等径角挤压制备AZ91D镁合金的组织与性能

研究了铸态AZ91D镁合金在等径角挤压(Equal Channel Angular Extrusion,ECAE)后的室温力学性能和微观组织特征.在力学性能方面,铸态AZ91D镁合金经过1道次ECAE变形后,室温力学性能(屈服强度、抗拉强度、延伸率、弹性模量)由86.3 MPa,146.3 MPa,1.84%,42.5...     

等径道角 挤压工艺对铸态 AZ91D 镁合金组织的影响

目的介绍等径道角挤压的原理及其对铸态AZ91D镁合金的组织产生的作用。方法通过确定的试验工艺参数,对AZ91D镁合金进行了等径道角挤压变形试验。使用金相显微镜和扫描电镜(SEM),对变形前后的材料进行了显微组织的观察。结果通过进行ECAE挤压后,AZ91D镁合金中的黑色共晶相(Mg17Al12)产生了回溶,在机械剪切和动态再结晶的综合作用下,晶粒得到了细化。结论通过等径道角挤压,能明显改善铸态AZ91D镁合金的组织。     

等径角挤压对AZ31镁合金组织及力学性能的影响

研究了电磁连铸AZ31镁合金沿A路径经常规等径角挤压(ECAE)和两步ECAE变形后的微观组织与力学性能.结果表明:与预挤压态相比,常规ECAE态合金随着挤压道次的增加,晶粒不断细化,伸长率不断提高,但屈服强度与抗拉强度逐渐降低;两步ECAE可以使晶粒进一步细化,伸长率、屈服强度与抗拉强度均提高.伸长率、屈服强度与抗拉...     

稀土Y和Sm对AZ91D镁合金组织与性能的影响

采用控制变量法研究单一稀土Y和复合稀土Y,Sm元素对AZ91D镁合金微观组织与力学性能的影响,分析稀土元素对AZ91D合金的细化机理。结果表明：复合添加稀土Y和Sm对AZ91D合金的作用效果明显好于单一添加稀土Y对AZ91D合金的作用效果,添加Y和Sm后,生成了块状相Al₂Y相和针状相Al₂Sm相,可以作为α-Mg的有效异质形核点。当加入量为0.8%（质量分数,下同）Y+1.0% Sm时,α-Mg晶粒尺寸最为细小,分布最为均匀,其合金的硬度、抗拉强度及伸长率分别为67.42HV,153.37 MPa和3.62%,改善了铸态AZ91D合金的室温力学性能,但是超过这个最佳添加量后,合金的室温力学性能开始下降。     

Influence of equal channel angular extrusion processing parameters on the microstructure and mechanical properties of Mg–Al–Y–Zn alloy

An as-cast Mg–Al–Y–Zn alloy was successfully processed by equal channel angular extrusion (ECAE) in the temperature range of 225–400 °C, and the influences of processing temperature on the microstructure and mechanical properties were investigated. The use of back pressure during one-pass ECAE of Mg–Al–Y–Zn alloy was favorable for eliminating the undeformed area in the billet. At the processing temperature below 250 °C, the microstructures were characterized by unrecrystallised structure and the precipitated phase Mg₁₇Al₁₂ was elongated along the extrusion direction. With increasing processing temperature to 350 °C, a large number of recrystallised grains were obtained. Increasing processing temperature promoted workability but led to decrease in the strength of Mg–Al–Y–Zn alloy. Then billets of as-cast Mg–Al–Y–Zn alloy were extruded at different numbers of ECAE passes. It was found that the microstructure was effectively refined by ECAE and mechanical properties were improved with numbers of ECAE passes increasing from one-pass to four passes. However, strengths decreased slightly after five passes though the grain size decreased considerably.     

等径道角挤压制备高力学性能细晶Mg-6Al合金

为了制备高力学性能细晶Mg-6Al合金坯料,采用金相显微镜、材料拉伸实验机等手段对Mg-6Al合金铸坯进行等径道角挤压实验研究.并利用热处理工艺对挤压后材料进行处理,研究热处理工艺参数对材料力学性能的影响规律.结果表明,Mg-6Al合金的铸坯的抗拉强度为196.4MPa,延伸率为12.6%.经过等径道角挤压的Mg-6Al合金坯料的晶粒被大大细化,其晶粒尺寸由铸坯的140μm左右细化到8μm左右.其力学性能有很大提高,抗拉强度由196.4MPa提高到308.2MPa;延伸率由12.6%提高到30.6%.等径道角挤压工艺是一种非常好的制备高力学性能、细晶Mg-6Al合金的工艺方法.固溶和人工时效热处理工艺对等径道角挤压的Mg-6Al合金坯料的强度有较大影响,对延伸率影响较小.     

