Origin of nucleation and growth of extension twins in grains unsuitably oriented for twinning during deformation of Mg-1%Al

A large number of anomalous extension twins,with low or even negative twinning Schmid factors,were found to nucleate and grow in a strongly textured Mg-1Al alloy during tensile deformation along the extruded direction.The deformation mechanisms responsible for this behaviour were investigated through in-situ electron back-scattered diffraction,grain reference orientation deviation,and slip trace-modified lattice rotation.It was found that anomalous extension twins nucleated mainly at the onset of plastic deformation at or near grain boundary triple junctions.They were associated with the severe strain incompatibility between neighbour grains as a result from the differentbasal slip-induced lattice rotations.Moreover,the anomalous twins were able to grow with the applied strain due to the continuous activation ofbasal slip in different neighbour grains,which enhanced the strain incompatibility.These results reveal the complexity of the deformation mechanisms in Mg alloys at the local level when deformed along hard orientations.

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.

Mechanical Behavior and Microstructure Evolution during Tensile Deformation of Twinning Induced Plasticity Steel Processed by Warm Forgings

The mechanical behavior and microstructural evolution of an Fe-30Mn-3Al-3Si twinninginduced plasticity(TWIP)steel processed using warm forging was investigated.It is found that steel processed via warm forging improves comprehensive mechanical properties compared to the TWIP steel processed via cold rolling,with a high tensile strength(R_(m))of 793 MPa,a yield strength(R_(P))of 682 MPa,an extremely large R_(P)/R_(m)ratio as high as 0.86 as well as an excellent elongation rate of 46.8%.The microstructure observation demonstrates that steel processed by warm forging consists of large and elongated grains together with fine,equiaxed grains.Complicated micro-defect configurations were also observed within the steel,including dense dislocation networks and a few coarse deformation twins.As the plastic deformation proceeds,the densities of dislocations and deformation twins significantly increase.Moreover,a great number of slip lines could be observed in the elongated grains.These findings reveal that a much more dramatic interaction between microstructural defect and dislocations glide takes place in the forging sample,wherein the fine and equiaxed grains propagated dislocations more rapidly,together with initial defect configurations,are responsible for enhanced strength properties.Meanwhile,larger,elongated grains with more prevalently activated deformation twins result in high plasticity.

Analyzing topics in social media for improving digital twinning based product development

Digital twinning enables manufacturers to create digital representations of physical entities,thus implementing virtual simulations for product development.Previous efforts of digital twinning neglect the decisive consumer feedback in product development stages,failing to cover the gap between physical and digital spaces.This work mines real-world consumer feedbacks through social media topics,which is significant to product development.We specifically analyze the prevalent time of a product topic,giving an insight into both consumer attention and the widely-discussed time of a product.The primary body of current studies regards the prevalent time prediction as an accompanying task or assumes the existence of a preset distribution.Therefore,these proposed solutions are either biased in focused objectives and underlying patterns or weak in the capability of generalization towards diverse topics.To this end,this work combines deep learning and survival analysis to predict the prevalent time of topics.We propose a specialized deep survival model which consists of two modules.The first module enriches input covariates by incorporating latent features of the time-varying text,and the second module fully captures the temporal pattern of a rumor by a recurrent network structure.Moreover,a specific loss function different from regular survival models is proposed to achieve a more reasonable prediction.Extensive experiments on real-world datasets demonstrate that our model significantly outperforms the state-of-the-art methods.

Strengthening effect of prefabrication(10-12)tensile twinning on AZ80+0.4%Ce magnesium alloy and inhibition mechanism of discontinuous precipitation

This paper provided an effective method to further improve the mechanical properties of the AZ80+0.4%Ce magnesium alloy wheel spoke.The effect of high strength and ductility was obtained with a yield strength of 295.36 MPa,an elongation of 10%,by the combination of pre-deformation(7%deformation)and two-stage aging treatment(120℃/9 h+175℃/24 h).The evolution of the microstructure and properties of the alloy was explored under the coupling conditions of different pre-deformation degrees and multi-stage aging.The results show that,pre-deformation introduced a large number of(1012)tensile twinning and dislocations,which greatly promoted the probability of continuous precipitates(CPs)appearing.On the contrary,the discontinuous precipitates(DPs)were limited by the vertical and horizontal twin structure.As a result,the pre-nucleation method of two-stage aging increased the proportion of CPs by 34%-38%.Owing to the DPs was effectively suppressed,the alloy's yield strength has been greatly improved.Besides,under multi-stage aging,the twin boundaries induce protruding nucleation to form static recrystallization by hindering the migration of dislocations,and the matrix swallows the twins,then the texture gradually tilts from the two poles to the basal plane.As an important supplement,the grain refinement and oblique texture promoted the improvement of the yield strength of the component.

