Effects of deformation twins on microstructure evolution,mechanical properties and corrosion behaviors in magnesium alloys-A review

Due to lattice reorientation,grain segmentation,induced recrystallization,twins play a very important role in regulating texture,refining grains,improving mechanical properties and corrosion resistance,and has received more extensive attention.Numerous studies have shown that{10-12}<10-11>tensile twins(TTWs)are easily activated in large quantities due to the lower critical resolve shear stresses(CRSS).Introduction of TTWs under uniaxial compression improved the strength,ductility,and formability of magnesium(Mg)alloys.Moreover,TTWs produced by multi-directional impact forging(MDIF)can optimize the microstructure by dividing grains and promoting recrystallization,resulting in significant improvement of mechanical properties.Although{10-11}<10-12>compressive twins(CTWs)and{10-11}-{10-12}double twins(DTWs)can promote dynamic recrystallization(DRX),they are also favorable nucleation sites for cracks.In addition,the type and volume fraction of twins can affect the corrosion resistance,and they also play different roles in the corrosion process of different Mg alloys.Twins have shown great potential for improving structure and properties,but a comprehensive and critical discussion of twins in Mg alloys is still lacking.Therefore,based on previous studies,this article reviews the common types and variants of twins in Mg alloys,influencing factors,and their effects on the microstructure,mechanical properties and corrosion resistance.In addition,some interesting ideas are being proposed for further research.

Numerical and experimental studies on solidification of AZ80 magnesium alloy under out-of-phase pulsed magnetic field

For obtaining the finer grains of magnesium alloy,a novel combined pulsed magnetic field with different initial phases,also called out-ofphase pulsed magnetic field(OPPMF),was applied to study the solidification structure of AZ80 magnesium alloy.The numerical simulation was simultaneously conducted to investigate the refinement mechanisms.The experimental results showed that the macrostructure could be effectively refined by applying external magnetic field.Meanwhile,finer grains were obtained with the higher current intensity.However,the increase of current intensity could only refine the grains to about 0.5 mm.Furthermore,compared to a single pulsed magnetic field(PMF)and alternating series of OPPMF(Connection II),a finer structure was observed when the consecutive series of OPPMF(Connection I)was imposed.In contrast with a single PMF and Connection II,the numerical results showed that the greater axial Lorentz force was obtained under the Connection I,generating the stronger forced flow in the melt.It is believed that abundant nuclei could detach from the mold wall and move faster into the interior melt due to the stronger forced flow;besides,the lower superheat and greater temperature uniformity in bulk melt were realized,accounting for the finest structures under the Connection I.

Boosting the Activity and Stability with Dual-Metal-N Couplings for Li–O_(2)Battery

Electrocatalysts with high efficiency are crucial for improving the storage capacity and electrochemical stability of lithium–oxygen batteries(LOBs).In this work,through a facile hydrothermal method,cobalt–nitrogen-doped carbon nanocubes(Co–N/C),the calcination products of zeolitic imidazolate framework(ZIF–67)are encapsulated by ultrathin C–MoS_(2) nanosheets to obtain Co–N/C@C–MoS_(2) composites which are used as host materials for the oxygen cathode.The synergistic effect between Co–N_(x) active sites and Mo–N coupling centers effectively promotes the formation and decomposition of Li_(2)O_(2) during repeated discharge and charge process.The mesoporous C–MoS_(2) nanosheets with delicately designed morphology facilitate charge transfer and account for improved reaction kinetics and more importantly,suppressed side reactions between the carbon materials and the electrolyte.The oxygen cathode with the Co–N/C@C–MoS_(2)host shows a high initial discharge specific capacity of 21197 mAh g^(-1)and a long operation life of 332 cycles.Theoretical calculation provides in-depth explanation for the reaction mechanism and offers insights for the rational design of electrocatalysts for LOBs.