关键词： AZ31B magnesium Alloy   Asymmetric rolling   Shear deformation   Homogeneity   Twinning   Mechanical properties  

摘要： In this study, the changes in the microstructure, texture, and mechanical properties of the AZ31B magnesium alloy sheet after asymmetric rolling (ASR) in different shear deformations during each pass are reported. A high shear strain is induced along the sheet thickness when the velocity ratio of the upper and lower rollers is 1.8. In the case of the sheet processed via ASR in the reverse shear deformation along the rolling direction (RASR), the grain refinement, weak basal texture, and improved structural homogeneity result in better mechanical properties than those of the sheet processed via symmetric rolling (SR). However, in the case of the sheet processed via ASR in the single shear deformation along the rolling direction (UASR), shear bands containing dynamically recrystallized grains and larger numbers of dislocation are formed, tilting the peak intensity of the pole figure away from the normal direction. Moreover, the shear band with an average grain size of 5 mu m causes severe structural inhomogeneity, which results in bad mechanical properties than the other two sheets. Furthermore, the twin mode changes from the double twin of the SR sheet to the extension twin of the ASR sheet under shear strain. The extension twin contributes to the optimization of the mechanical properties. Finally, the strength and elongation of the sheets processed via RASR are simultaneously improved to 250.3 MPa and 12.5%, respectively.

关键词： Magnesium alloys   High-pressure torsion   AM60   Shear punch test   Texture   Hardness  

摘要： The evolution of the microstructure, crystallographic texture and hardness of an AM60 magnesium alloy was studied in the center and the edge parts of disks processed by high-pressure torsion (HPT) technique at room temperature. In addition, the mechanical properties were also tested by shear punch test (SPT). The number of HPT turns varied between 1/2 and 10. It was found that the grain size of the initial extruded material (similar to 16 mu m) decreased to similar to 2 and similar to 0.8 mu m at the disk center and edge, respectively, even after 1/2 turn of HPT. Ten turns of HPT resulted in further grain refinement to similar to 1 and similar to 0.23 mu m at the disk center and edge, respectively. The dislocation density saturated even after 1/2 turn with the value of similar to 11 x 10(14) m(-2). The maximum value of the hardness was similar to 1300 MPa that was measured at the edge of the disk deformed for 1/2 turn. Despite the practically unchanged grain size and dislocation density, the hardness decreased between 3 and 10 turns which can be explained by texture softening. A good agreement was observed between the yield strength estimated as one-third of the hardness and the values calculated from the dislocation density, grain size and texture. The difference between the microstructure and hardness obtained for AM60 samples processed by HPT and equal channel angular pressing (ECAP) is discussed.

关键词： Magnesium alloy   strain rate   deformation mechanism   LPSO phase   kink band  

摘要： Dynamic compression experiments were carried out on Mg-2.5Zn-4Y magnesium alloy containing long period stacking ordered phase (LPSO) to understand its deformation mechanism using 'Split Hopkinson Pressure Bar'. High strain rates ranging from 700 to 2100 s(-1) were applied along Extrusion Direction. The results demonstrate that maximum compression stress increases with increasing strain rate. In the mean the alloy shows a positive strain rate strengthening effect. The deformation mechanism of Mg-2.5Zn-4Y magnesium alloy with LPSO phase is mainly < c + a > pyramidal slip supplemented with deformation by extension twin in association with kinking of LPSO phase. The impact fracture surface of the investigated magnesium alloy suggested quasi-cleavage fracture.

关键词： AZ91 magnesium alloy   Nanocomposite   Microstructure   Compression   Creep  

摘要： The microstructure, compression, and creep responses of the squeeze-cast AZ91 alloy;the AZ91 alloy with 0.6Sb (wt.%) addition;and the AZ91 alloy with 0.6Sb (wt.%) + 2.0SiC (wt.%) (1.2 vol%) nanoparticles addition have been evaluated. The additions of 0.6Sb and 0.6Sb+2.0SiC to the AZ91 alloy reduce the grain size and decrease the beta-Mg17Al12 phase, and result in improved compression and creep responses. The AZ91 + 0.6Sb+2.0SiCnp nanocomposite exhibits the best compression properties and the highest creep resistance. The dislocation climb controlled by pipe diffusion is the dominant creep mechanism in the alloys and nanocomposite. The superior compression responses are attributed to the reduction in grain size, and the improved creep resistance is attributed to the decrease in the beta-Mg17Al12 phase for both the AZ91 + 0.6Sb alloy and AZ91 + 0.6Sb+2.0SiCnp nanocomposite. The strengthening due to CTE mismatch between the alloy and SiC nanoparticles, as well as the Orowan strengthening for the nanocomposite additionally contributed to the improved compression and creep responses.