Construction of an Arrhenius constitutive model for Mg-Y-Nd-Zr-Gd rare earth magnesium alloy based on the Zener-Hollomon parameter and objective evaluation of its accuracy in the twinning-rich intervals

According to a high-temperature compression test of rare earth magnesium alloy(WE43),a strain-compensated constitutive model of the Arrhenius equation based on Zener-Hollomon parameters was established,and the rheological behaviors were predicted.The model exhibited relatively serious prediction distortion in the low-temperature and high-strain rate parameter interval,and its accuracy was still unsatisfactory even after modification by a correction operator considering the coupling of temperature and strain rate.The microstructure characterization and statistical analysis showed that a large number of twinning occurred in the parameter intervals with prediction deviation.The occurrence of twinning complicated the local internal stress distribution by drastically changing the crystal orientation and led to significant fluctuations in the macroscopic strain-stress and hardening curves relative to the rheological processes dominated by the dislocation and softening mechanisms,making the logarithm of the strain rate and stress deviate from the linear relationship.This twinning phenomenon was greatly influenced by the temperature and strain rate.Herein,the influence mechanism on twinning behavior was analyzed from the perspective of the interaction of dislocation and twinning.

Twinning behaviors of Mg-Sn alloy with basal or prismatic Mg_2Sn

The Mg-Sn alloys,with basal or prismatic Mg2Sn laths,were employed to reveal the effect of precipitate orientation on twinning behavior quantitatively.The Mg-5wt.%Sn alloys with basal or prismatic Mg2Sn were compressed to study the twinning behaviors.Subsequently,an Orowan strengthening model was developed to quantitatively investigate the critical resolved shear stress(CRSS)increment of precipitates on twinning.The results revealed that the prismatic precipitates hindered the transfer and growth of tensile twins more effectively compared with the basal precipitates.The decreased proportion of tensile twins containing prismatic Mg2Sn might be attributed to a larger CRSS increment for tensile twins compared with that for basal precipitates.The obvious decreased twinning transfer in the alloy with prismatic Mg2Sn could be due to its higher geometrically necessary dislocation and enhanced CRSS of tensile twins.Notably,the prismatic precipitates have a better hindering effect on tensile twins during compression.

Unexpected Twinning and Phase-Transition of the Indentation Standards, Their Transition Energies, and Scientific Dichotomy

The general use of aluminium as an indentation standard for the iteration of contact heights for the determination of ISO-14577 hardness and elastic modulus is challenged because of as yet not appreciated phase-changes in the physical force-depth standard curve that seemed to be secured by claims from 1992. The physical and mathematical analyses with closed formulas avoid the still world-wide standardized energy-law violation by not reserving 33.33% (h2 belief) (or 20% h3/2 physical law) of the loading force and thus energy for all not depth producing events but using 100% for the depth formation is a severe violation of the energy law. The not depth producing part of the indentation work cannot be done with zero energy! Both twinning and structural phase-transition onsets and normalized phase-transition energies are now calculated without iterations but with physically correct closed arithmetic equations. These are reported for Berkovich and cubecorner indentations, including their comparison on geometric grounds and an indentation standard without mechanical twinning is proposed. Characteristic data are reported. This is the first detection of the indentation twinning of aluminium at room temperature and the mechanical twinning of fused quartz is also new. Their disqualification as indentation standards is established. Also, the again found higher load phase-transitions disqualify aluminium and fused quartz as ISO-ASTM 14577 (International Standardization Organization and American Society for Testing and Materials) standards for the contact depth “hc” iterations. The incorrect and still world-wide used black-box values for H- and Er-values (the latter are still falsely called “Young’s moduli” even though they are not directional) and all mechanical properties that depend on them. They lack relation to bulk moduli from compression experiments. Experimentally obtained and so published force vs depth parabolas always follow the linear FN = kh3/2 + Fa equation, where Fa is the axis-cut before and after the phase-transition branches (never “h2” as falsely enforced and used for H, Er and giving incorrectly calculated parameters). The regression slopes k are the precise physical hardness values, which for the first time allow for precise calculation of the mechanical qualities by indentation in relation to the geometry of the indenter tip. Exactly 20% of the applied force and thus energy is not available for the indentation depth. Only these scientific k-values must be used for AI-advises at the expense of falsely iterated indentation hardness H-values. Any incorrect H-ISO-ASTM and also the iterated Er-ISO-ASTM modulus values of technical materials in artificial intelligence will be a disaster for the daily safety. The AI must be told that these are unscientific and must therefore be replaced by physical data. Iterated data (3 and 8 free parameters!) cannot be transformed into physical data. One has to start with real experimental loading curves and an absolute ZerodurR standard that must be calibrated with standard force and standard length to create absolute indentation results. .