SiCp/AZ91D镁基纳米复合材料的室温拉伸行为及塑性变形机理

为得到高强度和高塑性的镁基复合材料,通过高能超声分散法和金属型重力铸造工艺制备了SiC纳米颗粒分散均匀的SiCp/AZ91D镁基纳米复合材料,并进行T4固溶热处理和室温拉伸。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)对试样拉伸后的显微组织和塑性变形机理进行观察与研究。结果表明:T4态SiCp/AZ91D镁基纳米复合材料室温下抗拉强度达到296 MPa,伸长率达到17.3%。经室温拉伸变形后复合材料基体微观组织中出现了大量的孪晶和滑移,孪生和滑移是复合材料塑形变形的主要机制。在室温拉伸过程中,α-Mg基体中SiC纳米颗粒周围形成高应变场,高应变场内形成大量位错和堆垛层错,这些位错和堆垛层错在拉伸应变的作用下演变成大量的滑移带和孪晶,这是SiCp/AZ91D镁基纳米复合材料在室温下具有高塑性的微观塑性变形机理。     

Effects of Ca addition on the microstructure and mechanical properties of AZ91magnesium alloy

The effects of Ca addition on the microstructure and mechanical properties of AZ91 magnesium alloy have been studied. The results show that the Ca addition can refine the microstructure, reduce the quantity of Mg₁₇Al₁₂ phase, and form new Al₂Ca phase in AZ91 magnesium alloy. With the Ca addition, the tensile strength and elongation of AZ91magnesium alloy at ambient temperature are reduced, whereas Ca addition confers elevated temperature strengthening on AZ91 magnesium alloy. The tensile strength at 150°C increases with increasing Ca content. The impact toughness of AZ91magnesium alloy increases, and then declines as the Ca content increases. The tensile and impact fractographs exhibit intergranular fracture features, Ca addition changes the pattern and quantity of tearing ridge, with radial or parallel tearing ridge increasing, tensile strength, elongation and impact toughness reduce.     

Microstructure and Properties of Al-6061 Alloy by Equal Channel Angular Extrusion for 16 Passes

The experimental researches on Equal Channel Angular Extrusion (ECAE) process of commercial available Al-6061 alloy were conducted and the grain refinement after ECAE processing was investigated. Sixteen passes of ECAE processing at room temperature were conducted and the relationship of grain refinement with extrusion pass was established. The property enhancements after ECAE processing including ultimate tensile strength and Vickers microhardness were investigated to determine the effects of the number of ECAE passes on the mechanical properties of the extruded samples. The research presents a whole picture of ECAE processing of the alloy for up to 16 passes.     

Study on tensile properties and microstructure of cast AZ91D/AlN nanocomposites

AZ91D is a widely used magnesium alloy, but its application is generally limited to below 150 °C because of its weak creep resistance and tensile properties at elevated temperatures. In this study, high temperature (200 °C) tensile properties including yield strength and tensile strength of AZ91D are much improved by adding only about 1.0 wt% AlN nanoparticles in the AZ91D matrix through an innovative ultrasonic cavitation based dispersion of nanoparticles. The good ductility of AZ91D is also retained in AZ91D/1%AlN nanocomposites. It is found that ultrasonic cavitation based solidification processing is very effective to disperse AlN nanoparticles in AZ91D melts, which is difficult to obtain by traditional mechanical stirring methods. With a good combination of high temperature yield strength, tensile strength and ductility, AZ91D/1%AlN nanocomposite is promising as a new class of structural materials to be used at temperatures up to 200 °C or higher.     

