Mg-4.0Zn alloy composite reinforced by NiO-coated CNTs (NiO@CNTs) was synthesized by combining ball-milling and a casting process. The yield strength (YS) and elongation to failure of the composite were dramatically increased by 44.9% and 38.6%, respectively, compared to its alloy counterpart. The significantly enhanced mechanical properties of the as-synthesized composite are mainly ascribed to an improved interfacial bond, grain refinement and good dispersion of CNTs in the matrix via. coating NiO on CNTs. It is shown that the NiO-nanolayer on the CNTs significantly enhances the interfacial bonding strength and effectively prevents the agglomeration of CNTs. NiO@CNTs are, therefore, expected to be a highly sustainable and dispersible reinforcement for magnesium matrix composites with superior performance.

•The surface nanocrystals with random orientation were obtained by SMAT.•The hardness of Mg alloy could be increased largely from 98 HV to 146 HV by SMAT.•The aging precipitation could be promoted by the SMAT-induced dislocation.Precipitation hardening plays a significant role in improving the strength of Mg-RE (RE = rare earth) alloy due to the formation of precipitates. It is vital to control the precipitation behavior in order to optimize the mechanical properties of Mg-RE alloy. The present study explored one new way to promote the precipitation behavior of GW103K alloy by surface mechanical attrition treatment (SMAT). As compared with the conventional heat treatment, more precipitates could be formed under a shorter aging duration after SMAT, which results in finer grain size and higher micro hardness than the as-extruded one. The promotion of precipitation behavior is attributed to the high dislocation density induced by SMAT, which leads to a low nucleation energy and a high nucleation rate for the formation of precipitate.

In present work, the deformation behavior of AZ31 Mg alloy with surface mechanical attrition treatment (SMAT) had been studied. The microstructure and mechanical properties of AZ31 Mg alloy with SMAT were investigated. The results indicated that a gradient nanostructure could be formed in sample by SMAT, in which the grain size increased gradually from surface to matrix. A depth-dependent gradient microhardness was also formed due to the corresponding gradient microstructure. Yield strength and ultimate tensile strength of AZ31 Mg alloy with SMAT were significantly improved combining with decrease of fracture elongation. The effect of SMAT on anisotropy of mechanical properties of AZ31 alloy had been discussed and analyzed. The plastic anisotropy of the sample increased significantly after SMAT, which was related to the texture variation of rolled sheet and special deformation behavior of gradient nanostructure. Finally, in order to illuminate the difference in deformation behavior between fine and coarse grained microstructure, the in-situ tensile deformation behavior of AZ31 Mg alloy with one-side gradient structure had been studied by SEM. The deformation mechanism of AZ31 Mg alloy with gradient structure had been put forward.

AZ91D alloy composites with 1.0% CNTs have been fabricated by a method combined ball milling with stirring casting. The composite was investigated using optical microscopy(OM), X-ray diffraction(XRD), Fourier transform infrared spectroscope (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM) and room temperature (RT) tensile test. The results show that CNTs were homogeneously distributed in the matrix and maintained integrated structure. The yield strength and ductility of AZ91D/CNTs composite were improved by 47.2% and 112.2%, respectively, when compared with the AZ91 alloy. The uniform distribution of CNTs and the strong interfacial bonds between CNT and the matrix are dominated to the simultaneous improvement of yield strength and ductility of the composite. In addition, the grain refinement as well as the finer β phase (Mg17Al12) with homogenous distribution in the matrix can also slightly assist to the enhancement of the mechanical properties of the composite.

Carbon nanotubes (CNTs) are novel reinforcement of Mg-based composites because of their attractive mechanical properties. However, in general, nanosize CNTs did not completely impart their exceptional properties to the Mg matrix because of the poor interfacial bonding between CNTs and the matrix and the aggregation of CNTs, which largely limit their applications in Mg-based composites. In this study, a novel method was developed to increase the interfacial bonding strength by coating magnesium oxide (MgO) nanoparticles on the surface of CNTs. The detailed crystallographic analysis by transmission electron microscopy (TEM) confirmed that two types of bonds were formed at the CNTs/MgO interface: nanoscale-contact bonds and diffused interfacial bonds. Moreover, for the first time, the orientation relationships of (11¯1)MgO//(011¯1)α−Mg and [011]MgO//[21¯1¯0]α−Mg with the semicoherent interface characteristics were observed between MgO and the matrix of α-Mg. The interatomic spacing misfit at the MgO/α-Mg interface is 6.5%, which indicates a good lattice space matching between MgO and the matrix of α-Mg. The yield strength and elongation of AZ91-3.0MgO@CNT composite were enhanced by 69.0% and 22.9%, respectively, when compared with the AZ91 alloy. The mechanism of strengthening of AZ91 alloy composites reinforced by MgO@CNTs was discussed in detail.

