Zhanyi Cao

Pure Single-Crystalline Na1.1V3O7.9 Nanobelts as Superior Cathode Materials for Rechargeable Sodium-Ion Batteries

Pure single‐crystalline Na1.1V3O7.9 nanobelts are successfully synthesized for the first time via a facile yet effective strategy. When used as cathode materials for Na‐ion batteries, the novel nanobelts exhibit excellent electrochemical performance. Given the ease and effectiveness of the synthesis route as well as the very promising electrochemical performance, the results obtained may be extended to other next‐generation cathode materials for Na‐ion batteries.

Microstructures and wear properties of graphite and Al2O3 reinforced AZ91D-Cex composites

Abstract The magnesium matrix composites reinforced by graphite particles and Al 2 O 3 short fibers were fabricated by squeeze-infiltration technique. The additions dispersed uniformly and no agglomeration and casting defect were observed. The microstructures and wear properties of the composites with different Ce contents of 0, 0.4%, 0.8% and 1.0%, respectively, were investigated. Especially, the effect of Ce on the properties was discussed. The results reveal that Ce enriches around the boundaries of graphite particles and forms Al 3 Ce phase with Al. The addition of Ce refines the microstructures of the composites. With the increase of Ce content, the grain size becomes smaller and the wear resistance of the composite is improved. At low load, the composites have similar worn surface. At high load, the composite with 1.0% Ce has the best wear resistance due to the existence of Al 3 Ce phase. The Al 3 Ce phase improves the thermal stability of the matrix so the graphite particles can keep intact, which can still work as lubricant. At low load, the wear mechanism is abrasive wear and oxidation wear. At high load, the wear mechanism changes to delamination wear for all the composites.

Effect of graphite content on wear property of graphite/Al2O3/Mg-9Al-1Zn-0.8Ce composites

Using squeeze-infiltration technique, Mg-9Al-1Zn-0.8Ce composite reinforced by graphite particles and Al2O3 short fibers was fabricated. The reinforcing phases combined closely with the matrix and no agglomeration was observed. The microstructure, hardness and wear property of the composites with the graphite content of 5%, 10%, 15% and 20% were investigated, respectively. The results reveal that Ce tends to enrich around the boundaries of graphite particles and Al2O3 short fibers, and forms Al3Ce phase. When the graphite content increases to 20%, the grain size becomes small. Moreover, with increasing the graphite content, the microhardness of the composites decreases but the wear resistance increases. The graphite which works as lubricant during dry sliding process decreases the wear loss. At low load, the wear mechanism of the composite is mainly abrasive wear and oxidation wear; at high load, except that the composite with 20% graphite is still with abrasive wear and oxidation wear, the wear mechanism of other composites changes to delamination wear.

Effect of Yttrium addition on microstructure and mechanical properties of Mg–Zn–Ca alloy

Abstract The effects of Y on the microstructure and mechanical properties of the solution treated Mg–6Zn–0·5Ca alloys were investigated in this study. The results indicated that the alloy was mainly composed of α-Mg solid solution and the secondary phases of MgZn2, Ca2Mg6Zn3 and Mg12ZnY. The grains size of the solution treated alloys decreased from 210 to 80 μm with the increasing of Y content up to 1·5 wt-%. The great progressional mechanical properties were observed in the prepared Mg–6Zn–0·5Ca–1Y alloy at room temperature, the ultimate tensile strength (σb), tensile yield strength (σ0·2) and elongation (ϵ) were 284 MPa, 166 MPa and 14·7% respectively, which was determined by the combined contributions of solid solution strengthening, precipitation strengthening plus grain size refinement strengthening.

Effects of semi-solid isothermal process parameters on microstructure of Mg-Gd alloy

Abstract The effects of semi-solid isothermal process parameters on the microstructure evolution of Mg-Gd rare earth alloy produced by strain-induced melt activation (SIMA) were investigated. The formation mechanism of the particles in the process of the isothermal treatment was also discussed. The results show that the microstructure of the as-cast alloy consists of α-Mg solid solution, Mg 5 RE and Mg 24 RE 5 (Gd, Y, Nd) phase. After being extruded with an extrusion ratio of 14:1 at 380 °C, the microstructure of Mg-Gd alloy changes from developed dendrites to near-equiaxed grains. The liquid volume fraction of the semisolid slurry gradually increases with elevating isothermal temperature or prolonging isothermal time during the partial remelting. To obtain an ideal semisolid slurry, the optimal process parameters for the Mg-Gd alloy should be 630 ? for isothermal temperature and 30 min for the corresponding time, respectively, where the volume fraction of the liquid phase is 52%.

