Yong-bing Liu

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.

Effect of Graphite Particle Size on Wear Property of Graphite and Al2O3 Reinforced AZ91D-0.8%Ce Composites

The graphite particles and Al2O3 short fibers reinforced AZ91D-0.8%Ce composites were fabricated by squeeze-infiltration technique. The researches about the effects of different graphite particle sizes on the microstructure and wear property of the composites were performed under the condition of constant contents of graphite particles and Al2O3 short fibers. The results reveal that the grain size of the composites changes less when the graphite particle size descends. Moreover, Ce enriches around the graphite particle and Al2O3 short fibers and forms A13Ce phase with Al element. The graphite that works as lubricant decreases the wear loss. The wear resistance of the composites increases as the graphite particle size increases. At low load the composites have similar wear loss; at high load the composite with the largest graphite particle size has the best wear resistance. The wear mechanism of all the composites at low load is abrasive wear and oxidation wear; at high load, except the composites with the particle size of 240μm whose wear mechanism is still abrasive wear and oxidation wear, the wear mechanism of others changes to delamination wear.

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.

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.

Tensile fracture of as-cast and hot rolled Mg-Zn-Y alloy with long-period stacking phase

Abstract An experimental Mg 97 Zn 1 Y 2 (molar fraction, %) alloy was produced by rolling the as-cast alloy. The microstructure of the alloy is composed of the α -Mg (also marked as 2H-Mg with reference to long-period stacking structure according to hexagonal close packed structure) and long-period stacking (LPS) phase. Tensile tests of Mg 97 Zn 1 Y 2 alloy in comparison with pure Mg were conducted. The fracture morphologies of the tensile specimens were characterized and the microstructures near fracture surface were observed. The results show that the rolled Mg 97 Zn 1 Y 2 alloy shows a mixed fracture mode including dimples indicating a ductile fracture pattern and a small fraction of cleavage planes indicating a brittle fracture pattern, which is different from the single brittle fracture of the as-cast alloy. In addition, the plastic deformation is mainly from dislocations induced strain with small strengthening effect during plastic deformation in the as-cast Mg 97 Zn 1 Y 2 alloy, and the strain hardening rate is similar to that of the as-cast pure magnesium. The deformation mechanism of Mg 97 Zn 1 Y 2 alloy is different from that of the pure magnesium according to a metallographical observation that whether twins are found or not. The strengthening effect hardly exists in the rolled Mg 97 Zn 1 Y 2 alloy under the same dislocations induced strain, which is different from that of the as-cast alloy with moderate strengthening effect.

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.

Microstructure characteristics and solidification behavior of thixomolded Mg-9%Al-1%Zn alloy

Experimental investigation and theoretical analysis of the microstructure of thixomolded AZ91D were carried out to comprehensively understand the morphology transformation of solid particles and the solidification behavior. Typical microstructure of thixomolded AZ91D is composed of α-Mg and β-Mg17Al12, characterized with αun, αprim and eutectic. Four kinds of αun are classified according to the morphology and generation mechanism, such as spherical (α1), irregular (α2), entrapping liquid alloy inside (α3) and entrapping pool inside (α4). Under the effect of heating, shearing, collision, agglomeration or fragmentation, α2 and α4 can be the middle states of α1 and α3. Similarly, α4 and α3 can also break into α2 and become α1 at the end. Controlled by undercooling, αprim nucleates and spherically grows within the remaining liquid alloy of thixomolded AZ91D until instability growth. The investigated microstructure was theoretically proved according to the analysis of Mg-Al binary phase diagram.