As a brand-new type of multi-principal component solid solution alloy, high-entropy alloys (HEAs) have drawn widely attention of researchers due to their unique alloy design concept and amazing performances, which has become a hot spot in current material research. Among them, light-weight high-entropy alloys (LWHEAs) are thought to be a novel kind of light-weight alloy materials developed based on the light-weight design of HEAs. They feature high specific strength and excellent specific hardness in general, which is superior to most traditional lightweight alloys, implicating great application potential in the fields of aerospace, energy transportation and electronic communication. However, the current research of LWHEAs is still at an exploratory stage, and two stern challenges encountered in developing LWHEAs: (i)in terms of the alloy design, most LWHEAs are developed by a trial-and-error method based on the empirical criteria of traditional HEAs consist of transition metal elements, and reliable methods for guiding the design of LWHEAs are not available; (ii) in terms of the preparation technology, it is difficult to produce bulk LWHEA materials with simple microstructures and exceptional properties by using the current preparation methods. Hitherto, almost 100 kinds of LWHEAs have been explored experimentally by researchers. And they have been striving to search for suitable empirical criteria for predicting the phase structure of LWHEAs, which involving many thermos-physical parameters such as the mixing entropy (ΔSmix), the mixing enthalpy(ΔHmix), the atom radius difference(δ), and the valence electron concentration(VEC).More recently, the use of computer simulation methods to assist LWHEA design begins to develop gradually and shows apparent advantages, for instance, utilizing phase diagram calculation (CALPHAD) and first-principles calculation (DFT) to predict the phase formation and phase transition of LWHEAs. Although the vacuum casting provides a simple route to obtain bulk LWHEAs, many LWHEAs prepared from which display a multi-phased microstructure. Works in the past years have established a new avenue to overcome the complex microstructures, by introducing mechanical alloying process, which have successfully achieved the reduced tendency of alloys to form complex phases such as intermetallic compounds (IM), and produced LWHEAs with simpler phase constitutions. Besides, although most as-cast LWHEAs generally manifest complex multi-phased microstructure with poor plasticity, the Al-rich (or Mg-rich) LWHEAs, according to the existing data, form simple microstructures very often with a dominated solid solution (SS) phase and traces of IM phase, and in consequence show the potential for a good combination of strength and ductility. In this review, according to the current research status in LWHEAs, the light elements selection rule is first summarized. Also, the recent deve-lopment of LWHEAs including alloy design methods, preparation processes, microstructures and properties are summed up. In addition, the empirical phase formation rules about LWHEAs design also are analyzed in details, especially, the phase formation rules suitable to Ⅰ-type and Ⅱ-type LWHEAs respectively are proposed, which is supposed to guide future LWHEAs design. Finally, the main problems of LWHEAs are discussed and future research directions in LWHEAs are suggested. © 2020, Materials Review Magazine. All right reserved.
