Twinning aspects and their efficient roles in wrought Mg alloys:A comprehensive review

Twinning is widely recognized as an effective and cost-efficient method for controlling the microstructure and properties of wrought magnesium(Mg)alloys.Specifically,twins play a crucial role in initiating dynamic recrystallization(DRX),while twin regions experience rapid recrystallization during static recrystallization(SRX).The activation of twinning can lead to changes in lattice orientation,significantly impacting the final texture in Mg alloys.The active roles of twinning are influenced by various factors during the activation process,and the mobility of twin boundaries(TB)can be amplified by stress effects,dislocation interactions,and thermal effects.Conversely,annealing treatments that involve proper segregation or precipitation on TBs serve to stabilize them,restraining their motion.Events such as segregation may also alter the twinning propensity in Magnesium-rare earth(Mg-RE)alloys.While{10–11}contraction twins(CT)and{10–11}-{10–12}double twins(DT)can promote dynamic recrystallization(DRX),they also pose a risk as potential sources of voids and cracks.Additionally,understanding the nucleation and growth mechanisms of twinning is crucial,and these aspects are briefly reviewed in this article.Considering the factors mentioned above,this article summarizes the recent research progress in this field,shedding light on advancements in recent eras.

Stress-corrosion coupled damage localization induced by secondary phases in bio-degradable Mg alloys:phase-field modeling

In this study,a phase-field scheme that rigorously obeys conservation laws and irreversible thermodynamics is developed for modeling stress-corrosion coupled damage(SCCD).The coupling constitutive relationships of the deformation,phase-field damage,mass transfer,and electrostatic field are derived from the entropy inequality.The SCCD localization induced by secondary phases in Mg is numerically simulated using the implicit iterative algorithm of the self-defined finite elements.The quantitative evaluation of the SCCD of a C-ring is in good agreement with the experimental results.To capture the damage localization,a micro-galvanic corrosion domain is defined,and the buffering effect on charge migration is explored.Three cases are investigated to reveal the effect of localization on corrosion acceleration and provide guidance for the design for resistance to SCCD at the crystal scale.

Towards implementation of alloy-specific thermo-fluid modelling for laser powder-bed fusion of Mg alloys

Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion(L-PBF).However,its capabilities for being implemented as a reliable tool for material design,where minor changes in material-related parameters must be accurately captured,is still in question.In the present research,first,a thermo-fluid computational fluid dynamics(CFD)model is developed and validated against experimental data.Considering the predicted material properties of the pure Mg and commercial ZK60 and WE43 Mg alloys,parametric studies are done attempting to elucidate how the difference in some of the material properties,i.e.,saturated vapor pressure,viscosity,and solidification range,can influence the melt pool dynamics.It is found that a higher saturated vapor pressure,associated with the ZK60 alloy,leads to a deeper unstable keyhole,increasing the keyhole-induced porosity and evaporation mass loss.Higher viscosity and wider solidification range can increase the non-uniformity of temperature and velocity distribution on the keyhole walls,resulting in increased keyhole instability and formation of defects.Finally,the WE43 alloy showed the best behavior in terms of defect formation and evaporation mass loss,providing theoretical support to the extensive use of this alloy in L-PBF.In summary,this study suggests an approach to investigate the effect of materials-related parameters on L-PBF melting and solidification,which can be extremely helpful for future design of new alloys suitable for L-PBF.

Effect of characteristics and distribution of Mg_(17)Al_(12)precipitates on tensile and bending properties of high-Al-containing Mg alloys

This study investigates the effect of characteristics and distribution of Mg_(17)Al_(12)precipitates on the uniaxial tensile and three-point bending properties of extruded Mg alloys containing high Al contents.The extruded Mg–9Al–1Zn–0.3Mn(AZ91)alloy contains lamellar-structured Mg_(17)Al_(12)discontinuous precipitates along the grain boundaries,which are formed via static precipitation during natural air cooling.The extruded Mg–11Al–1Zn–0.3Mn(AZ111)alloy contains spherical Mg_(17)Al_(12)precipitates at the grain boundaries and inside the grains,which are formed via dynamic precipitation during extrusion.Due to inhomogeneous distribution of precipitates,the AZ111 alloy consists of two different precipitate regions:precipitate-rich region with numerous precipitates and finer grains and precipitate-scarce region with a few precipitates and coarser grains.The AZ111 alloy exhibits a higher tensile strength than the AZ91 alloy because its smaller grain size and more abundant precipitates result in stronger grain-boundary hardening and precipitation hardening effects,respectively.However,the tensile elongation of the AZ111 alloy is lower than that of the AZ91 alloy because the weak cohesion between the dynamic precipitates and the matrix facilitates the crack initiation and propagation.During bending,a macrocrack initiates on the outer surface of bending specimen in both alloys.The AZ111 alloy exhibits higher bending yield strength and lower failure bending strain than the AZ91 alloy.The bending specimens of the AZ91 alloy have similar bending formability,whereas those of the AZ111 alloy exhibit considerable differences in bending formability and crack propagation behavior,depending on the distribution and number density of precipitates in the specimen.In bending specimens of the AZ111 alloy,it is found that the failure bending strain(ε_(f,bending))is inversely proportional to the area fraction of precipitates in the outer zone of bending specimen(A_(ppt)),with a relationship ofε_(f,bending)=–0.1A_(ppt)+5.86.