Mg2Sn (100) surfaces were investigated using ab-initio method based on density functional theory in order to explore the surface properties. It is found that both the eleven-layers for Mg-termination surfaces and the nine-layers for Sn-termination surfaces are all converged very well. The effects of relaxation mainly occurred within the three outermost atomic layers for both Mg and Sn terminations during the surface relaxation. Mg-termination surfaces are more stable than Sn-termination surfaces according to the analysis of surface energy. The density of states reveals the metallic property of both Mg-termination and Sn-termination surfaces. Covalent bonding exists in Mg2Sn (100) surfaces according to the analysis of partial density of states.

•C14-type AMg2 (A = Ca, Sr and Ba) have been studied from first-principles method.•Mechanical anisotropies are well described and discussed.•All of them are stable energetically, mechanically and dynamically.•The BaMg2 has a high degree of angular bonding characters.Using first principles total energy calculations within the generalized gradient approximation (GGA), we have investigated the mechanical and thermodynamics properties of C14-type Laves phases AMg2 (A = Ca, Sr and Ba). Our results of equilibrium lattice parameters and formation enthalpy agree closely with previous experimental results. In particular we have discussed the thermodynamic stabilities and mechanical anisotropies of these phase structures. The polycrystalline elastic moduli have been deduced by Voigt–Reuss–Hill arithmetic approximation. Subsequently, the ductility and brittleness are characterized with the estimation from Pugh’s rule (B/G) and Poisson’s ratio. Additionally, the Debye temperature is calculated from the average elastic wave velocity obtained from bulk and shear moduli. The calculations of density of states and charge density difference are performed to reveal the underlying mechanism of electronic structure. Finally, variations of thermodynamic properties with temperature are predicted by calculating phonon frequencies combined within the quasi-harmonic approximation.

•Sr–Zn binary compounds are investigated from first-principles calculations.•All intermediate compounds are energetically and mechanically stable.•Mechanical properties are well described and discussed.•SrZn2 is found to be highly anisotropic in its elastic property.We have studied the structural, anisotropic elastic and electronic properties of Sr–Zn binary intermetallic compounds using first-principles plane-wave pseudo-potential method. Our calculated equilibrium lattice parameters are validated by comparison with available experimental data. Results of formation enthalpy have indicated that each intermediate compound is energetically stable, and they are all mechanically stable according to the criteria of elastic stability. For the first time, the calculated elastic constants have allowed us to characterize the elastic anisotropy of acoustic velocity. Additionally, mechanical parameters, such as bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio σ are deduced by means of Voigt–Reuss–Hill method. It is discovered that, with increasing concentration of Zn, the mechanical moduli and theoretical Vickers hardness of Sr–Zn compounds could be improved. Mechanical anisotropies are discussed by calculating different anisotropic indexes and factors. Finally, calculations on density of states and atomic charge populations are performed to reveal the underlying mechanisms of electronic structure.

The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y (wt%) alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing (SDAS) of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates (Rc) from 10.2 to 23 K/s, which can be predicted using a empirical model of \( {\text{SDAS}} = 68R_{\text{c}}^{ - 0.45} \) and \( {\text{SDAS}} = 73R_{\text{c}}^{ - 0.45} \), respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction (Vf) of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory.

