AZ31镁合金非等温拉深性能的研究

针对AZ31镁合金等温拉深性能差的问题,提出了AZ31镁合金的非等温拉深工艺.通过平底杯形冲头拉深试验研究了不同冲头温度和板料温度对AZ31镁合金非等温拉深性能的影响,确定了使AZ31镁合金具有最佳拉深性能的板料和冲头温度范围.实验结果表明,除了板料和冲头温度之外,拉深速度和润滑条件对AZ31镁合金的非等温拉深性能也有重要影响.     

Microstructure and formability of AZ31B magnesium alloy sheet under continuous pulse current

Utilising electropulsing treatment (EPT) to improve the formability of metals is of paramount importance for engineering applications. The effects of EPT on the microstructure and formability of AZ31B magnesium alloy sheet were investigated. The results indicated that the microstructure and mechanical properties were slightly improved with the increase of current density, while the formability was promoted distinctly. Besides, the formability of the specimen after EPT was better than that of the specimen annealed at the same temperature, which indicated that pulse current can effectively increase the formability of the sheet. Further studies confirmed that the athermal effect caused by the pulse current made great contribution to the dislocation mobility and improved the formability of the sheet.     

AZ31B可降解镁合金的研究

研究了铸态、挤压态及热处理态AZ31B镁合金的力学性能和耐蚀性能，选出性能最优的AZ31B镁合金，植入动物下颌骨处进一步研究其在体内的降解行为及其降解产物对动物体的影响。研究结果表明，AZ31B镁合金经过挤压和固溶时效处理可以提高其力学性能和耐腐蚀性能．将处理后的AZ31B镁合金植入兔下颌骨后发现，材料降解未对动物体造成不良影响，并且降解过程不会影响下颌骨骨折固定的稳定性。因此，可降解AZ31B镁合金有望用于制作下颌骨骨折后的内固定系统。     

Corrosion resistance of biodegradable polymeric layer-by-layer coatings on magnesium alloy AZ31

Biocompatible polyelectrolyte multilayers (PEMs) and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg alloy AZ31. The PEMs, which contained alternating poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), were first self-assembled on the surface of the AZ31 alloy substrate via electrostatic interactions, designated as (PAH/PSS)₅/AZ31. Then, the (PAH/PSS)₅/AZ31 samples were dipped into a methyltrimethoxysilane (MTMS) solution to fabricate the PMTMS films, designated as PMTMS/(PAH/PSS)₅/AZ31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/(PAH/PSS)₅/AZ31 composite film significantly enhanced the corrosion resistance of the AZ31 alloy in Hank’s balanced salt solution (HBSS). The PAH and PSS films effectively improved the deposition of Ca-P compounds including Ca₃(PO₄)₂ and hydroxyapatite (HA). Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg alloys.     

Localized deform behavior of AZ31B magnesium alloy by numerical simulation

The dynamic compression behavior of AZ31B magnesium alloy with hat shaped specimen was investigated at high strain rate in this paper. Based on the Johnson‐cook constitutive model and fracture model, the interaction of temperature, stress and strain fields of AZ31B magnesium alloy with hat shaped specimen were numerically simulated by using ANSYS/LS‐DYNA software under different strain rates, which was validated by experiment. It is found that the plastic strain is highly concentrated on the corner of the hat shaped specimen, which leads to large localized deformation. The voids are nucleated and extended by compression stress. Work harden effect is caused by remained plastic strain, which is located around adiabatic shear band. The stress collapse is discovered in gauge section, which is also discovered in experiment. Thermal soften effect is suppressed with the strain rate increased.     