Advancements in enhancing corrosion protection of Mg alloys:A comprehensive review on the synergistic effects of combining inhibitors with PEO coating

Magnesium(Mg)alloys are lightweight materials with excellent mechanical properties,making them attractive for various applications,including aerospace,automotive,and biomedical industries.However,the practical application of Mg alloys is limited due to their high susceptibility to corrosion.Plasma electrolytic oxidation(PEO),or micro-arc oxidation(MAO),is a coating method that boosts Mg alloys'corrosion resistance.However,despite the benefits of PEO coatings,they can still exhibit certain limitations,such as failing to maintain long-term protection as a result of their inherent porosity.To address these challenges,researchers have suggested the use of inhibitors in combination with PEO coatings on Mg alloys.Inhibitors are chemical compounds that can be incorporated into the coating or applied as a post-treatment to further boost the corrosion resistance of the PEO-coated Mg alloys.Corrosion inhibitors,whether organic or inorganic,can act by forming a protective barrier,hindering the corrosion process,or modifying the surface properties to reduce susceptibility to corrosion.Containers can be made of various materials,including polyelectrolyte shells,layered double hydroxides,polymer shells,and mesoporous inorganic materials.Encapsulating corrosion inhibitors in containers fully compatible with the coating matrix and substrate is a promising approach for their incorporation.Laboratory studies of the combination of inhibitors with PEO coatings on Mg alloys have shown promising results,demonstrating significant corrosion mitigation,extending the service life of Mg alloy components in aggressive environments,and providing self-healing properties.In general,this review presents available information on the incorporation of inhibitors with PEO coatings,which can lead to improved performance of Mg alloy components in demanding environments.

Effects of Nd and rotary forging on mechanical properties of AZ71 Mg alloys

The effects of Nd addition on the mechanical properties and plastic deformability of AZ71 Mg alloys were investigated.0.5%-2.0%（mass fraction） Nd was added to AZ71 Mg alloys.The grain size and the amount of brittle β-Mg17Al12 phase reduce with increasing the Nd addition,while nanosized AlxNdy precipitates form.In combination with 32% rotary forging and subsequent annealing,the grain size of Nd-added AZ71 Mg alloys reduces greatly from over 350 μm to below 30 μm.Both tensile strength and ductility increase with the Nd addition up to 1.0%.The addition of Nd beyond 1.0% leads to the aggregations of rod-shaped Al11Nd3 and blocky Al2 Nd precipitates,thereby deteriorating both strength and ductility.The 1.0% Nd-added AZ71 Mg alloy shows tensile strength up to 253 MPa and elongation of 10.7%.It is concluded that adding 1.0% Nd to AZ71 Mg alloy yields the optimum toughness,whether under as-cast or rotary forging and annealing conditions.

Superhydrophobic surface of Mg alloys:A review

In the present review,the formation of superhydrophobic(SHP)structures on the surface of Mg alloys was investigated.Different methods including hydrothermal technique,chemical and electrochemical deposition,conversion and polymer coating,and etching routes were discussed.The superhydrophobicity could form on the surface of Mg alloys by the application of different chemical,electrochemical,and physical methods followed by the immersion of these alloys in the solution containing modifying agents including fatty acids or long-chain molecules.The formed morphology,composition,and contact angle were reported and the effect of synthesis route on these characteristics was reviewed.