Microstructure and mechanical properties of Mg-6Al-0.3Mn-xY alloys prepared by casting and hot rolling

Abstract Mg-6Al-0.3Mn-xY (x=0, 0.3, 0.6 and 0.9, mass fraction, %) magnesium alloys were prepared by casting and hot rolling process. The influence of yttrium on microstructure and tensile mechanical properties of the AM60 magnesium alloy was investigated. The results reveal that with increasing the yttrium content, Al2Y precipitates form and the grain size is reduced. The ultimate strength, yield strength and elongation at room temperature are 192 MPa, 62 MPa and 12.6%, respectively, for the as-cast Mg-6Al-0.3Mn-0.9Y alloy. All these properties are improved obviously by hot rolling, and the values are up to 303 MPa, 255 MPa and 17.1%, respectively, for the rolled Mg-6Al-0.3Mn-0.9Y alloy. The improvement of mechanical properties is attributed to continuous dynamic recrystallization and the existence of highly thermal stable Al2Y precipitate which impedes the movement of dislocation effectively.

Microstructure evolution of semi-solid Mg-14Al-0.5Mn alloys during isothermal heat treatment

Abstract A new Mg-14Al-0.5Mn alloy that exhibits a wide solidification range and sufficient fluidity for semi-solid forming was designed. And the microstructure evolution of semi-solid Mg-14Al-0.5Mn alloy during isothermal heat treatment was investigated. The mechanism of the microstructure evolution and the processing conditions for isothermal heat treatment were also discussed. The results show that the microstructures of cast alloys consist of α-Mg, β-Mg 17 Al 12 and a small amount of Al-Mn compounds. After holding at 520 °C for 3 min, the phases of β-Mg 17 Al 12 and eutectic mixtures in the Mg-14Al-0.5Mn alloy melt and the microstructures of α-Mg change from developed dendrites to irregular solid particles. With increasing the isothermal time, the amount of liquid increases, and the solid particles grow large and become spherical. When the holding time lasts for 20 min or even longer, the solid and liquid phases achieve a state of dynamic equilibrium.

Microstructure transformation of deformed AZ91D during isothermal holding

In order to understand the thermodynamic properties of deformed AZ91D alloy during isothermal holding, the microstructure characteristics and transformation were investigated. The results present that deformation mainly concentrates on the edge of the chips and billets, especially at the interface of α/β. Microstructure transformation mechanism of deformed AZ91D during holding mainly includes recrystallization, spheroidization and Ostwald ripening. The mechanism was then thermodynamically analyzed. During the heating and isothermal holding process, recrystallization driven by residual energy within the deformed AZ91D alloy, spheroidization and Ostwald ripening induced by the reduction of interfacial energy, will inevitably and continuously occur with the extension of heating and holding.

Effect of zinc and mischmetal on microstructure and mechanical properties of Mg-Al-Mn alloy

Abstract Mg-2Al-0.5Mn alloys with 0–0.5% Zn and 0.5%-1.0% La-Ce misch metal (MM) were prepared by metal mould casting method. Effect of alloying elements Zn and MM on microstructures were investigated by X-ray diffraction, optical microstructure and scanning electron microscope. The results showed that Zn and MM additions led to an obvious grain refinement. Addition of 0.5% Zn resulted in about 30% reduction in grain size for Mg-2Al-0.5Mn alloys, while 0.5% MM addition caused about 40% reduction in grain size. The tensile properties of the as-cast alloys were tested at room temperature. Mg-2Al-0.5Mn-0.5Zn-1MM alloy exhibited the best mechanical properties. Improvement of mechanical properties was attributed to the grain-refining effect and the formation of Al 11 MM 3 phase which could inhibit dislocation movement and grain-boundary sliding during deformation.

Effects of cooling rate on bio-corrosion resistance and mechanical properties of Mg–1Zn–0.5Ca casting alloy

Abstract Mg–1Zn–0.5Ca alloys were prepared by traditional steel mould casting and water-cooled copper mould injection casting at higher cooling rate. Microstructure, mechanical properties and bio-corrosion resistance of two alloys were contrastively investigated. Grain size reduces remarkably and microstructure becomes homogenous when raising cooling rate. The bio-corrosion behaviour in 3.5% sodium chloride solution (3.5% NaCl) and Hanks solution at 37°C was investigated using electrochemical polarization measurement and the results indicate that the alloy prepared at higher cooling rates has better corrosion resistance in both types of solution. Further mass loss immersion test in Hanks solution reveals the same result. The reason of corrosion resistance improvement is that raising cooling rate brings about homogeneous microstructure, which leads to micro-galvanic corrosion alleviation. The tensile test results show that yield strength, ultimate tensile strength and elongation are improved by raising cooling rate and the improvement is mainly due to grain refinement.