The microstructures, mechanical properties, and corrosion resistance of ZM21 magnesium alloys with a wide range of calcium (Ca) addition (0.1–1.6 wt%) were investigated. Results showed that the mechanical properties and corrosion resistance were improved with Ca addition because of grain refinement and formation of Ca2Mg6Zn3. However, these properties were deteriorated when Ca contents reached 1.6 wt%. The optimal Ca content of alloys was 0.7 wt%; alloy with this Ca content showed good mechanical performance and corrosion resistance, having a strength of 260 MPa, an elongation of 21.5%, and an average weight loss of 0.77 mg/(cm2 days).

•The influence on thermal conductivity (TC) was drawn as: Ce < Nd < Y < Gd.•TC of both as-cast and as-solutionized Mg–RE alloys decreased with concentration.•Solutionizing treatments decreased TC of Mg–Nd, Mg–Y and Mg–Gd alloys, except for Mg–Ce alloys.•The maximum solid solubility of elements in the α-Mg matrix cannot be neglected.The microstructure and thermal conductivity of four groups of Mg–rare earth (RE) binary alloys (Mg–Ce, Mg–Nd, Mg–Y and Mg–Gd) in as-cast and as-solutionized states were systematically studied. Thermal conductivity was measured on a Netzsch LFA457 using laser flash method at room temperature. Results indicated that for as-cast alloys, the volume fraction of second phases increased with the increase of alloying elements. After solutionizing treatment, a part or most of second phases were dissolved in α-Mg matrix, except for Mg–Ce alloys. The thermal conductivity of as-cast and as-solutionized Mg–RE alloys decreased with the increase of concentrations. The thermal conductivity of as-solutionized Mg–Nd, Mg–Y and Mg–Gd alloys was lower than that of as-cast alloys. Thermal conductivity of as-solutionized Mg–Ce alloys was higher than that of as-cast alloys, because of the elimination of lattice defects and fine dispersed particles during solutionizing treatment. Different RE elements have different influences on the thermal conductivity of Mg alloys in the following order: Ce < Nd < Y < Gd. Ce has the minimum effect on thermal conductivity of Mg alloys, because of the very low solubility of Ce in the α-Mg matrix. The variations in the atomic radius of the solute elements with Mg atom (Δr), valence, configuration of extra-nuclear electron of the solute atoms, and the maximum solid solubility of elements in the α-Mg matrix were suggested to be the main reasons for the differences in thermal conductivity of resulting Mg–RE alloys.Download high-res image (72KB)Download full-size image

•We developed a magnesium alloy with high thermal conductivity of 139.7 W/(m·K).•Thermal conductivity of as–extruded Mg–0.5Mn–0.3Ce alloy was higher than that of other as–extruded alloys.•The weaken texture improves the thermal conductivity and ductility of alloys.•The as–extruded Mg–0.5Mn–0.3Ce exhibits best comprehensive properties.The effect of Ce addition on the microstructure, thermal conductivity and mechanical properties of Mg–0.5Mn alloy was investigated systematically in this study. In addition, the thermal conductivity was measured using flash method in the temperature range of 293–523 K. Results indicate that Ce addition refined the grain structure of both as–cast and as–extruded of Mg–0.5Mn alloys. Moreover, the weakening of texture can be observed by Ce addition. The thermal conductivity of as–cast Mg–0.5Mn–xCe alloys decreased gradually with the increase of Ce content. Meanwhile, the thermal conductivity of as–extruded Mg–0.5Mn–0.3Ce alloy (139.7 W/(m·K)) was higher than that of other as-extruded alloys. Furthermore, the as–extruded Mg–0.5Mn–xCe alloys exhibited higher thermal conductivity than that of as–cast counterparts, except for Mg–0.5Mn–0.6Ce alloy. The weakening of basal texture resulted in the improvement of thermal conductivity of wrought products. The yield strength (YS) and ultimate tensile strength (UTS) of as–extruded Mg–0.5Mn alloys were enhanced by Ce addition. The as–extruded Mg–0.5Mn–0.3Ce alloy showed the best strength and moderate elongation (EL). The UTS, YS and EL of this alloy were 295.9 MPa, 320.9 MPa and 9.6%, respectively.