分子量对PA1012及其复合材料性能的影响

以三种不同分子量及分子量分布的长碳链AABB型偶-偶尼龙1012(PA1012)为原料,探究了分子量及分布对纯PA1012以及PA1012/玻璃纤维(GF)复合材料结构与性能的影响。对不同分子量及分子量分布的PA1012的基础物理性能、热力学性能以及结晶行为进行表征和分析,结果表明,高分子量和宽分子量分布的PA1012具有更高的韧性、更小的热变形温度和更大的模塑收缩率。与GF复合后,PA1012/GF复合材料的力学性能和耐热性能相较于纯PA1012得到大幅提高,同时吸水率和收缩率明显下降。高分子量和宽分子量分布会降低PA1012/GF复合材料的结晶能力,有利于复合材料的韧性提高,使其刚性和耐热性能下降,纵向/横向收缩率差值增加。实际应用中如对材料刚性有较高要求,可选择分子量低/分子量分布窄的PA1012产品;若要求材料具有较高韧性,可选择分子量高/分子量分布宽的PA1012产品。

基于Twin Builder的110kV油浸式变压器3维磁场降阶模型及损耗分析

为解决3维变压器磁场有限元仿真计算效率低的问题,提出基于本征正交分解法的磁场降阶模型与基于二次多项式的损耗响应面模型。以1台110 kV变压器为算例,首先建立了考虑绕组涡流损耗的变压器磁场仿真模型,通过仿真分析了其在额定工况下的磁场及损耗分布;其次,通过仿真试验设计获取了多组工况下的磁场与损耗数据,在Twin Builder中训练得到变压器磁场的各降阶模块;最后,搭建面向数字孪生应用的变压器3维磁场降阶模型,实现了变压器磁场损耗的快速计算与云图分布的可视化。与计算单数据相比,仿真结果考虑了涡流效应的绕组损耗在靠近端部时有明显升高,最大值分别出现在高、低压绕组两端,约为绕组中部损耗的1.3~1.65倍。基于该磁场结果建立的降阶模型在计算效率方面较全阶模型有显著提升,将实际仿真时间缩短至0.76s,可满足数字孪生应用场景下的磁场快速计算需求。

螺旋扩弓器联合Twin-block矫治器早期矫治在青少年下颌后缩中的应用效果及对气道形态的影响研究

目的探讨螺旋扩弓器联合Twin-block矫治器早期矫治在青少年下颌后缩中的应用效果及对气道形态的影响研究。方法将河南大学赛思口腔医院2021年5月至2022年5月收治的63例青少年下颌后缩患者,根按照随机数字表法分为两组,对照组(32例)、观察组(31例),对照组早期给予Twin-block矫治器治疗,观察组早期给予螺旋扩弓器联合Twin-block矫治器矫治治疗,观察两组牙齿角度相关指标、气道形态指标及舌骨位置变化。结果矫治前,两组上下齿槽座角(ANB)、颅底-下齿槽座角(SNB)、前下中切牙下颌平面(T-MP)、颅底-上齿槽座角(SNA)比较差异无统计学意义(P>0.05),矫治后3个月,观察组ANB、SNB、T-MP、SNA均大于对照组(P<0.05);矫治前,两组后鼻脊-咽顶点距(PNS-R)、软腭后-软腭后咽壁距(SPP-SPPW)、后鼻脊-上咽壁距(PNS-UPW)、会厌骨-下咽壁距(V-LPW)比较差异无统计学意义(P>0.05),矫治后3个月,观察组PNS-R、SPP-SPPW、PNS-UPW、V-LPW均大于对照组(P<0.05);矫治前,两组舌骨-眶耳平面距(H-FH)、舌骨-下颌平面距(H-MP)、舌骨-颈椎前平面距(H-VL)、舌骨-颅底平面距(H-S)比较差异无统计学意义(P>0.05),矫治后3个月,观察组H-FH、H-MP、H-VL、H-S均大于对照组(P<0.05)。结论螺旋扩弓器联合Twin-block矫治器早期矫治可以有效改善青少年下颌后缩患者牙齿角度、气道形态,纠正舌骨的位置,改善通气功能。