A nanocrystalline layer (NL) was fabricated on the surface of AZ31 magnesium (Mg) alloy sheet by surface mechanical attrition treatment (SMAT). The microstructure of the Mg alloy was characterized by optical microscopy, X-ray diffraction and microhardness test. The results showed that both the microstructure and microhardness of AZ31 Mg alloy sheet after SMAT revealed a gradient distribution along depth from surface to center. The thermal stability of the NL was investigated through characterizing the microstructure evolution during the post-isothermal annealing treatment within the temperature range from 150 to 250 °C. The NL exhibits a certain degree of thermal stability below 150 °C, while it disappears quickly when annealing at the temperature range of 200–250 °C. The grain growth kinetics of the nanocrystalline of AZ31 Mg alloy induced by SMAT was investigated. The activation energy of nanocrystalline AZ31 Mg alloy was obtained with a value of 92.8 kJ/mol.

•Structural properties and electronic structure of Al2Zr and Al2Hf are studied.•Mechanical properties are well described and discussed.•The Debye temperature and anisotropic sound velocity are first assessed.•The bonding strength for Al–Zr bonding is stronger than that of Al–Hf bonding.Structural, mechanical and electronic properties of Laves phases Al2Zr and Al2Hf with C14-type structure were investigated by performing the first-principle calculations. The calculated equilibrium structural parameters agree closely with available experimental values. Mechanical parameters, such as bulk modulus B, shear modulus G, Young’s modulus E and the Poisson’s ratio ν are determined within the framework of the Voigt–Reuss–Hill approximation. We show that both Al2Zr and Al2Hf are mechanically stable and brittle with the estimation from the Poisson’s ratio and the B/G relationship. The mechanical anisotropies of the two phases are discussed in detail using several different anisotropic indexes and factors, showing that the anisotropy degree of Al2Hf is slightly larger than that of Al2Zr. In addition, the Debye temperature and anisotropic sound velocity of the two phases are predicted. Finally, the electronic structures are determined to reveal the bonding characteristics of both phases. These results are helpful to deepen the understanding of the physical and chemical nature of C14-type Al2Zr and Al2Hf.

The effect of cryogenic treatment on the microstructure and mechanical properties of Mg–1.5Zn–0.15Gd (at%) alloy were investigated. The result showed that numerous W phase particles precipitated from the Mg matrix after cryogenic treatment. With increasing cryogenic treatment duration from 1 min to 24 h, the volume fraction of W phase precipitate also increased, which agreed with the Kolmogorov–Johnson-Mehl–Avrami model. The kinetics of such precipitates was attributed to the additional space coming from the lattice contraction of Mg under cryogenic environment. After cryogenic treatment for 24 h, the ductility of alloy was enhanced by 79%, since the homogenous distributed W phase with nanoscale activated the nucleation of twins during deformation. One formation criterion of precipitation in Mg alloy under cryogenic environment was suggested. Cryogenic treatment could be efficient only for the formation of precipitate with a much lower atom density than the matrix.

First-principles computation methods play an important role in developing and designing new magnesium alloys. In this article, we present an overview of the first-principles modeling techniques used in recent years to simulate ideal models of the structure of strengthening compounds in Mg alloys. For typical Mg compounds, structural stability, mechanical properties, electronic structure and thermodynamic properties have been discussed. Specifically, the elastic anisotropies of these compounds are examined, which is highly correlated with the possibility of inducing micro-cracks. Furthermore, some heterogeneous nucleation interfaces investigated by first-principles method are reviewed. Some of the theoretical results are compared with available experimental observations. We hope to illustrate that the first-principles computation can help to accelerate the design of new Mg-based materials and the development of materials genome initiative. Remaining problems and future directions in this research field are considered.

By surface mechanical attrition treatment (SMAT), a gradient nano structure (GNS) from the surface to center was generated in the AZ31 alloy sheet. The tribological behavior of AZ31 alloy with GNS was systematically investigated by using dry sliding tests, a 3D surface profile-meter and a scanning electron microscope equipped with an energy-dispersive spectrometer. The experimental results indicate that the Mg alloy with GNS exhibits better wear resistance comparing to the as-received sample, which is associated to the alteration of wear mechanism at different sliding speeds. The Mg alloy with GNS presents the wear mechanism of the abrasive wear at 0.05 m/s and the oxidative wear at 0.5 m/s, respectively. Moreover, the GNS can effectively promote the reaction between the oxygen and worn surface, which leads to a compact oxidation layer at 0.5 m/s. The effect of oxidation layer on the wear resistance of the Mg alloy was also discussed.