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One of the major obstacles restricting the wide applications of Mg alloys is their low Young's modulus at ∼45 GPa, which is uncompetitive to Al alloy over 60 GPa. To resolve this issue, we proposed a new strategy of designing ultra-light Mg-Li alloys by employing the microscale compounds in both HCP and BCC grains to achieve high Young's modulus. HCP or BCC alone cannot achieve a high modulus due to the segregation of solutes at the grain boundaries and the formation of brittle intermetallics in the interdendritic region. We designed chemistry that is so perfect to arrest the excess solutes inside the BCC matrix during solidification and engulf pre-solidified rare earth particles by HCP primary grains which have such a lean chemical composition that has almost no segregation. During solution heat treatment, the dissolution of solutes pushes the BCC boundary towards HCP grains by Ostwald ripening (BCC structures are interconnected but the HCP structures are isolated). During low-temperature aging heat treatment, nucleation of HCP structure on the rare earth particles inside the BCC grain is found, degrading the strength. Therefore, a novel Mg-Li-Al-Zn-Y-Mn-Gd (LAZWMV) alloy with a very high modulus was designed which reaches Young's modulus as high as 61.4 GPa. Micro-compounds (AlLi and Al-X) with average equivalent diameters of 3.76 µm and 6.55 µm were quantified in 3D using X-ray computed tomography and nanoindentation tests for establishing the microstructure-modulus correlation. The influence of Li addition on Mg-Mg was calculated by DFT calculations and the mechanism of modulus improvements has been proposed. [Display omitted] • Ultra-light Mg-Li alloy was designed with high strength and high modulus. • Super-high Young's Modulus of 61.4 GPa was first reported for a novel Mg alloy. • Nanoindentation uncovers the principles of modulus increase in Mg-Li alloys. • Quantitative 3D characterization of high modulus phase using XCT prectict alloy properties. • DFT calculation of Mg-Mg bonds explores the effects of heat treatments. [ABSTRACT FROM AUTHOR]

In materials science and engineering, a significant amount of research has been carried out using indentation techniques in order to characterize the mechanical properties and microstructure of a broad range of natural and engineered materials. However, there are many unresearched or partly researched areas, such as, for example, the investigation of the shape of the indentation load–displacement curve, the associated mechanism in porous materials with clastic texture, and the influence of the texture on the constitutive behavior of the materials. In the present study, nanoindentation is employed in the analysis of the mechanical behavior of a benchmark material composed of plaster of Paris, which represents a brand of highly porous-clastic materials with a complex structure; such materials may find many applications in medicine, production industry, and energy sectors. The focus of the study is directed at the examination of the influence of the porous structure on the load–displacement response in loading and unloading phases based on nanoindentation experiments, as well as the variation with repeating the indentation in already indented locations. Events such as pop-in in the loading phase and bowing out and elbowing in the unloading phase of a given nanoindentation test are studied. Modulus, hardness, and the elastic stiffness values were additionally examined. The repeated indentation tests provided validations of various mechanisms in the loading and unloading phases of the indentation tests. The results from this study provide some fundamental insights into the interpretation of the nanoindentation behavior and the viscoelastic nature of porous-clastic materials. Some insights on the influence of indentation spacing to depth ratio were also obtained, providing scope for further studies. [ABSTRACT FROM AUTHOR]