On the strengthening and slip activity of Mg-3Al-1Zn alloy with pre-induced{1012¯}twins

{1012¯}twins were introduced into the magnesium(Mg)plate AZ31 via pre-rolling along its transverse direction.The plates,both with and without the pre-induced{1012¯}twins,were subjected to uniaxial tension along different directions.Using crystal plasticity modeling,we found that the strengthening effect of the pre-induced{1012¯}twins on the macroscopic flow stress primarily arised from the increased slip resistance caused by the boundaries,rather than the orientation hardening due to the twinning reorientation(although the latter did make its contribution in some specific loading directions).Besides,the pre-existing{1012¯}twins were found,by both experiments and simulation,to promote the activity of prismatic and pyramidal<c+a>in the parent matrix of the material.Further analysis showed that the enhanced non-basal slip activity is related to the{1012¯}twin boundaries’low micro Hall-Petch slope ratios of non-basal slips to basal slip.With the critical resolved shear stress(CRSS)obtained from crystal plasticity modeling and the orientation data from EBSD,a probability-based slip transfer model was proposed.The model predicts higher slip transfer probabilities and thus lower strain concentration tendencies at{1012¯}twin boundaries than that at grain boundaries,which agrees with the experimental observation that the strain localization was primarily associated with the latter.The present findings are helpful scientifically,in deepening our understanding of how the pre-induced{1012¯}twins affect the strength and slip activity of Mg alloys,and technologically,in guiding the design of the pre-strain protocol of Mg alloys.

Twin-block在骨性Ⅱ类错[牙合]下颌后缩患儿中的应用

目的:探讨Twin-block在骨性Ⅱ类错[牙合]下颌后缩患儿中的应用效果。方法:选取2019年1月-2021年1月笔者医院接收的84例骨性Ⅱ类错[牙合]下颌后缩患儿设置为研究对象,按随机抽签法分为对照组、研究组,各42例,对照组采用直丝弓矫治器,研究组采用Twin-block矫治器。比较两组治疗前后咀嚼功能、牙齿咬合力、下颌骨变化、软组织面型变化、上气道矢状径,并统计家属治疗满意度。结果:治疗后,研究组咀嚼功能、牙齿咬合力、下颌骨变化指标、软组织面型变化指标均优于对照组(P<0.05);治疗后,研究组上气道矢状径高于对照组(P<0.05);研究组家属治疗满意度(95.24%)明显高于对照组(73.81%)(P<0.05)。结论:Twin-block应用于骨性Ⅱ类错[牙合]下颌后缩患儿治疗中,能改善咀嚼功能,增强牙齿咬合力,促进下颌骨生长,提高面型美观度,扩大上气道矢状径,利于改善呼吸功能,获得家属对治疗效果的高度评价。