•The strain compensated constitutive model and DRX kinetics were incorporated into FEM.•The FEM results were in good agreement with the experimental results.•The CA method coupled with FEM results was used to modeling microstructure evolution.•The mean re-grain size first increased and then decreased with the increasing strain.Hot compression tests were conducted on homogenized 5052 aluminum and AZ31 magnesium alloys to establish a strain compensated Arrhenius constitutive model in the temperature range of 573–723 K and 523–673 K with strain rates of 0.001, 0.01, 0.1 and 1 s−1 by using a Gleeble-1500D thermo-simulator. The presented constitutive model, as well as the dynamic recrystallization (DRX) kinetics of both studied alloys, was incorporated into ABAQUS User Subroutine UHARD to provide an effective means to study hot deformation. The simulated results were subsequently referred to the cellular automaton (CA) method to simulate the microstructural evolution of the 5052 and AZ31 alloys. Results show that the constitutive model considering strain compensation offers a high accuracy. In terms of force and volume fraction of DRX, the results of the Finite Element Method (FEM) are in good agreement with the experimental results. The microstructural evolution of both homogenized 5052 and AZ31 alloys during hot compression was simulated using CA coupled the FEM results. Owing to the close connection between dislocation density and flow stress, the alloys present similar characteristics with prolonged simulation time. The mean grain sizes of both studied alloys decrease with increasing strain, revealing that a large deformation degree leads to refined grains. The mean re-grain size initially peaks and then decreases smoothly with increasing strain because of the coupled effect the nucleation and growth of re-grains.

The hot deformation behavior of the homogenized Al–3.2Mg–0.4Er aluminum alloy was investigated at 573–723 K under strain rates of 0.001–1 s−1. On the basis of compression experimental results, an accurate phenomenological constitutive equation that coupled the effects of strain rate, deformation temperature and strain was modeled. Furthermore, a kinetic model of dynamic recrystallization and processing map were also presented. The results show that the flow stress of the studied Al–3.2Mg–0.4Er alloy can be predicted accurately using the proposed constitutive model. The evolution of microstructure and the volume fraction of dynamic recrystallization can be described exactly in terms of S-curves with the proposed kinetic model. Moreover, the processing maps for hot working at different strains were constructed, suggesting the optimum processing conditions for this alloy are 573 K, 0.001 s−1 and 723 K, 0.001–0.1 s−1.

•Thermal conductivity (TC) of as-cast and as-extruded ZM21-xCe alloys was discussed.•TC of as-cast ZM21-0.2Ce alloy was higher than that of ZM21 and ZM21-0.6Ce alloys.•TC of as-extruded alloys increased unconventionally with the Ce content increasing.•TC of as-extruded ZM21-0.6Ce alloy at room temperature was up to 133.29 W/(m·K).•TC of as-extruded ZM21-xCe alloys was higher than their as-cast counterparts.The concentration dependence of thermal conductivity of as-cast and as-extruded Mg–2 wt.%Zn–1 wt.%Mn–[x] wt.%Ce (x = 0, 0.2 and 0.6) alloys was investigated using flash method at room temperature, respectively. According to the present experimental results, the thermal conductivity of as-cast ZM21-0.2Ce alloy was higher than that of as-cast ZM21 and ZM21-0.6Ce alloys, while thermal conductivity of as-extruded alloys increased unconventionally with the Ce content increasing. The obtained highest thermal conductivity of as-extruded ZM21-0.6Ce alloy at room temperature was 133.29 W/(m·K). Meanwhile, as-extruded ZM21-xCe alloys exhibited higher thermal conductivity than their as-cast counterparts because of the precipitation of Mn particles and some intermetallic compounds containing Ce. Furthermore, the texture had an important effect on the thermal conductivity of as-extruded ZM21-xCe alloys.

