Microstructure design of advanced magnesium-air battery anodes

Metal-air battery is an environmental friendly energy storage system with unique open structure.Magnesium(Mg)and its alloys have been extensively attempted as anodes for air batteries due to high theoretical energy density,low cost,and recyclability.However,the study on Mg-air battery(MAB)is still at the laboratory level currently,mainly owing to the low anodic efficiency caused by the poor corrosion resistance.In order to reduce corrosion losses and achieve optimal utilization efficiency of Mg anode,the design strategies are reviewed from microstructure perspectives.Firstly,the corrosion behaviors have been discussed,especially the negative difference effect derived by hydrogen evolution.Special attention is given to the effect of anode micro-structures on the MAB,which includes grain size,grain orientation,second phases,crystal structure,twins,and dislocations.For further improvement,the discharge performance,long period stacking ordered phase and its enhancing effect are considered.Meanwhile,given the current debates over Mg dendrites,the potential risk,the impact on discharge,and the elimination strategies are discussed.Microstructure control and single crystal would be promising ways for MAB anode.

The mechanisms of grain growth of Mg alloys:A review

Grain growth directly influences the plasticity and strength of Mg alloys.As the grain size decreases from the microscale to the nanoscale,the plasticity of Mg alloys continually increases,whereas the strength first increases and later decreases.These trends are observed because the plastic deformation mechanism changes from dislocation–twinning dominance to grain boundary dominance.In this study,the factors influencing grain growth,such as the temperature of plastic deformation/annealing,second-phase particles and solute atoms,are examined to aid effective control of the grain size.Additionally,the mechanisms of grain growth,typically induced by strain and thermal activation,are clarified.Strain-induced grain boundary migration is attributable to the difference in the strain energy stored in adjacent grains with high-density dislocations.Heat-induced grain boundary migration is driven by the difference in the energy of the grain boundary/subgrain boundary and boundary curvature.Abnormal grain growth can be induced by anisotropy of the strain energy,anisotropy of the grain boundary mobility,depinning of the second phase and high misorientation gradient.

Solid-state bonding process induced highly synergistic mechanical properties of 6061 Al alloy joint by shear deformation

Obtaining a highly synergistic mechanical property between joint and base metal(BM)in aluminum(Al)alloy is a chronic problem.In this work,shear bonding technology is applied to a commercial 6061 Al alloy.The results show that a flat and uniform joint interface is obtained.The joint presents a highly synergistic mechanical property compared with BM,whether after shear bonding or heat treatment.The joint coefficient reaches 95.6%after shear bonding and exceeds 100%after heat treatment,which is better than the traditional connection method of aluminum alloy.The high joint coefficient mainly originates from the well-linked joint and gradient grain structure.The gradient grain structure is beneficial to activate more slip systems to coordinate plastic deformation.Although the fine-grained structure is sacrificed after heat treatment,higher strength and joint coefficient are obtained due to the higher work hardening.This newly developed method has a large potential for application to the infinite rolling of Al alloy sheets and can also be used for Al alloy connection in automobile,aerospace,rail transportation,and other fields.The findings in this work can provide essential theoretical support and application reference for the shear connection of Al alloy.

Effect of the width on AZ31 sheet rolling

A pyramid sheet has been used in experiments and three-dimensional finite element simulation to study the edge cracks and effects of width on AZ31 sheet under rolling. Results show that the edge cracks of Mg sheet comply with the Normalized Crockroft ＆ Latham theory. It can be predicted by D=-0.124＋0.09X - 0.008X2, if D ;〉 0, the edge cracks occur. The sheet shearing deformation at the edge brings about cracks. The strain rate changes periodically with different X. With initial width increases, the recrystallized grain size decreases. The finite element model has been validated by the experiment results.

Transformation of Laves phases and its effect on the mechanical properties of TIG welded Mg-Al-Ca-Mn alloys

The effects of Al content and Ca/Al mass ratio on the microstructure and mechanical properties of tungsten inert gas(TIG)welded Mg-2Ca-x Al-0.5Mn(x=0,1,5)alloy joints were studied in present work.Results showed that increasing Al content was effective in reducing the dendrite spacing at the fusion zone(FZ)edge.The Laves phases in the FZ and the heat-affected zone(HAZ)can be changed from Mg_(2)Ca to(Mg,Al)_(2)Ca with the decrease of Ca/Al ratio,and the(Mg,Al)_(2)Ca could be further transformed to Al_(2)Ca under welding thermal cycle.Furthermore,dynamic dissolution and precipitation of Laves phases and Al_(8)Mn_(5)phases occurred in the HAZ,resulting in a gradient microstructure and hardness peak in this area.The tensile properties of the joints were significantly improved with the increase of Al content,which was mainly due to the modification of Laves phases.

Effects of Different Stretching Routes on Microstructure and Mechanical Properties of AZ31B Magnesium Alloy Sheets

AZ31B magnesium alloy sheets were stretched by 13% along three different routes： the extrusion direc- tion （Route A）, 45° to the extrusion direction （Route B） and the transverse direction （Route C）, and then were annealed at 350℃ for 60 min. The microstructure and texture, tensile mechanical properties and formability were investigated at room temperature. The results indicated that all the three stretched samples exhibited weakened basal texture, compared with the as-received sheet due to static recrystallization. By comparison, Route B processed sample showed the most dispersive basal texture, while Route A pro- cessed specimen exhibited the lowest basal intensity. Improved mechanical properties for the stretched and annealed sheets with different stretching routes were achieved. Furthermore, Route A processed sheet showed the highest Erichsen value compared with the samples processed along Route B and Route C.