Twin-Block双期矫治与单纯直丝弓矫正技术在早期下颌后缩矫正患儿中的疗效对比

目的探讨Twin-Block双期矫治与单纯直丝弓矫正技术在替牙及恒牙早期错(牙合)畸形矫正患儿中的疗效对比。方法选取我院2020年9月到2023年9月收治的60例恒牙早期错(牙合)畸形患儿作为研究对象,按照治疗方法不同分为观察组与对照组,各组均为30例。所有患儿均采取矫正治疗,对照组患儿采取直丝弓矫正技术进行治疗,观察组患儿采取Twin-Block矫治器及直丝弓矫治技术进行双期治疗。对比两组患儿临床疗效,及矫治时间,治疗前头影测量及关节改建情况,采用口腔锥形束扫描成像进行检测两组患儿关节窝宽径、关节前间隙、关节后间隙、关节上间隙、髁突前后径、髁突高度相关参数表达水平,最后对比两组患儿治疗前后上下齿槽座(ANB)角、下齿槽座(SNB)角、上齿槽座(SNA)角、下颌平面角(Mp-SN)、下颌综合长度(Ar-Po)、下颌升支高度(Ar-Go)、下颌体长(Go-Gn)、上中切牙-SN平面角(U1-SN)、下中切牙-下颌平面角(L1-Mp)、上唇审美平面距(Ls-E)、下唇审美平面距(Li-E)、鼻唇角。结果观察组治疗总有效率96.67%明显高于对照组76.67%(P<0.05);治疗后,观察组矫治时间长于对照组(P<0.05);治疗前,两组患儿关节窝宽径、关节前间隙、关节后间隙、关节上间隙、髁突前后径、髁突高度对比无明显差异(P>0.05),治疗后,两组患儿关节窝宽径对比无明显差异,关节前间隙减小,观察组(1.21±0.28)mm高于对照组,关节后间隙、关节上间隙、髁突前后径、髁突高度均增加,且观察组高于对照组(P<0.05);治疗前,两组患儿ANB角、SNB角、SNA角、Mp-SN、Ar-Po、Ar-Go、Go-Gn、U1-SN、L1-Mp、Ls-E、Li-E、鼻唇角对比无明显差异(P>0.05),治疗后,两组患儿SNB、Mp-SN、Ar-Po、Ar-Go、Go-Gn、鼻唇角均增大,ANB、U1-SN、L1-Mp、Li-E、Ls-E减小,且观察组变化大于对照组(P<0.05)。结论Twin-Block矫治器配合直丝弓矫治技术双期矫治器与单纯直丝弓矫正技术相比治疗替牙及恒牙早期错(牙合)畸形疗效显著,可作为儿童恒牙早期错(牙合)畸形的首选治疗方案。

Origin of extension twinning-mediated static recrystallization and unique parallel alignment of(0001) poles to transverse direction in Mg-3Al-0.4Mn(mass%) alloy sheet

The origin of unique parallel alignment of(0001) poles to transverse direction(TD) was investigated using Mg-3Al-0.4Mn(mass%)alloy sheets rolled with different process conditions. When rolling was performed with intermediate reheating, the alloy showed a sluggish static recrystallization(SRX) behavior during post-annealing, facilitating the nucleation and growth of statically recrystallized grains from extension twins. This resulted in the apparent texture component with the parallel alignment of the(0001) poles to the TD, and the sheet exhibited good ductility for both the rolling direction(RD) and TD. In contrast, continuous rolling without intermediate reheating led to the formation of severely deformed regions near double twins. SRX was promoted at such regions, forming a typical basal textural feature with weak RD-split of the(0001) poles. Although extension twins were formed after the continuous rolling, SRX was facilitated at the severely deformed regions with double twins, and the formation of the unique alignment of the(0001) poles to the TD was suppressed. The RD-split texture led to the large elongation to failure along the RD, while it along the TD decreased owing to the narrow distribution of the(0001)poles toward the TD, resulting in the in-plane anisotropy in ductility.

Underlying slip/twinning activities of Mg-xGd alloys investigated by modified lattice rotation analysis

The inconsistencies regarding the fundamental correlation between Gd content and slip(twinning)activities of Mg alloys appeal further investigations.However,the traditional slip dislocations analysis by TEM is time-consuming,and that by SEM/EBSD cannot recognize the partial slip modes.These urge a more efficient and comprehensive approach to easily distinguish all potential slip modes occurred concurrently in alloy matrix.Here we report a modified lattice rotation analysis that can distinguish all slip systems and provide statistical results for slip activities in Mg alloy matrix.Using this method,the high ductility of Mg-Gd alloy ascribed to the enhanced non-basal slips,cross-slip,and postponed twinning activities by Gd addition is quantitatively clarified.

Acceleration of aging behavior and improvement of mechanical properties of extruded AZ80 alloy through(10–12) twinning

The effects of pre-existing {10–12} extension twins on the precipitation behavior of an extruded AZ80 material during aging and on its mechanical properties after peak aging are investigated. The material containing {10–12} twins-which are formed by compression before aging(twinned material)-has a finer grain size and higher dislocation density than the extruded material. Although the peak hardnesses of the twinned and extruded materials are almost the same, the time to reach the peak hardness is considerably shorter in the former material than in the latter(4 h and 24 h, respectively). In the twinned material, the high dislocation density of the {10–12} twins promotes continuous precipitation, which results in the formation of numerous fine Mg17Al12precipitates within the twins in the early stage of aging.The formation of these continuous precipitates reduces the driving force for discontinuous precipitation, which consequently suppresses the formation and growth of coarse Mg17Al12precipitates at the grain boundaries. Despite its shorter peak-aging time, the 4 h-peak-aged twinned material shows higher tensile strength and elongation than the 24 h-peak-aged extruded material. These higher mechanical properties of the former material are attributed primarily to the presence of more abundant fine continuous precipitates, which are effective in strengthening the material, and less abundant coarse discontinuous precipitates, which can act as crack initiation sites. These results demonstrate that the introduction of {10–12} twins into wrought Mg–Al-based alloys can accelerate the Mg17Al12precipitation kinetics considerably and improve the strength and ductility of the peak-aged alloys simultaneously.