关键词： 镁合金   枝晶形貌   择优取向   试验表征   模拟仿真  

摘要： 镁合金被誉为21世纪的绿色工程材料,被广泛应用于汽车、航空航天和3C等领域。枝晶作为金属凝固过程中一种常见的晶体形态,其形貌对铸件的力学性能影响很大。综述了具有密排六方晶体结构的镁合金枝晶生长试验表征与模拟仿真研究进展,阐述了采用试验表征与分析得到的镁合金二维及三维枝晶生长形貌与择优取向,分析了通过建立枝晶生长模型耦合溶质场、温度场、流场、压力场等模拟仿真得出的不同凝固工艺条件对镁合金二维及三维枝晶生长形貌的影响规律,最后指出了当前镁合金枝晶生长试验表征及模拟仿真研究存在的问题及未来的发展方向。

关键词： 高强镁稀土合金   动态再结晶   LPSO相   细晶强化   织构强化  

摘要： 为了满足石油完井可溶压裂球和桥塞的应用需求,需要开发强度超过500 MPa且可工业规模生产的镁合金棒材。在实验室研发的高强度Mg-10Gd-4Y(GW104)合金基础上,添加质量分数为1.32%的Zn元素,采用可工业规模生产的半连续铸造、热挤压和热处理等常规工艺得到GW104+1Zn合金,并系统地研究了Zn元素和各个工艺参数等对GW104+1Zn合金相组成、微观组织和力学性能的影响规律。结果表明,Zn的添加使得合金中存在LPSO相,LPSO相可以抑制动态再结晶的发生,而动态再结晶过程则会吞噬这种LPSO相。小挤压比和低温挤压有利于获得由未完全动态再结晶形成的双峰组织,双峰组织不仅可以提高合金的强度,而且使其断裂伸长率也保持在较高水平。挤压温度为400℃,挤压比为4时,挤压态合金具有最佳综合性能,其屈服强度为307 MPa,抗拉强度为386 MPa,断裂伸长率为7.6%;峰值时效后合金屈服强度为400 MPa,抗拉强度为521 MPa,断裂伸长率为2.1%,满足实际应用需求。

关键词： Dynamic Recrystallization   Localization   Texture  

摘要： The occurrence of continuous dynamic recrystallization in a solutionized WE43 alloy during compressive deformation at 450 degrees C was studied. It was revealed that dynamic formation of second phase particles may exhaust strain-hardening capacity of material, causing the deformation to be concentrated in shear regions. The results showed that prismatic < a > systems play the role as dominant deformation mechanism during shear band formation. The promotion of dislocation activity in this regions assist in the development of low angle boundaries, the misorientation of which is gradually increased with further deformation. The results indicated that, unlike common magnesium alloys, continuous dynamic recrystallization in the RE-containing experimental alloy involves the rotation of grains about non-basal poles. This was discussed relying on the pronounced contribution of non-basal slip during recrystallization of grains within shear regions.

关键词： magnesium alloys   grain boundary sliding   dynamic recrystallization   polycrystal plasticity   texture  

摘要： The aim of present work is to develop a crystal plasticity modeling approach to integrate slip,dynamic recrystallization(DRX)and grain boundary sliding(GBS)for simulating the deformation behavior and texture evolution of magnesium alloys at high ***,the deformation mechanisms of an AZ31B Mg alloy sheet at 300°C were investigated by examining texture and microstructure evolution during uniaxial tension and compression *** refines microstructure at strains less than 0.2,and subsequently GBS plays a significant role during deformation process.A GBS model is developed to evaluate strain and grain rotation induced by GBS,and implemented into the polycrystal plasticity framework *** VPSC-DRX-GBS model can well reproduce the stress−strain curves,grain size,texture evolution and significant texture differences in tension and compression tests due to *** calculated GBS contribution ratio in tension is obviously higher than that in compression due to easier cavity nucleation at grain boundaries under tension loading.

关键词： GWZ1031K镁合金   高温拉伸试验   变形温度   变形行为   LPSO相  

摘要： 通过高温拉伸试验,研究了GWZ1031K镁合金在250~400℃、变形速率为0.2 mm/min条件下的高温变形行为。使用扫描电镜(SEM)、X射线能谱分析(EDS)等方法对微观组织和拉伸断口进行观察。结果表明,在不同温度下,GWZ1031K镁合金的高温拉伸应力-应变曲线均出现峰值,峰值应力随变形温度的升高而减小,而塑性则随着变形温度的升高呈现非线性快速升高,特别是在400℃时合金出现超塑性现象。结合高温力学性能测试对应的微观组织和断口形貌分析可以得出,GWZ1031K镁合金在250~350℃的温度区间内,具有较好耐热性能(高温抗拉强度)。

关键词： Mg Alloy   CMT cladding   FSP   Microstructure   Corrosion   Mechanical properties  

摘要： AZ91 magnesium alloy cladding layer obtained by cold metal transfer technique was subjected to friction stir processing (FSP). The results showed that, after FSP, the grains of the deposited layer were significantly refined, and the coarse beta-Mg17Al12 phase was broken and dispersed into the alpha-Mg matrix, leading to the microstructure modification. Compared with the unprocessed cladding layer, the FSPed samples exhibited better corrosion resistance. Due to the grain refinement and disintegration of the second phase, the tensile strength and elongation of the cladding layer after FSP increased from 233.4 MPa and 5.6% to 278.5 MPa and 13.4%, respectively. (C) 2020 Elsevier B.V. All rights reserved.