Rotation friction pressing riveting of AZ31 magnesium alloy sheet

A kind of joining method for magnesium alloys, rotation friction pressing riveting (RFPR), is proposed in this paper. In RFPR operation, a rivet with a plug rotating at high speed is brought to contact with the riveted sheets, generating frictional heat between the rivet and riveted sheets, which softens the sheet materials and enables the rivet to be drilled into the sheets under reduced force. When fully inserted, the rivet is stopped rotating, and the plug is immediately pressed into the shank of the rivet by a punch. The expansive deformation of the rivet shank occurs under the action of the plug, thereby forming a mechanical interlock between the rivet and the sheets to fasten the sheets together. The studies show that RFPR of AZ31 magnesium alloy sheet can be carried out at ambient temperature, and provides the joints with superior shear strength and fatigue property when compared with self-piercing riveting (SPR). The effects of the operating parameters of RFPR process on the quality of the joints were investigated in the study. The results shows that while the rivet rotation speed little affects the shear strength of RFPR joints, the punch pressure has a significant influence on the mechanical properties of the RFPR joints. A numerical analysis was also performed to understand the effect of the punch pressure on the interlock between the rivet and the sheets, and the stress and strain distribution inside the sheet materials around the rivet. The results show that the interlock increased with the punch pressure and there is residual compressive stress inside the sheet materials, which seems to explain the good fatigue property of RFPR joints observed.     

AZ31B镁合金管材热态内压成形性能的研究

为了研究变形镁合金AZ31B管材的热态内压成形性能,通过单向拉伸测试了不同温度和应变速率下其力学性能的变化,通过胀形实验研究了温度对内高压成形性能的影响,以及相应变形条件下微观组织的变化.实验结果表明:在20～300℃时,AZ31B的屈服强度和抗拉强度随着温度的升高而降低,总伸长率随着温度的升高而提高,均匀伸长率随着温度的升高先增大后减小;当应变速率在0.001～0.1s-1时,屈服强度和抗拉强度随应变速率的增大而升高,总伸长率随着应变速率的增大而减小,均匀伸长率随着应变速率的增大先增加后减小;当温度在20～250℃时,镁合金管材的极限胀形率随温度的升高先增大后减小,在175℃时达到最大值.微观组织观察表明,175℃下不完全动态再结晶和孪晶两种微观组织的出现是使镁合金管材极限胀形率提高的主要原因.     

Surface analysis of stationary shoulder friction stir processed AZ31B magnesium alloy

We propose a stationary shoulder friction stir process (SSFSP) to produce a smooth surface finish. The use of a stationary shoulder tool contributes to reducing the heat input during friction stir processing (FSP). Hence, a stationary shoulder tool is advantageous for FSP in heat sensitive alloys like magnesium. The present short communication investigates the surface finish of AZ31B magnesium alloy processed by SSFSP without using additional cooling. Surface analysis of the processed region was carried out by 2D and 3D surface mapping using digital microscopy. The surface mapping indicated that there was very little flash generation on the processed zone, while 3D mapping quantified the surface roughness in the longitudinal as well as transverse directions of the processing zone.     

热挤压工艺对AZ31镁合金晶粒大小及性能的影响

对商用AZ31镁合金挤压棒材进行了不同工艺参数的挤压变形,系统研究了挤压工艺参数对AZ31镁合金晶粒大小以及性能的影响,并对镁合金组织的微晶尺寸进行了金相定量分析.研究结果表明,热变形可有效细化晶粒,但对AZ31镁合金晶粒细化是有限度的;对已通过热挤压变形晶粒细化的AZ31镁合金进一步进行大的塑性变形,其晶粒不但没有进一步的细化反而比挤压前略有长大.     

Temperature evolution analysis of AZ31B magnesium alloy during quasi-static fracture

Fracture toughness of AZ31B magnesium alloy subjected to quasi-static loading was investigated by infrared thermography. The results showed that temperature evolution around the crack propagation path during fracture underwent three stages: initial steady stage, monotonic increase stage and final steady stage. The temperature increase at the beginning of stage II is nearly corresponding to the initiation of unstable crack propagation. And based on this phenomenon, a method applying infrared thermography to estimate fracture toughness of AZ31B magnesium alloy was proposed. Fracture toughness was calculated through infrared thermography, which was in good agreement with the result determined by traditional standard method. Finally, the fracture mechanism was investigated.     