Effects of Ca combined with Sr additions on microstructure and mechanical properties of AZ91D magnesium alloy

Abstract

Weight reduction to improve automobile fuel economy has triggered renewed interest in magnesium. The effects of Ca/Sr separate and composite additions to AZ91D magnesium alloy on its microstructure and mechanical properties have been investigated. The results indicate Ca can refine both the grain and eutectic phase of AZ91D magnesium alloy. Sr hampers microstructure refinement when composite Ca/Sr additions are made. In addition, separate Ca additions to AZ91D magnesium alloy increase yield strength but decrease elongation of this alloy. By adjusting the Ca/Sr composite proportions, additions to AZ91D magnesium alloy are able to improve both microstructure and mechanical properties of the alloy.     

Microstructure and mechanical properties of rheo-diecast AZ91D magnesium alloy

A new semisolid metal processing technology, rheo-diecasting (RDC) has been developed for production of Mg-alloy components with high integrity. The RDC process innovatively combines the dispersive mixing power of the twin-screw mechanism for creation of high quality semisolid slurry and the high efficiency, low cost nature of the high pressure die casting (HPDC) process for component shaping. AZ91D Mg-alloy was used to optimise the RDC process and to establish its advantages over both the HPDC process and other existing semisolid processing techniques. In this paper we present the RDC process for processing Mg-alloys and the resulting microstructure and mechanical properties of RDC AZ91D alloy. The solidification behaviour of the Mg-alloys in the RDC process and the co-relationships between microstructure and mechanical properties of the RDC AZ91D alloy are discussed. It was found that the RDC process is capable of producing Mg-alloy samples with close-to-zero porosity and a fine, uniform microstructure throughout the entire sample irrespective of the section thickness. Compared with those obtained by other existing processing techniques, the RDC samples have substantially improved or equivalent mechanical properties, with the tensile elongation showing more than 100% improvement.     

Mechanical Behavior Enhancement of AM60/Al2O3p Magnesium Metal–Matrix Nanocomposites by ECAE

The effect of equal channel angular extrusion (ECAE) on the mechanical behavior of AM60/Al₂O_3p magnesium metal–matrix nanocomposites was investigated. ECAE is a useful technique to produce bulk nanostructured materials through severe plastic deformation. The present magnesium metal–matrix composites (Mg MMCs) with 1 wt% nanosized Al₂O₃ particles for ECAE were fabricated using stir-casting method. The significantly enhanced mechanical behavior of AM60/Al₂O_3p magnesium metal–matrix nanocomposites at room temperature, for instance, yield strength (YS), ultimate tensile strength (UTS), and ductility, can be obtained after ECAE process. The AM60/Al₂O_3p MMC after 4 passes of ECAE exhibited greater YS, UTS, and ductility (+135%, +107%, and +245% increase, respectively) than those of as-cast AM60. Experimental results show that the AM60/1wt %Al₂O_3p MMC after 4 passes of ECAE exhibits the superior mechanical behavior.     

Al2O3sf/AZ91D镁基复合材料等径角挤压变形机制研究

为了推动半固态加工在镁基复合材料成形中的应用,采用液态浸渗法制备了增强体体积分数为5%的Al<,2>O<,3sf>/AZ91D复合材料,并采用等径角挤压对其实施变形.利用光学显微镜、扫描电镜和拉伸实验机分别对试样进行了组织观察和力学性能测试,并以此为基础探讨了复合材料在等径角挤压过程中的变形机制.研究表明:Al<,2>...     

等通道挤压AZ80镁合金的析出行为和性能

研究了AZ80镁合金经300℃等通道挤压(ECAP)后的组织、织构与力学性能的演变规律以及第二相析出行为的影响。结果表明:ECAP显著促进了粒状连续析出,可有效节省后续热处理时间。A路径多道次挤压最终获得基面织构;Bc路径挤压后形成基面近似平行于剪切面的织构;第二相析出对ECAP织构特征的形成没有显著影响。用该工艺可获得较高的延伸率(13%-19%),但是抗拉强度过低(300 MPa),综合机械性能不理想。可通过抑制挤压前的未溶粗大粒子的析出、减少挤压道次和降低挤压温度等措施优化AZ80的析出控制。     

Effect of severe plastic deformation on tensile properties and impact toughness of two-phase Zn–40Al alloy

Tensile properties and impact toughness of the severe plastically deformed Zn–40Al alloy were investigated. The material billets were subjected to equal-channel angular extrusion (ECAE). After processing, elongation to failure increased significantly with the increasing number of ECAE passes. ECAE also increased the strength levels after one pass, however, they were reduced with the higher number of passes. The observed softening of the alloy upon multiple ECAE passes was shown to be due to the deformation-induced homogenization and the continuous change in the composition of the constituting phases with the number of passes. In addition, the volume fraction of the hard phase decreased due to dissolution and/or breakage. The impact toughness of the alloy was improved by multi-pass ECAE due to the significant increase in ductility. These findings demonstrate that multi-pass ECAE effectively transforms brittle Zn–Al cast alloys into tougher materials with ductile fracture behavior.     