Biodegradable Mg alloys for orthopedic implants——A review

The last decade has seen a significant growth in the market for alloys used for implants,especially for those intended for orthopedic implants.Research into biodegradable magnesium-based alloys has made great strides in this period,so huge progress has been made in their use in the medical industry.The important factors that led to the intensification of research in this regard,were social but also economic,wanting to improve the quality of life,by reducing the use of conventionally permanent metallic implants(stainless steel,cobalt-based alloys,and titanium alloys)which involve the second implant removal surgery and other undesirable effects(stress shielding and metal ion releases),with a negative impact on the emotional and physical condition of patients,and by significantly reducing the costs for both the patient and the health system in the field of orthopedics.This paper refers to the impact and importance of biodegradable Mg alloys,reviewing the beginning of their development,the significant characteristics that make them so desirable for such applications(orthopedic implants)but also the characteristics that must be modulated(corrosion rate and mechanical properties)to arrive at the ideal product for the targeted application.It highlights,in detail,the mechanism and aspects related to the corrosion behaviour of Mg alloys,electrochemical characterization techniques/methods,as well as strategies to improve the corrosion behaviour and mechanical properties of these types of biodegradable alloys.The means of optimization,the category and the effect of the alloying elements,the design criteria,the requirements that the implants of biodegradable alloys Mg-based must meet and the aspects related to their efficiency are also presented.Finally,the potential applications in the specialized clinics,as well as the final products currently used and made by important prestigious companies in the world are approached.

Alloying design and microstructural control strategies towards developing Mg alloys with enhanced ductility

Nowadays,magnesium(Mg)alloys are promising lightweight structural materials,especially in transportation and aerospace fields,due to their inherent low density and high specific strength.Most of the high-strength Mg alloys exhibit poor formability and ductility at room temperature,which limit their wide applications.However,by proper alloying design and/or delicate microstructural control,some newly developed Mg alloys,including rare-earth(RE)and RE-free ones,show enhanced ductility without significant loss of strength.To identify the critical reasons,recent researches on ductile Mg alloys have been reviewed from the aspects of alloying design strategies and microstructural control via advanced processing technologies.Moreover,some outlooks on enhanced ductility of Mg alloys are suggested,e.g.enhancing the beneficial effect of solute atoms,introducing second phase particles,tailoring bimodal-grained structures,introducing pre-twinning structures,etc.The current research progresses in alloying design and/or novel microstructural control have shed some lights on designing and producing Mg alloys with enhanced ductility.

Stability of twins in Mg alloys-A short review

In this article,the stability of twins,especially{10–12}twins,in Mg alloys was critically reviewed.In the last decade,pre-twinning is considered to be an effective method for adjusting the microstructure and properties of wrought Mg alloys.Especially,formation of twin-texture can remarkably improve formability of rolled Mg alloys.However,the stability of{10–12}twins determines the effect of this method.Previous work revealed that initial{10–12}twins may either grow or shrink under further deformation,and may be removed by static recrystallization under thermal effect.It is considered that improving the stability of twin structure could enhance the contribution of twin-texture on subsequent plastic formability.Based on this background,stress stability and thermal stability of{10–12}twin structure were summarized and reviewed in this article.Finally,a few critical scientific problems in this research field were pointed out.©2020 Published by Elsevier B.V.on behalf of Chongqing University.

Crystallography of precipitates in Mg alloys

Crystallography of precipitates in Mg alloys is indispensable to explain and predict alloy microstructures and properties.In order to obtain a global understanding of diversified experimental results,a general theory of singular interface is introduced,which provides the physical base and calculation methodology for interpreting precipitate morphology and orientation relationship(OR),especially useful for understanding irrational facets and ORs.Guided by the theory,recent experimental findings are systematically summarized,including thermally stable and metastable precipitates with various crystal structures.Then,theoretical advances inspired by the findings are introduced,which deepens our understanding on OR selection and preference of irrational facets.At last,future research directions in this field are proposed.

Effects of pre-aging on microstructure evolution and deformation mechanisms of hot extruded Mg–6Zn–1Gd–1Er Mg alloys