AZ31镁合金棒材循环扭转变形及其对力学性能的影响

在室温条件下,对AZ31镁合金挤压棒材进行循环扭转变形,测试了扭转变形过程的力学性能以及变形后的微观组织和织构特征,并对扭转变形对镁合金棒材的力学性能影响进行了分析。结果表明:镁合金棒材在循环扭转过程中得到了严格对称的应力-应变滞回线,并且随着循环周期的增加,由于加工硬化和内部微裂纹扩展的共同影响,应力-应变滞回线上的应力峰值呈现先增加后减小的特征。在最大扭转角分别为60°和90°条件下,应力峰值出现在第四周期。镁合金棒材扭转变形后的晶粒中出现大量的拉伸孪晶带,孪晶启动使晶粒的 C 轴转向棒材轴线方向。镁合金棒材扭转变形后的力学性能测试结果显示,循环扭转变形明显提高了镁合金棒材压缩变形的屈服强度,其值由扭转前的约100MPa最大提高至约200MPa。     

Dependence of deformation mechanisms on grain orientations and their changes calculated based on Sachs model in magnesium alloy AZ31

During deformation, the orientation of a grain influences not only the deformation mechanisms (slip or twinning) and the specific selection of activated slip or twinning systems for that grain, but also the kinetics of different types of transformation. Schmid factor analysis was applied to determine the orientation dependency of deformation mechanisms in magnesium alloys AZ31 in this work. The orientation changes after the operation of the specific deformation mechanisms were also calculated based on Sachs model. It was found that different deformation mechanisms proceeded differently according to theoretical predictions. Basal slip occurred when basal planes of grains were tilted toward ND around TD. Prismatic slip dominated when basal planes were approximately perpendicular to TD. Calculation results also indicated that the operating of pyramidal 〈a〉 slip can not be neglected. {10 2} twinning was favorable when basal planes were approximately normal to RD and {10 1} twinning was analyzed to be related to the grains with basal orientations. The operating of 〈a + c〉 slip could greatly suppress the activating of twinning by our Schmid factor analysis. Basal orientations with TD and RD scattering can favor basal slip and tension twinning, respectively, after the operation of compression twinning based on the Schmid factor calculations.     

Influence of neodymium on microstructure and mechanical properties of AZ31B wrought magnesium alloy

Abstract

The influences of rare earth neodymium on microstructure and mechanical properties of as cast and hot rolled AZ31B wrought magnesium alloy were investigated. The results show that the mechanical properties of both as cast and hot rolled AZ31B alloys decrease due to Nd addition. Nd reacts with Al to form Al₂Nd phase when Nd is added. Bulky and brittle Al₂Nd intermetallic degrades the mechanical properties. Moreover, the addition of Nd weakens the grain refining effect of Al on as cast AZ31B alloy, resulting in grain coarsening. Coarse grains also cause the decline of the mechanical properties of as cast AZ31B–Nd alloy. The negative influence of the bulky and brittle intermetallics on mechanical properties of AZ31B alloy can be relieved by large deformation because the intermetallics can be sufficiently broken up during the deformation process.     

加工方式对AZ31变形镁合金热拉伸流变应力的影响

针对不同方法制备的AZ31镁合金薄板,利用热拉伸试验机和金相显微镜对其在不同温度和变形速率下的流变应力进行了实验研究.结果表明:挤压、交叉、热轧和冷轧等方法制备的AZ31镁合金薄板的应力-应变曲线基本特征是相同的.峰值流变应力随变形温度的升高和应变速率的降低而降低,在低温时具有明显的厚度效应;当温度大于350℃时峰值流变应力几乎不随板材厚度变化而变化;应变速率小于1.0×10-2s-1,变形温度大于150℃下所有AZ31薄板的延伸率均δ≥45%;单向轧制薄板的各向异性随温度提高减小.     

镁合金AZ31高温形变机制的织构分析

利用X射线衍射和背散射电子衍射方法测定了镁合金AZ3l高温动态再结晶和超塑形变时的宏观和微观织构,分析了晶粒内部的形变机制.结果表明,在动态再结晶和超塑形变过程中,晶粒内部的滑移机制仍起重要作用,表现为再结晶晶粒出现择优取向以及一些晶粒可充分均匀形变成长条状.宏观织构的测定表明,具有不同初始织构的两类样品高温动态再结晶时,新晶粒有不同的取向择优过程,形成相似的织构;长条形变晶粒内部开动的滑移系也有一定的差异.分析了不同温度下相同的织构对应的不同塑变机理取向成像分析表明,基面织构取向的晶粒间总伴随着较高比例的小角晶界和30°(0001)的取向关系,这是六方结构的六次对称性限制了动态再结晶时(亚)晶粒间取向差的有效增大的缘故.     

