挤压态AZ31B镁合金在超塑变形过程中的微观组织及力学性能研究

通过正向温挤压获得了细晶微观组织的AZ31B镁合金。研究了在310～460℃范围内,应变速率1×10-3～1×100/s下的超塑性流变行为。结果表明,在415℃、1×10-3/s的条件下AZ31B镁合金具有良好的超塑性,最大延伸率可达380%。应变速率敏感指数达到0.47。通过光学显微镜和扫描电镜（SEM）分别观察了AZ31B镁合金在超塑变形过程中的微观组织演变和断口形貌。晶界滑移机制为AZ31B超塑变形的主要机制。     

AZ31变形镁合金性能与组织的研究

对商业化的AZ31B和AZ31D变形镁合金挤压后的型材进行取样,对其拉伸性能、断口形貌和金相组织进行了观察。结果表明：挤压后的镁合金发生了动态再结晶,生成了细小的等轴晶粒,从而提高了材料的强度和塑性加工性能,其中AZ31D镁合金的塑性提高得更大。在此基础上进一步对镁合金的变形机制进行探讨。     

7B04铝合金超塑变形空洞研究

在530℃、3×10-4/s条件下对细晶和粗晶(平均晶粒尺寸8μm和16μm)两种7B04铝合金板材进行了不同变形量的高温拉伸实验,对空洞的演化进行了表征,结合超塑变形机理比较和分析了晶粒尺寸对空洞行为的影响.结果表明:超塑变形过程中空洞平均直径基本呈线性增长,空洞体积分数呈指数规律增长,细晶板材中空洞的发展较为缓慢.实验用7B04铝合金对空洞的容忍度约为16%.细晶组织在变形过程中较易发生协调运动,获得了良好的超塑性.绘制了空洞长大机理图,求得扩散控制和塑性控制的空洞长大机理间的转换半径约为1. 6μm.     

AZ31B镁合金铸轧板的织构和冲压性能的分析

在室温条件下,AZ31B镁合金的塑性加工难度较大,而影响其加工难度的主要因素就是AZ31B镁合金的织构以及冲压性能。基于此,笔者自制AZ31B镁合金铸轧板,分别制备了普通AZ31B镁合金以及复合能场AZ31B镁合金铸轧板,对两者的织构与冲压性能进行了分析,分析的结果显示,普通AZ31B镁合金铸轧板的织构强度更大,冲压性能相对较差。     

AZ31镁合金板在不同温度下轧制中的数值模拟

运用DEFORM-3D软件,模拟了在250~400℃温区内不同温度下轧制变形量为30%的AZ31镁合金板材的轧制过程,分析了温度对镁合金板材轧制过程中轧制力、等效应力以及温度场分布的影响。研究结果表明:AZ31镁合金板材在轧制过程中存在着明显的温度效应,并且随着轧制温度的升高,温度效应减弱;随着轧制温度的升高,AZ31镁合金板材在轧制过程中的塑性变形抗力、轧制力与等效应力均显著降低;若单从温度角度考虑,在其他条件不变的前提下最佳轧制温度在350~400℃的温区内。     

基于FEM分析轧制预变形对AZ31B镁合金热轧板材边部损伤的影响规律

基于FEM(finite element method)研究了轧制预变形对AZ31B镁合金热轧板材边部损伤的影响规律。选用Normalized Cockcroft&Latham损伤模型,在轧制温度为400℃、轧制速度为0.5 m·s^-1的条件下,对规格为50 mm×20 mm×15 mm的AZ31B镁合金板材预先使用凸度轧辊制备不同形状的板坯,使板坯中部的变形量一致,边部比中部分别高出2,4和6 mm,然后分别进行多道次、小压下率和单道次、大压下率平辊轧制模拟仿真。结果表明,轧制预变形能够显著降低镁合金板材边部的损伤,经多道次轧后板材边部的拉应力减小,应力三轴度降低,边部与中部的应变差值减小,边部金属与中部金属流动趋于同步,且在预设仿真方案范围内边部凸度越大,轧后板材边部的损伤值越小,最小损伤值为0.729。对镁合金板材预变形后可实现单道次、大压下率轧制,板材的边部温度和应变速率均有所增加,有利于降低轧制过程中的边部损伤。研究结果可为少或无边裂镁合金板材轧制工艺制定提供理论依据。     

AZ31镁合金的研究现状

综述了国内外对AZ31镁舍金的研究现状。讨论了主要合金元素对AZ31镁合金的组织和性能的影响,介绍了AZ31镁合金的晶粒细化、塑性成形技术的研究现状。对AZ31镁合金的发展前景进行分析。     

AZ31B镁合金准静态拉伸断裂准则

使用万能材料试验机,通过板材的无缺口拉伸试件和缺口拉伸试件,研究了AZ31B镁合金在室温下的准静态拉伸力学性能。结合数值模拟分析了各试件拉伸过程,解释了缺口处的断裂失效原理,获得了应力三轴度与断裂应变的关系,拟合得到了AZ31B镁合金准静态拉伸断裂准则。     

