 eV），这表明动态应变老化是解释高温强化的可能机制。