The influence of pre-aging treatment on the microstructure,texture and mechanical properties of the Mg–6Zn–1Gd–1Er(wt.%)alloy was investigated.The microstructure analysis shows that the presence of pre-aging is beneficial to{1012}twin nucleation at the early stage of extrusion and inhibits the growth of twins and promotes the formation of[1010]-fiber texture components,thus accelerating the complex process of recrystallization.In the middle stage of extrusion,the extruded samples under the condition of solid solution were subjected to dynamic precipitation during severe shear deformation.The precipitation of the second phase particles followed the particle stimulating nucleation(PSN)mechanism,which increased the volume fraction of DRX grains during extrusion.In the extruded samples under the peak-aged condition,the particles appear dissolved during the severe shear deformation strain,which slows down the DRX process.In the later stage of extrusion,the small rod-shaped particles followed the PSN mechanism,and finally formed the strong fiber texture.The extruded alloy exhibits the strongest mechanical properties under the peak-aged state,with ultimate tensile strength(UTS)of 346 MPa,tensile yield strength(TYS)of 217 MPa,and elongation to failure(EL)of 13.6%.The improvement of mechanical properties is mainly attributed to the existence of strong fiber texture,small rod-shaped and block-shaped phases.

Dual alloying improves the corrosion resistance of biodegradable Mg alloys prepared by selective laser melting

Mg alloys have been regarded as revolutionary metallic biomaterials for biodegradable bone implants,but their applications are mainly blocked by the too rapid degradation in physiological environment.This study explores the dual alloying effects of Mn and/or Sn on the performance of Mg alloys prepared by selective laser melting.The observed microstructure indicated remarkable refinement of both the grains and intermetallic phases in the Mn-and/or Sn-containing alloys during the rapid solidification process.Moreover,approximately a half decrease in corrosion rate was observed for AZ61-0.4Mn-0.8Sn alloy with respect to AZ61 alloy.The improved corrosion behavior was primarily due to the enhanced protective effects of surface layers,in which Mn-and/or Sn-rich phases acted as a helpful barrier against medium penetration and thereby alleviated the current exchange with the matrix.In addition,the solute Mn and/or Sn positively shifted the corrosion potential,which also brought about a better corrosion resistance.Furthermore,the strength and hardness of the alloys were also effectively improved and comparable to those of cortical bone.This could be ascribed to the dissolved Mn and/or Sn atoms and the finely dispersed intermetallic phases,which might cause lattice distortion and precipitation hardening.Besides,the Mn-and/or Sn-containing alloys showed good cytocompatibility as indicated by the normal morphology and increased viability of MG-63 cells.These findings suggest that the developed AZ61-Mn-Sn alloy is a promising candidate for biodegradable bone implants.

Effects of alloying elements and thermomechanical process on the mechanical and corrosion properties of biodegradable Mg alloys

In this study,four different Mg-Zn-Ca-Mn alloys were produced using gravity die casting method.Mn content was kept constant in all alloys,while Zn and Ca were added in two different ratios.Homogenization heat treatment was applied to all cast alloys and a specimen from each homogenized alloy was hot rolled.Microstructure,mechanical properties,and corrosion behavior of the homogenized and hot rolled alloys were investigated as comparatively.Following results were obtained;grain size decreased significantly with increasing Zn content,Zn promoted Ca 2 Mg 6 Zn 3 phase formation,corrosion resistance increased with increasing Zn/Ca atomic ratio,hot rolling resulted in much higher tensile strength but much lower ductility and toughness.Among the homogenized and hot rolled alloys,ZXM300-h alloy(hot rolled ZXM300 alloy)with its 146±2.5 MPa yield strength,229±3.7 MPa tensile strength,%1.6±0.1 elongation and 0.029 mm/yr.immersion corrosion rate exhibited the best mechanical properties and corrosion resistance to be used as a biodegradable alloy such as fracture bone plate material.

A review of effective strides in amelioration of the biocompatibility of PEO coatings on Mg alloys

Recently,developing bioactive and biocompatible materials based on Mg and Mg-alloys for implant applications has drawn attention among researchers owing to their suitable body degradability.Implementing Mg and its alloys reduces the risk of long-term incompatibility with tissues because of their close mechanical properties and no need for re-operation to remove the implant.Nevertheless,the degradation rate of the implant needs to be controlled because production of hydrogen gas and accumulation of its bubbles increases local pH around the implants.To confine the integrity of implants and the body,the corrosion concern in the body fluid requires to be addressed.Surface modification as one of the effective strategies can improve corrosion resistance.Besides,it creates a suitable surface for bone grafting and cell growth.The development of proper surface-coated implants needs appropriate techniques and approaches.Plasma electrolytic oxidation(PEO)coating can provide long-term protection by providing a ceramic layer and improving the implant’s biocompatibility.Herein,a general review of in-vivo and in-vitro evaluation of PEO coatings on Mg and Mg-alloys has been carried out.Recent advances in surface modification on Mg and Mg-alloys have been discussed,however,the need for reliable laboratory models to predict in-vivo degradation is still valid.