变形的AZ91D镁合金半固态等温压缩的力学行为

为了了解等径道角挤压(ECAE)的AZ91D镁合金在半固态压缩变形中的力学特征,利用半固态温压缩实验、Gleeble1500实验机和金相显微镜对其在半固态压缩变形中的力学行为进行了研究.结果表明:ECAE的AZ91D镁合金在半固态等温压缩中变形由固相晶粒本身的塑性变形、液相包围着固相晶粒的滑动和转动构成;该材料的真应力-真应变曲线由应力激增阶段、应力下降阶段、稳态阶段和应力增加阶段组成;随保温时间的增加或变形温度的升高,获得相同应变量的真应力明显下降,稳态应力和峰值应力也明显下降;随应变速率的增加,稳态应力增加.     

大塑性变形的AM60镁合金半固态等温处理研究

为了制备晶粒细小且球化程度高的的AM60镁合金半固态坯料,对铸态和等径道角挤压态的AM60镁合金半固态等温处理过程进行了研究.借助金相显微镜对AM60镁合金铸坯和等径道角挤压后的铸坯在半固态等温处理中的微观组织演变进行了观察.研究结果表明:对于AM60镁合金,直接等温处理获得的半固坯晶粒很粗大,其平均晶粒尺寸都在100μm以上,晶粒球化效果不理想,很难获得合格的半固态坯;新SIMA法是一种非常理想制备AM60镁合金半固态坯的方法,利用该方法制备的AM60半固态坯的微观组织晶粒十分细小,平均晶粒尺寸在8～22μm,晶粒球化程度高;随着保温时间的延长,新SIMA法制备的AM60半固态坯的微观组织出现长大现象;随着等温处理温度的升高,固相晶粒的平均尺寸先增加后减小,晶粒球化程度越来越高.     

Evaluating the improvement of corrosion residual strength by adding 1.0 wt.% yttrium into an AZ91D magnesium alloy

The influence of yttrium on the corrosion residual strength of an AZ91D magnesium alloy was investigated detailedly. Scanning electron microscope was employed to analyze the microstructure and the fractography of the studied alloys. The microstructure of AZ91D magnesium alloy is remarkably refined due to the addition of yttrium. The electrochemical potentiodynamic polarization curve of the studied alloy was performed with a CHI 660b electrochemical station in the three-electrode system. The result reveals that yttrium significantly promotes the overall corrosion resistance of AZ91D magnesium alloy by suppressing the cathodic reaction in corrosion process. However, the nucleation and propagation of corrosion pits on the surface of the 1.0 wt.% Y modified AZ91D magnesium alloy indicate that pitting corrosion still emerges after the addition of yttrium. Furthermore, stress concentration caused by corrosion pits should be responsible for the drop of corrosion residual strength although the addition of yttrium remarkably weakens the effect of stress concentration at the tip of corrosion pits in loading process.     

固溶处理对AM60B＋xRE及AZ9lD＋xRE镁合金性能的影响

研究了添加少量富铈混合稀土的AM60B xRE及AZ9lD xRE合金(x＝0．4、0．8、1．2、1．6和2．0％，质量分数)固溶处理后的显微组织与机械性能．结果表明，添加混合稀土能显著提高合金的抗拉强度σb和屈服强度σ0.2，固溶处理明显提高AZ9lD xRE合金的强度；AM60B xRE及AZ9lD xRE合金的铸态组织由α(Mg)固溶体、杆状Al11RE3相、颗粒状Al10Ce2Mn7相以及网状Mg17Al12相组成，经过固溶处理后，网状Mg17Al12相完全溶解，只剩下热稳定性较高的Al11RE3相和Al10Ce2Mn7相，随固溶时间的延长，其形态略有改变．AM60B xRE合金拉伸试样断口呈带局部韧窝的准解理断裂形式，而AZ9lD xRE合金则呈现沿晶断裂 解理断裂的混合断口形态．