The effects of the rare earth element Y addition on mechanical properties and energy absorption of a low Zn content Mg–Zn–Zr system alloy and the deformation temperature of optimized alloy were investigated by room tensile test, optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The results show that, after homogenization at 420 °C for 12 h for the as-cast alloys, MgZn phase forms, which decreases the strength of Mg–2.0Zn–0.3Zr alloy with Y content of 0.9 wt%. The tensile strength and elongation of the alloy with a Y addition of 5.8 wt% reach the max value (281 ± 2) MPa and (30.1 ± 0.7) %, respectively; the strength and elongation of Mg–2.0Zn–0.3Zr–0.9Y alloy at the optimized extrusion temperature of 330 °C reach (321 ± 1) MPa and (21.9 ± 0.7) %, respectively. The energy absorption increases with the increase of Y content, the max value reached 0.79 MJ·m−3 with Y content of 5.8 wt%, and the energy absorption of Mg–2.0Zn–0.3Zr–0.9Y alloy at the optimized extrusion temperature of 330 °C reaches 0.75 MJ·m−3.

•The dynamic recrystallization behavior and hot workability of the Mg–2.0Zn–0.3Zr–0.9Y Mg alloy are studied.•The safe and instable deformation domains for the hot working process with different grain size are obtained.•The effect of strain rate and deformation temperature on mechanism of DRX is discussed.•The optimum hot-working parameters with completed DRX grain size are determined.The hot deformation behavior, dynamic recrystallization (DRX) evolution and hot workability of Mg–2.0Zn–0.3Zr–0.9Y alloy were studied by compression test. Compression experiments were performed in temperature range of 250–400 °C and strain rate range of 0.001–1 s−1 using Gleeble 1500D thermo-mechanical simulator. Based on the regression analysis for Arrhenius type equation of flow behavior, the apparent average activation energy of deformation was determined as Q = 236.2 KJ/mol. The DRX kinetic model of Mg–2.0Zn–0.3Zr–0.9Y alloy was established as XDRX=1-exp-1.30(ε-εcε∗)1.51. The DRX kinetic model is sensitive to the DRX mechanism changes caused by deformation conditions. The DRX kinetic model and instability zones were validated by means of microstructure observation.

The effects of stacking sequence changes of the close-packed plane in a long period stacking ordered (LPSO) phase on the hot deformation behavior, dynamic recrystallization (DRX) evolution and hot workability of Mg–2.0Zn–0.3Zr–5.8Y alloy were investigated by compression test. A 14H LPSO phase crystal was fabricated by annealing a solidified crystal with a 18R LPSO structure at 500 °C for 20 h. Compression experiments were performed in temperature range of 300–500 °C and strain rate range of 0.001–1 s−1 using Gleeble 1500D thermo-mechanical simulator.Based on the regression analysis for the Arrhenius type equation of flow behavior, the apparent average activation energy of deformation was determined as Q=348.4 KJ/mol. The kinetics of DRX evolution is calculated as XDRX=1−exp[−2.1542((ε−εc)/ε⁎)1.5119]XDRX=1−exp[−2.1542((ε−εc)/ε⁎)1.5119]. The DRX mechanism of the 14H LPSO phase is almost similar to that of the 18R LPSO phase. On comparison of the alloy with 18R LPSO phase, the formation of lamellar 14H LPSO phase in the Mg matrix can delay the DRX and hinder the growth of DRX grains significantly at the same deformation condition. The transformation of 18R LPSO phase to 14H LPSO phase reduced the workability of Mg–2.0Zn–0.3Zr–5.8Y at low deformation temperatures. The processing map exhibits a deformation domain of complete DRX occurring in the temperature range 454–500 °C and strain rate range of 0.001–0.01 s−1, which are the optimum processing parameters.

The microstructures and mechanical properties of Mg–2.0Zn–1.0Mn (ZM21) alloys with certain amount of Ce and Nd additions were investigated, and the influence mechanism of Ce and Nd on the microstructures and mechanical properties of extruded alloys was discussed. The results indicated that the addition of Nd and Ce can refine the grains in ZM21 alloy, for which the distribution density of second phase particle played a major role to hinder the growth of dynamic recrystallization (DRX) grain in alloys by adding a content of 0.4 wt.% Ce and Nd. The average grain size of ZM21 alloy with the additions of 0.4 wt.% Nd and Ce reached 6 ± 3 μm and 13 ± 2 μm, respectively. Adding Ce and Nd to ZM21 alloy, the changes of mechanical properties were mainly attributed to a reduction in basal texture intensity, refinement grain size as well as the dispersion density and distribution position of fine second phase particles. Furthermore, by addition of Ce and Nd to ZM21 alloy, the non-basal plane slip system could be activated which decreased the basal texture intensity.