电轧AZ31镁合金在模拟海水中腐蚀行为研究

为对比研究高能电脉冲轧制工艺和冷轧工艺对AZ31镁合金腐蚀性能的影响,采用腐蚀形貌观察、动电位极化测试、电化学阻抗谱与腐蚀速度测试等方法系统地研究了高能电脉冲轧制和冷轧AZ31镁合金带材在模拟海水(3.5%NaCl)中的腐蚀行为.结果表明:在同样变形量下,与冷轧AZ31镁合金相比,电轧AZ31镁合金的耐腐蚀性略有提高.这与电轧AZ31镁合金再结晶比例大,位错密度小,具有较低能态的位错组态及能形成较稳定的腐蚀产物膜有关.     

Fatigue strength estimation of butt welded joints in magnesium AZ31 alloy using the genetic algorithm

Genetic Algorithm is applied to calculate the substitute structural length (SSL) and obtain the fatigue strength of welded joints in magnesium. Fatigue tests with unnotched and notched specimens of the base material metal (BM), the weld metal (WM) and the heat‐affected zone (HAZ) of magnesium AZ31 (MgAl3) were carried out in order to derive the unknown substitute structural length. Results of fatigue tests with geometrically similar welded joints with full and partial penetration were available. The comparison of the experimental and predicted substitute structural length using Genetic Algorithm Substitute Structural Length Estimation Model (GASLEM) shows that the developed models seem to be capable of predicting the SSL values. Fatigue strength values were also obtained using predicted SSL.     

Development of ternary Mg based alloy for soldering of AZ31B magnesium alloy

Abstract

Two kinds of ternary Mg based alloys were designed to join the AZ31B magnesium alloy plates by high frequency induction soldering with argon shielding gas. The microstructures and properties of the filler metals and joints were investigated by SEM, X-ray diffraction, differential scanning calorimetry, spreading test and tensile test. The results have shown that the microstructures of Mg–31·5Al–10Sn filler metal mainly consist of Mg₁₇Al₁₂, Mg₂Sn and a trace amount of α-Mg phases, while the microstructures of Mg–29·5Zn–1Sn filler metal include α-Mg phase and Mg₇Zn₃ with a trace of α-Mg and Mg₂Sn phases. Both of the filler metals have narrow melting zones; however, the spreading area of the Mg–31·5Al–10Sn filler metal is much larger than that of the Mg–29·5Zn–1Sn filler metal on the AZ31B base metal. The average tensile strength of solder joints with Mg–31·5Al–10Sn filler metal is a little higher than that of the latter solder joints with Mg–29·5Zn–1Sn filler metal.     

Improved properties of friction stir-welded AZ31 magnesium alloy by post-weld heat treatment

Mechanical properties and microstructure of friction stir-welded AZ31 based on variety post-weld heat treatment (PWHT) temperatures were evaluated, and an optimal PWHT condition was identified. At rotational speed of 1200?rev?min^?1 and welding speed of 300?mm?min^?1, the average yield tensile, tensile strength and elongation of friction stir-welded joints was 92.5?MPa, 199.1?MPa and 7.3%, respectively. It was found that (300°C – 1?h) heat treatment after welding was more beneficial than other heat treatments in enhancing the mechanical properties and homogenising grain size. The maximum yield and tensile strength was 139.9 and 238.4?MPa, respectively, tensile longitudinal and compressive transverse residual stress could be effectively eliminated, and the fatigue strength increased 34.2% comparing with as-welded joints.     

AZ31B镁合金带材热轧过程组织均匀性及性能研究

本文开展了变形温度为300、350、400 ℃和总压下率分别为15%、30%、45%、60%的AZ31B镁合金带材热轧试验,分析了不同工艺参数对轧后带材的微观组织及力学性能的影响规律。研究表明:随着轧制温度的升高,再结晶百分数增加,晶粒细化显著,组织均匀性增强;当温度达到350 ℃时,由于中间退火保温导致再结晶晶粒长大,使温度进一步升高,对再结晶程度的影响减弱,轧后带材晶粒度和延伸率均有降低;相比温度参数,提升总压下率对晶粒细化效果更为显著,轧制温度为300 ℃,压下率为60%时近表面平均晶粒尺寸由10 μm细化至3.7 μm,中心层晶粒尺寸细化至4.9 μm,组织分布较为均匀;压下率的增加有效改善了组织均匀性,使轧后带材延伸率显著增加,拉伸断口的韧窝增多,且逐渐加深。