循环扩挤变形AZ80镁合金的组织、织构与力学性能

采用循环扩挤(Cyclic expansion-extrusion,CEE)变形工艺对AZ80镁合金的块状材料进行热挤压加工,观察试样的微观组织与织构,并测试了力学性能。结果表明:AZ80镁合金经过CEE变形后,晶粒的尺寸明显细化,第4道次CEE变形之后,晶粒尺寸从150~230 μm细化至2 μm,整体分布均匀且呈等轴晶;2道次变形后,随着挤压道次的增加,晶粒的细化程度减慢;同时经过CEE变形的AZ80镁合金织构包括了(0001)基面平行于挤压方向与(1120)棱柱面垂直于挤压方向的两种不同纤维织构,随着挤压道次的增加,织构总体强度出现先减后增再减的变化;力学性能相对于均匀化态有着明显的变化,第1道次CEE变形之后,抗拉强度与屈服强度分别达到各自的最大值,为290 MPa和180 MPa,第2道次CEE变形之后,强度出现不随晶粒细化而增强的现象(反Hall-Petch理论),这是因为织构的软化作用强于晶粒的细化作用,而伸长率随着挤压道次的增加而提高。     

加工工艺对AZ61镁合金拉压不对称性的影响

采用一次挤压变形、二次挤压变形以及一次挤压后再进行锻造的三种加工工艺对AZ61镁合金进行塑性变形,研究不同的加工工艺对镁合金力学性能及拉压不对称性的影响。结果表明:挤压变形可以细化AZ61镁合金的晶粒,而在挤压后进行锻造变形,会使得其晶粒长大粗化。二次挤压后,由于强化了{0002}基面织构,AZ61镁合金的拉伸屈服强度增加,压缩屈服强度下降,使得拉压不对称性加大。而一次挤压后锻造,在挤压基面织构状态得到改变,且由于晶粒粗大,从而总体上使得AZ61镁合金的拉伸屈服强度下降,而压缩屈服强度几乎保持不变,AZ61的拉压不对称性得到改善。     

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.     

连续变断面循环挤压AZ31镁合金的微观组织与力学性能

采用连续变断面循环挤压技术(CVCE)对AZ31镁合金进行循环挤压。采用光学显微镜、电子拉伸机等设备,分析变形前及不同循环道次后AZ31镁合金的微观组织和力学性能。结果表明:AZ31镁合金经10循环CVCE后,平均晶粒尺寸由变形前25.3μm有效细化到5.5μm;伸长率提高到34.3%,抗拉强度下降到200MPa。由于晶粒细化效应,导致α相主要变形机制由1循环的孪生变为随后道次的位错滑移。抗拉强度的降低与挤压后(0001)晶面取向分布的分散性有关;伸长率的增大与晶粒细化和滑移面的激活有关。     

累积叠轧工艺对AZ31镁合金板材组织和性能的影响

采用累积叠轧工艺对AZ31 镁合金薄板进行剧塑性变形,研究了累积叠轧变形过程中镁合金板材的组织及性能演变.实验结果表明,累积叠轧可以有效细化AZ31镁合金板材的晶粒组织,显著改善室温延伸率,是制备大尺寸、高性能细晶镁合金板材的一种有效、经济而且可以实现工业化生产的技术.累积叠轧5道次后AZ31镁合金板材组织均匀,晶粒尺寸为1～2μm左右,晶粒细化源于大的累积变形及表面剪切变形;室温抗拉强度和延伸率可达到349MPa和22.46%,可归因于晶粒细化对镁合金强度和塑性的改善.累积叠轧板材的道次间的加热使ARB组织粗化,减小了累积叠轧过程中晶粒持续细化的效果.     

挤压-剪切工艺挤压AZ31镁合金的组织和织构演变

采用大变形技术"挤压-剪切"(Extrusion-shear,ES)工艺挤压AZ31镁合金并研究其组织和织构演变.结果表明:经ES工艺挤压后能得到细小均匀的再结晶晶粒;其宏观组织内存在多种类型的织构,削弱了基面织构的主导地位;由极图可知{0002}基面织构强度下降,ES工艺的再结晶机制是连续动态再结晶.     