一步法制备长碳链尼龙1012及其性能

传统熔融缩聚法制备尼龙通常先制备尼龙盐以提高单体热稳定性、保证酸胺的物质的量比,再进行后续的聚合。而长碳链尼龙由于其单体分子量较大、热稳定性较好,因此可以省略繁琐的成盐工艺,具备一步法熔融缩聚的可能性。笔者通过一步法成功制备了长碳链尼龙1012 (PA1012),探究了预聚工艺、后聚工艺以及终聚工艺对产物性能的影响,得出了适合一步法制备PA1012的最佳聚合参数:预聚时间2.5 h,预聚温度190℃,后聚时间1 h,后聚温度240℃,终聚时间根据制品需要选择合适的时间。随后进一步探究了在190℃下预聚阶段和240℃下后聚阶段PA1012的聚合动力学参数,其反应速率常数分别为16.66 g/(mol·min)和90.01 g/(mol·min)。利用傅里叶变换红外光谱仪和核磁共振氢谱对产物结构进行了表征,结果表明成功合成了PA1012;利用差式扫描量热仪、热重分析仪分析了PA1012的热性能,结果表明PA1012具有良好的耐热性和热稳定性;对PA1012进行力学性能测试,结果表明PA1012力学性能优异。以上结果证明通过一步法合成新型长碳链PA的可行性和高效性。

Implications of twinning on the microstructure development,crystallographic texture and mechanical performance of Mg alloys-a critical review

Deformation twinning is profusely activated in the Mg alloys due to lower critical resolved shear stress(CRSS) compared to the non-basal slip systems(prismatic and pyramidal ) and plays a significant role in texture reorientation, grain refinement and enhancement of mechanical performance. Twinning is a sequential process comprising twin nucleation, twin propagation and twin growth, hence several intrinsic and extrinsic parameters that facilitate or suppress the process have been critically reviewed. The dependence of twinning on the grain size, deformation temperature, favorable grain orientation and shear strain have been thoroughly discussed in the context of published literature and an attempt has been made to provide a benchmark conclusive finding based on the majority of works. Furthermore, the subsequent effect of twinning on the mechanical performance of Mg alloys, including ductility, formability and tension-compression asymmetry has been discussed in detail. Lastly, the stability of twins, including stress and thermal stability, is summarized and critical issues related to pertinent bottlenecks have been addressed.

Assessing the predictive capabilities of precipitation strengthening models for deformation twinning in Mg alloys using phase-field simulations

Precipitation strengthening is a key strategy for improving the overall mechanical properties of Mg alloys. In Mg-Al alloys, basal precipitates are known to strengthen against twinning, resulting in an increase in the critical resolved shear stress(CRSS) necessary for continued deformation. Although several models have been proposed to quantify the influence of precipitate shape, size, and distribution on the CRSS, the accuracy, scope, and applicability of these models has not been fully assessed. Accordingly, the objectives of this study are:(i)to analyze the accuracy of analytical models proposed in the literature for precipitation strengthening against twin thickening and propagation(in Mg-Al alloys) using phase-field(PF) simulations,(ii) to propose modifications to these model forms to better capture the observed trends in the PF data, and(iii) to subsequently test the predictiveness of the extended models in extrapolating to experimental strengthening data.First, using an atomistically-informed phase-field method, the interactions between migrating twin boundaries(during the propagation and thickening stages) and basal plates are simulated for different precipitate sizes and arrangements. In general, comparison of the increase in CRSS determined from the PF simulations and the predictions from four precipitation strengthening models reveals that modifications are necessary to the model forms to extend their applicability to precipitation strengthening against both twin thickening and propagation. A subsequent comparison between predictions from the extended models and experimental strengthening data for peak age-hardened samples reveals that the(extended) single dislocation and dislocation wall models provide reasonably accurate values of the increase in CRSS.Ultimately, the results presented here help elucidate the fidelity and applicability of the various hardening models in predicting precipitation strenghtening effects in technologically important alloys.