Impressive strides in amelioration of corrosion and wear behaviors of Mg alloys using applied polymer coatings on PEO porous coatings:A review

Magnesium(Mg)and its alloys have received much attention in a lot of areas due to their special chemical and physical properties.Nevertheless,high corrosion rates are a limiting factor.The plasma electrolytic oxidation(PEO)technique is a simple approach to place an oxide film on the surface of light metals like Mg alloys.This method has been considered for controlling the rate of corrosion and improving some other properties.On the other hand,PEO coatings cannot make enough protection of Magnesium alloys for a long time due to porosity and fine cracks.Therefore,PEO-based composite coatings are used to make adequate corrosion protection on the Mg alloys surface.The popularity of these coatings is due to their good corrosion resistance,simplicity,high coating capability,and cost-effectiveness in complex segments.Formation of an organic layer on the surface of PEO coating is one of the effective methods to close the defects and thus prevent the corrosive species penetration into the substrate.Coating the PEO coating with a polymer layer can be a good solution to control the amount of damage and improve the corrosion and abrasion resistance.In addition,PEO coating can eliminate the problems of insufficient adhesion of polymer coatings and is considered as a suitable base for composite coatings.This review paper presents the corrosion and abrasion behavior of the PEO/Polymer dual coating system on Mg alloys.Given the fundamental role of coatings thickness and morphology in wear and corrosion behavior,these aspects have been highly discussed in this study.

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.

Effects of heat treatment on the corrosion behavior and mechanical properties of biodegradable Mg alloys

Biodegradable magnesium(Mg)alloys exhibit great potential for use as temporary structures in tissue engineering applications.Such degradable implants require no secondary surgery for their removal.In addition,their comparable mechanical properties with the human bone,together with excellent biocompatibility,make them a suitable candidate for fracture treatments.Nevertheless,some challenges remain.Fast degradation of the Mg-based alloys in physiological environments leads to a loss of the mechanical support that is needed for complete tissue healing and also to the accumulation of hydrogen gas bubbles at the interface of the implant and tissue.Among different methods used to improve the performance of the biodegradable Mg alloys to address these challenges,it appears that heat treatment is the most effective way to modify the microstructure and thus the corrosion behavior and mechanical properties without changing the composition or shape of the alloys.A desirable combination of corrosion and mechanical properties can be obtained through a precise control of the heat treatment parameters.In this report,the effects of different heat treatments(T4 and T6)on the microstructure,corrosion behavior,and mechanical properties of some of the most important heat-treatable biodegradable Mg alloys(Mg-Zn,Mg-Gd,Mg-Y,Mg-Nd,Mg-Al and Mg-Ag)are examined as well as new perspectives to enhance their clinical implementation.

Thermodynamic database of multi-component Mg alloys and its application to solidification and heat treatment

An overview about one thermodynamic database of multi-component Mg alloys is given in this work.This thermodynamic database includes thermodynamic descriptions for 145 binary systems and 48 ternary systems in 23-component(Mg–Ag–Al–Ca–Ce–Cu–Fe–Gd–K–La–Li–Mn–Na–Nd–Ni–Pr–Si–Sn–Sr–Th–Y–Zn–Zr)system.First,the major computational and experimental tools to establish the thermodynamic database of Mg alloys are briefly described.Subsequently,among the investigated binary and ternary systems,representative binary and ternary systems are shown to demonstrate the major feature of the database.Finally,application of the thermodynamic database to solidification simulation and selection of heat treatment schedule is described.

Coupling physics in machine learning to investigate the solution behavior of binary Mg alloys

The solution behavior of a second element in the primary phase(α(Mg))is important in the design of high-performance alloys.In this work,three sets of features have been collected:a)interaction features of solutes and Mg obtained from first-principles calculation,b)intrinsic physical properties of the pure elements and c)structural features.Based on the maximum solid solubility values,the solution behavior of elements inα(Mg)are classified into four types,e.g.,miscible,soluble,sparingly-soluble and slightly-soluble.The machine learning approach,including random forest and decision tree algorithm methods,is performed and it has been found that four features,e.g.,formation energy,electronegativity,non-bonded atomic radius,and work function,can together determine the classification of the solution behavior of an element inα(Mg).The mathematical correlations,as well as the physical relationships among the selected features have been analyzed.This model can also be applied to other systems following minor modifications of the defined features,if required.