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。     

对双峰织构类型AZ31镁合金板材力学性能各向异性的分析

目的 制备双峰织构类型的AZ31镁合金板,以改善板材微观组织和弱化基面织构,研究微观组织对力学性能各向异性的影响规律,以提高镁合金板材的成形性能。方法 通过弯曲限宽矫直技术对0°、30°和60°轧向切样的板材进行热加工以预制拉伸孪晶,获得双峰织构类型的AZ31镁合金板材,通过EBSD获取板材的微观组织。对RD、45°和TD方向的原始板材进行室温单向拉伸实验,获得板材的工程应力-应变曲线及力学性能参数,并计算r值（塑性应变比）与n值（应变硬化指数）。结果 弯曲限宽矫直技术可诱发大量拉伸孪晶形成ED偏转织构,将偏转织构与基面织构共存的板材称为双峰织构类型AZ31镁合金板材。拉伸孪晶的出现显著细化了晶粒,弱化了基面织构强度,使板材的屈服强度下降,极大提升了材料塑性。其中30°轧向切样的板材ND面塑性力学性能各向异性的改善效果最好,其r值最小、n值最大。结论 双峰织构类型能够弱化AZ31镁合金板材基面的织构强度,提高材料塑性。拉伸孪晶含量越高,板材的强度与塑性越好,力学性能各向异性的改善效果也越显著。     

AZ31镁合金不同挤压速度下的组织演变及力学性能研究

目的 针对AZ31镁合金材料在挤压成形过程中变形较为困难的问题,研究AZ31镁合金在不同挤压速度下的微观组织和力学性能演化规律。方法 采用DEFORM–2D软件对0.5、3、12、20 mm/s这4种挤压速度下材料挤压变形过程中的材料流动趋势、应变场、应力场和温度场等进行数值模拟和分析。结果 AZ31镁合金材料的挤压温度场随着挤压速度的增加显著升高,不同速度挤压后坯料的温度模拟值与实验结果实测值的变化趋势吻合。随着挤压速度的增大,材料的晶粒尺寸先增大后减小,0.5、3、12、20 mm/s这4种速度挤压后的晶粒尺寸分别为1.0、0.9、1.4、1.1 μm,变形材料的加工硬化率呈现出先增大后减小的趋势。在0.5 mm/s的挤压速度下,材料内部的微观组织均匀性较差,然而强度较高,抗拉强度约为416 MPa;在挤压速度为12 mm/s时,合金的晶粒组织最均匀,同时其综合力学性能较好,屈服强度为220 MPa,伸长率为17.3%,其加工硬化率也达到最大,为0.184。结论 通过DEFORM数值模拟能够为镁合金挤压变形提供指导。对于镁合金挤压变形,采用较低的挤压速度(约0.5 mm/s)对AZ31镁合金进行挤压变形,能够获得强度较高、伸长率相对偏低的挤压棒材,采用较高的挤压速度(约12 mm/s),则更有利于获得综合性能优良的镁合金挤压棒材。     

挤轧复合变形制备电磁连铸AZ61板材

通过挤压后再轧制的方法制备AZ61镁合金板材,利用动态再结晶产生局部剪切变形减弱挤压形成的{0002}基面织构,可以有效提高板材的塑性成形能力,对比分析了直接轧制75%变形量与挤轧复合轧制60%变形量的AZ61电磁半连铸镁合金板材.结果表明,两种工艺方法所得到的板材力学性能相近,前者抗拉强度σb=300 MPa,屈服强度σ0.2=230 MPa,延伸率δ=8.0%,后者σb=295 MPa,σ0.2=245 MPa,δ=8.2%.因此,可以通过挤轧复合的工艺方法利用较小的轧制变形量(60%)制备出与较大轧制变形量(75%)性能相近的镁合金板材.     

Improving tensile and compressive properties of magnesium alloy rods via a simple pre-torsion deformation

A simple method has been developed in order to improve the tensile and compressive properties of extruded AZ31 rod. The strategy is to apply pure shear strain to the extruded rods by a pre-torsion deformation. It is found that pre-torsion exhibits little influence on the shape and size of AZ31 rod, however largely enhances tensile and compressive yield strength and reduces yield asymmetry along extrusion direction. With increasing twisted angle, the compressive yield strength exhibits gradually increase, and the tensile yield strength exhibits a non-monotonous change. The changes in tensile and compressive properties are ascribed to the proliferation of dislocations, the generation of twin lamellae and the weakening of extrusion texture during pre-torsion. The corresponding mechanisms are addressed and discussed.     

Dynamic recrystallization behavior of AZ31 magnesium alloy processed by alternate forward extrusion

One of the important factors that affect the microstructure and properties of extruded products is recrystallization behavior. Alternate forward extrusion (AFE) is a new type of metal extrusion process with strong potential. In this paper, we carried out the AFE process experiments of as-cast AZ31 magnesium alloy and obtained extrusion bar whose microstructure and deformation mechanism were analyzed by means of optical microscopy, electron backscattered diffraction and transmission electron microscopy. The experimental results indicated that homogeneous fine-grained structure with mean grain size of 3.91 μm was obtained after AFE at 573 K. The dominant reason of grain refinement was considered the dynamic recrystallization (DRX) induced by strain localization and shear plastic deformation. In the 573-673 K range, the yield strength, tensile strength and elongation of the composite mechanical properties are reduced accordingly with the increase of the forming temperature. Shown as in relevant statistics, the proportion of the large-angle grain boundaries decreased significantly. The above results provide an important scientific basis of the scheme formulation and active control on microstructure and property for AZ31 magnesium alloy AFE process.     