变形AZ31镁合金数控加工工艺参数的选择研究

镁合金作为新型的轻质高强矿产资源,目前被广泛应用于军事、医疗、卫生等领域,是现阶段最具有发展潜力的金属材料之一。传统的镁合金加工工艺受到人为能力影响,工作效率低,能源浪费大,整个加工过程时间较长。为此,提出一种变形AZ31镁合金数控加工工艺参数,通过研究变形AZ31B的加工参数,改变原有镁合金加工过程的切割焊接等行为,对镁合金的冷却和加热产生的非晶化行为进行研究,得到了变形AZ31镁合金数控加工过程中的最佳工艺参数。仿真实验表明,提出的新的数据加工工艺比传统方法在材料的抗腐蚀性、坚固程度、加工时间、加工效率等多个方面都得到了改善。     

热轧AZ31镁合金薄板的室温成形性

针对AZ31镁合金板材室温冲压成形较差的特点,采用不同轧制温度获得镁合金板材,使用半球形凸模胀形,绘制镁合金室温成形极限图并分析轧制温度对镁合金板材组织和室温成形能力的影响.发现AZ31镁合金板材的成形性能不仅与晶粒尺寸有关,还与晶粒取向有关.基面织构的减弱可明显提高板材的胀形性能,在基面织构强度相似的情况下,晶粒尺寸对板材的成形性能起决定性影响.      

Experimental and Numerical Study of Electromagnetic Forming of AZ31B Magnesium Alloy Sheet

Wrought magnesium alloys are interesting materials for automotive and aeronautical industries due to their low density in comparison to steel and aluminium alloys, making them ideal candidates when designing a lower weight vehicle. However, due to their hexagonal close‐packed (hcp) crystal structure, magnesium alloys exhibit low formability at room temperature. For that reason, in this study a high velocity forming process, electromagnetic forming (EMF), was used to study the formability of AZ31B magnesium alloy sheet at high strain rates. In the first stage of this work, specimens of AZ31B magnesium alloy sheet have been characterised by uniaxial tensile tests at quasi‐static and dynamic strain rates at room temperature. The influence of the strain rate is outlined and the parameters of Johnson‐Cook constitutive material model were fit to experimental results. In the second stage, sheets of AZ31B magnesium alloy have been biaxially deformed by electromagnetic forming process using different coil and die configurations. Deformation values measured from electromagnetically formed parts are compared to the ones achieved by conventional forming technologies. Finally, numerical study using an alternative method for computing the electromagnetic fields in the EMF process simulation, a combination of Finite Element Method (FEM) for conductor parts and Boundary Element Method (BEM) for insulators, is shown.     

基于Gurson模型的镁合金板材温热冲压成形研究

在Gurson损伤模型的基础上,采用有限元数值模拟与温热冲压实验相结合的方法,对镁合金板材温热冲压成形过程中的材料损伤过程进行了预测.考虑了板材的塑性各向异性行为,通过用户自定义材料子程序VUMAT将损伤模型嵌入到有限元软件ABAQUS/Explicit中.采用单轴拉伸试验数据与有限元数值模拟结果进行迭代,确定了Gurson模型所需要的材料参数.使用ABAQUS模拟得到了镁合金板材温热冲压过程中微孔洞的演变及分布规律.通过扫描电子显微镜,对不同温度下的AZ31镁合金板材由孔洞增长和聚合引起的内部损伤演化进行了观察分析.研究结果表明,板材中微孔洞的分布与实验数据相吻合,说明本文所提出的方法可以应用于金属板材温热冲压成形性能预测.      

非线性组合硬化条件下镁合金板料变形回弹预测

变形回弹作为金属板料成形的主要缺陷之一,如何提高变应变路径条件下的回弹预测精度一直是研究者们面临的难题.本文针对镁合金变形特点,提出了同时考虑同向硬化、动态硬化和屈服圆畸变的本构模型.以0.8 mm厚AZ31B镁合金板料为研究对象,施加不同预拉伸后进行弯曲变形试验,观察了不同预变形对回弹规律的影响.同时结合有限元分析ABAQUS-Explicit (Vumat)和ABAQUS-Implicit (Umat)对板料的变形及回弹过程进行模拟仿真,对比试验与模拟结果,验证动态硬化对于镁合金板料变形回弹的重要影响.      

Microstructure and mechanical properties of friction stir welding of AZ31B magnesium alloy added with cerium

The AZ31B magnesium alloy sheet added with 0.5 wt.% Ce was welded with friction stir welding(FSW).The microstructures and mechanical properties of the welded joint were investigated.The results showed that the microstructures in the weld nugget zone were uniform and with small equiaxed grains.The grains in the heat-affected zone and the thermo-mechanical affected zone were coarser than those in the base metal zone and the weld nugget zone.The ultimate tensile strength of AZ31B magnesium alloy added with 0.5...     

