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.

•We calculated the strain energy and interfacial energy of β″ precipitate.•We compared strain energy and interfacial energy of β′-short and β′-long.•We find strain energy is the reason why only β′-long forms.We use density functional theory calculations to explain why β′-long instead of β′-short forms during age-hardening process in Mg–Gd alloys. We calculate strain energies and interfacial energies of β″, β′-short and β′-long in Mg–Gd alloys and find that (1) results of strain energies and interfacial energies of β″ agree well with other theoretical works (2) habit plane of β′-long predicted by density functional theory calculations is consistent with experimental observation (3) strain energy is mainly responsible for the formation of β′-long instead of β′-short in the age-hardening process.

•The slope of Nd content dependence of thermal diffusivity for T4 alloys exhibits a change.•The slope of Nd content dependence of hardness for T4 alloys also exhibits a change.•The changes all occur around the maximum solid solubility 0.68 at.% (3.87 wt%).•Influence of solution atom and second phase on thermal diffusivity were calculated.Thermal conductivities of MgNd alloys in as-cast, T4 and T6 conditions with Nd content varying from 0 to 12 wt% were studied at room temperature, and corresponding microstructures observation and hardness tests were performed. The as-cast MgNd alloys consist of α-Mg and Mg12Nd phases, while Mg12Nd dissolves into α-Mg matrix or transforms to Mg41Nd5 after T4 treatment. T6 treated MgNd alloys are composed of α-Mg and Mg41Nd5 phases. With increasing Nd content, thermal conductivities of MgNd alloys all decrease gradually under as-cast, T4 and T6 conditions. The thermal conductivity of as-cast MgNd alloys is higher than that of T4 counterparts, while lower than that of corresponding T6 alloys. For T4 alloys, the changes in slopes of Nd content dependence of thermal diffusivity and hardness all occur around the saturated point 0.68 at.% (3.87 wt%), which result from no more Nd atoms dissolved into the Mg matrix with increasing Nd content. Quantitative studies about the influence of solution atoms and second phases on thermal diffusivity were made. The thermal diffusivity increment derived from one atom percentage of Nd addition into the Mg matrix is about 67.24 mm2/s while the increment derived from one atom percentage of Nd addition forming second phase is about 11.85 mm2/s.

Rare-earth (RE) element addition can remarkably improve the mechanical properties of magnesium alloys through precipitation hardening. The morphology, distribution and crystal structure of precipitates are regarded as major strengthening mechanisms in the Mg-RE alloys. In order to understand the formation of precipitates during aging at 225 °C in a Mg-10Gd-3Y-0.4Zr alloy (GW103K) with high strength and heat resistance, a high-resolution transmission electron microscopy (HRTEM) was employed to characterize the microstructural evolution. It was found that three types of precipitates were observed in the alloy at the early stage, named as: single layer D019 structure, one single layer D019 structure and one layer of Mg, two parallel single layers (containing RE) and Mg layer in between, which was regarded as ordered segregation of RE, precursors to form β″ and β′ phase, respectively. Both of β″ and β′ phase were transformed from the precursors. It was also found that large size of β′ phase and the small size of β″ phase were constantly existent in the whole aging process. β′ phase played a major role in the strengthening of the GW103K alloys and the decrease of the hardness was caused by the coarsening of β′ phase.HRTEM images taken along <0001> zone axis and corresponding Fourier transform (FT) patterns showing three types of precipitates in the GW103K alloy aged at 225 °C for 0.5 h (a) Single layer D019 structure; (c) One single layer D019 structure and one layer of Mg; (e) Two parallel single layers (containing RE) and Mg layer in between; (b), (d), (f) Corresponding Fourier transform (FT) patterns for (a), (c), (e)

In this paper, the hot compressive deformation characteristics of a Mg–10Gd–3Y–0.5Zr (GW103K) alloy have been investigated by isothermal compression test at the temperature range of 350–450°C and strain rate range of 0.0001–0.1s−1. True stress–strain relationships at various strain rates showed the typical strain hardening and softening stage which is indicative of dynamic recrystallization during deformation. The results showed that the peak stress was obviously dependent on temperature and strain rate. A constitutive equation to describe the deformation process was established based on the hyperbolic sine function. The stress exponent n and apparent activation energy Q were determined to be 3.018 and 203.947 kJ/mol, respectively. Microstructure investigation showed that dislocation slipping was the dominant deformation mechanism during the hot deformation at all conditions. However, at the temperatures lower than 400 °C and strain rates higher than 0.01s−1, twinning was observed to be activated, which indicated another deformation mechanism. Dynamic recrystallization and dynamic precipitation were found to occur simultaneously under such deformation condition.

A high-strength Mg-15.3Gd-1.8Ag-0.3Zr (GQ152K, mass fraction) alloy was prepared by conventional ingot metallurgy process. The solution and aging (denoted as T6) treated alloy exhibits remarkable mechanical properties with ultimate tensile strength of 421MPa and tensile yield strength of 309MPa. It has higher igniting temperature of 1 208 K. Moreover, it can stand against flame at 1 203K for over 6min in vertical burning tests, and its flammability behavior is very similar to that of 6101Al alloy. Vertical burning tests appear to be able to directly study the flammability behavior of Mg alloys and it appears to be a good approach to study the flammability behavior of Mg alloys in an aircraft fire accident.