Microstructures and mechanical properties of ultrafine-grained Ti/AZ31 magnesium matrix composite prepared by powder metallurgy

The microstructure of ultrafine grain for magnesium alloys can result in drastic enhancement in their room temperature strength, but the issue of low strength at elevated temperature becomes more serious as well due to grain boundary slide. Here ultrafine-grained Ti/AZ31 magnesium matrix composites with high strength at both room and elevated temperature were prepared by vacuum hot pressing and subsequent hot extrusion. The microstructure of the composite samples before and after consolidation processing was characterized, and the mechanical properties of the as-consolidated bulk samples were measured at room and elevated temperatures. The results indicate that after extrusion ultrafine-grained magnesium alloys were obtained and Ti particulates with particulate size of ～310?nm disperse in Mg matrix. The magnesium grain of AZ31-15at.%Ti grows from 66?nm to 800?nm. Meanwhile, the relative densities of Ti/AZ31 composites are higher than 99%. The yield strength (YS) of extruded AZ31-15at.%Ti composite at room temperature is 341?MPa, being 2.4 times higher than original AZ31 alloy. Theoretical estimation shows that remarkably enhanced room-temperature mechanical strength attributes to grain boundary strengthening with the contribution ratio of 74%. In addition, the peak stress of extruded AZ31-15at.%Ti composite at 573?K is 82?MPa and ultrafine Ti dispersions are responsible for the enhanced strength.     

Microstructure and mechanical behaviour of asymmetric extruded Mg–3Al–1Zn alloy sheets

Abstract

Microstructural evolution and mechanical responses of Mg–3Al–1Zn (AZ31) sheet processed by the asymmetric extrusion (ASE) and conventional extrusion (CE) are examined. Mechanical properties of ASE sheets were remarkably enhanced compared with CE samples. This is attributed to the subdivision of the asymmetric extrusion die along the flow passage equipped with a chamfer on one side, which would trigger the angular spread of the basal texture by introducing an asymmetry shear deformation. Moreover, subsequent annealed ASE specimens show a significant weakening of the basal texture and a combination of the superior stretch formability.     

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。     

New Technique of Casting-rolling Strips for Semi-solid Magnesium Alloys

The conjugation of semi-solid process technique and casting-rolling technique applied to produce the magnesiumstrips was studied in this paper.The purpose is to gain the high quality magnesium alloy strips with non-dendriticstructure and to solve the processing problems of magnesium alloy strips to a certain degree.The project includes the following aspects:setting up an experimental device;preparing the semi-solid slurry;optimizing the casting-rolling techniques of magnesium alloy studying th…     

搅拌摩擦加工对AZ31镁合金微观组织及力学性能的影响

采用搅拌摩擦加工技术(Friction stir processing,FSP)对AZ31镁合金板材进行了单道次加工,研究了加工区域微观组织对力学性能的影响。结果表明,相同前进速度下,旋转速度升高,平均晶粒尺寸增大。搅拌摩擦加工后,晶粒尺寸和织构变化显著影响AZ31镁合金的力学性能,平均晶粒尺寸越大,越易发生孪生变形。织构类型主要包括基面织构和纤维织构。基面织构位于软位向时,屈服强度降低,但纤维织构会弱化基面织构对力学性能的影响。     

挤压包覆轧制对SiCP增强镁合金(AZ91)复合板显微组织和力学性能的影响

通过热挤压复合的方式将AZ91合金引入至SiC_P增强镁合金（AZ91）（SiC_P/AZ91）复合材料中,制备出厚度为2 mm的AZ91-（SiC_P/AZ91）复合板,研究了热轧对其显微组织和力学性能的影响规律。研究结果表明:AZ91的引入显著提高了SiC_P/AZ91的轧制成形能力。与AZ91层相比,SiC_P/AZ91层内晶粒尺寸小,硬度高。随轧制压下量的增加,AZ91-（SiC_P/AZ91）复合板晶粒尺寸变大,析出相数量减少且尺寸增大,导致硬度呈现下降的趋势。与挤压态AZ91-（SiC_P/AZ91）复合板相比,当压下量为50%时,轧制态AZ91-（SiC_P/AZ91）复合板屈服强度由272 MPa提高至341 MPa,抗拉强度由353 MPa提高至404 MPa。在拉伸过程中,因SiC_P与基体界面脱黏导致裂纹优先在SiC_P/AZ91层内萌生和扩展,AZ91层对微裂纹扩展具有一定的阻碍作用。