Effects of SiCp Parameters on Microstructures,Interface Structure and Mechanical Property of Mg Bulk Composites Produced by Ultrasonic Vibration Processing

In this study, the effects of submicron silicon carbide particulates (SiCp) addition on microstructures of the SiCp/AZ31B composites prepared by stir casting combined with ultrasonic vibration, as well as on the interface and the tensile behavior of AZ31B alloy were discussed. Most of the SiCp tended to aggregate in the last solidified regions (such as grain boundaries) during solidification. Microstructural characterization of the developed magnesium matrix composites also revealed significant grain refinement. The grain of composite was refined by increasing particle volume fraction. Moreover, better interfacial bonding was realized in the composite. Tensile test results showed that strengths of the submicron SiCp/AZ31B composites were enhanced significantly whilst as the amount of submicron SiCp were increased, the strengths of the SiCp/AZ31B composites also increased.     

Friction Stir Lap Welding of Magnesium Alloy to Steel: A Preliminary Investigation

An initial study was made to evaluate the feasibility of joining magnesium alloy AZ31 sheet to galvanized steel sheet in a lap configuration using friction stir welding (FSW). Two different automotive sheet steels were used for comparative evaluation of the dissimilar joining potential: a 0.8 mm thick, electrogalvanized (EG) mild steel, and a 1.5 mm thick hot-dipped galvanized (HDG) high-strength, low-alloy (HSLA) steel. These steels were joined to 2.33 mm thick AZ31B magnesium sheet. A single FSW tool design was used for both dissimilar welds, and the process parameters were kept the same. The average peak load for the AZ31-1.5 mm steel weld joint in lap shear mode was found to be 6.3 ± 1.0 kN. For the AZ31-0.8 mm steel weld, joint strength was 5.1 ± 1.5 kN. Microstructural investigation indicates melting of the Zn coating present on the steel sheets, and subsequent alloying with the Mg sheet resulted in the formation of a solidified Zn-Mg alloy layer.     

Mechanical Properties of Gradient Structure Mg Alloy

In this work, a surface mechanical attrition treatment (SMAT) process was applied to AZ31B magnesium alloy at room temperature. This method produced a gradient structure on the treated AZ31B, in which the grains of the topmost layer are refined to nanoscale sizes. A combination of nanocrystallites at the surface and coarse-grains in the center are the main features of this structure. This structure results in an excellent combination of both strength and ductility. The highest yield strength for the 30 minutes SMAT AZ31B samples increased to 249 ± 5 MPa and the uniform elongation decreased to 9.3 ± 0.8 pct, whereas the original yield strength was only 147 ± 4 MPa and the uniform elongation was 15.4 ± 1.1 pct. Microstructural observations, stress relaxation tests, and hardness tests were used to verify the results. Additionally, there is a specific volume fraction of gradient structure to achieve the best mechanical performance, which is shown to be in the range of 9.3 to 14 pct for the AZ31B alloy.     

Constitutive Behavior of Commercial Grade ZEK100 Magnesium Alloy Sheet over a Wide Range of Strain Rates

The constitutive behavior of a rare-earth magnesium alloy ZEK100 rolled sheet is studied at room temperature over a wide range of strain rates. This alloy displays a weakened basal texture compared to conventional AZ31B sheet which leads to increased ductility; however, a strong orientation dependency persists. An interesting feature of the ZEK100 behavior is twinning at first yield under transverse direction (TD) tensile loading that is not seen in AZ31B. The subsequent work hardening behavior is shown to be stronger in the TD when compared to the rolling and 45 deg directions. One particularly striking feature of this alloy is a significant dependency of the strain rate sensitivity on orientation. The yield strength under compressive loading in all directions and under tensile loading in the TD direction is controlled by twinning and is rate insensitive. In contrast, the yield strength under rolling direction tensile loading is controlled by non-basal slip and is strongly rate sensitive. The cause of the in-plane anisotropy in terms of both strength and strain rate sensitivity is attributed to the initial crystallographic texture and operative deformation mechanisms as confirmed by measurements of deformed texture. Rate-sensitive constitutive fits are provided of the tensile stress–strain curves to the Zerilli–Armstrong[1] hcp material model and of the compressive response to a new constitutive equation due to Kurukuri et al.[2]     

Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity–temperature–composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg₂Ni, and Al₃Ni₂ intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg₂Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.     

Mg-Gd-Y与AZ31两种变形镁合金的冲击波响应

利用平行平面正碰撞方法产生的冲击波对Mg-Gd-Y与AZ31两种典型变形镁合金加载,并对回收后的材料进行准静态压缩实验,采用金相显微镜和透射电子显微镜进行微观组织分析。冲击波加载后,原始固溶态Mg-Gd-Y合金的屈服强度增加了21 MPa,而时效峰状态合金的屈服强度仅增加4 MPa,时效处理后产生的析出相β’使合金的屈服强度增加幅度明显减少;然而,AZ31镁合金的屈服强度增加了40 MPa。Mg-Gd-Y与AZ31镁合金的冲击波加载后力学响应的差异取决于冲击波过程中两者所具有的不同变形机制,冲击波变形后Mg-Gd-Y合金中的孪晶体积分数非常少,其变形机制以位错滑移为主。相比之下,冲击波加载后的AZ31合金中产生了大量孪晶,孪生是该合金的一种重要变形机制。孪晶界在后续再加载过程中成为位错滑移的障碍,从而导致AZ31镁合金表现出更为显著的冲击波强化效果。