ECAP变形对MWCNTs/AZ31复合材料抗腐蚀性能的影响

采用碳纳米管孕育块铸造法制备多壁碳纳米管/AZ31镁基复合材料,经等径角挤压(ECAP)变形后对复合材料在3.5%NaCl(质量分数)的腐蚀介质中进行静态浸渍试验和电化学极化曲线测定,研究等径角挤压变形工艺对复合材料抗腐蚀性能的影响;利用数码相机、扫描电子显微镜对复合材料腐蚀前后的表面形貌进行观察和分析;并对复合材料的抗腐蚀机理进行分析。结果表明:等径角挤压变形工艺能有效的提高多壁碳纳米管(CNTs)/AZ31复合材料的抗腐蚀性能,经等径角挤压变形4道次后,复合材料的平均腐蚀速率由挤压态的0.6035mg/(m2·s)降为0.2963mg/(m2·s)。腐蚀电流密度Icorr由ECAP变形前的3.363μA/cm2减小到2.269μA/cm2。     

ECAP对碳纳米管/AZ31复合材料显微组织的影响

采用碳纳米管孕育块铸造法制备了碳纳米管/AZ31镁基复合材料,并对其进行了等径角挤压实验.利用光学金相显微镜对它的显微组织进行了观察和分析,研究了等径角挤压变形工艺对复合材料显微组织的影响规律.结果表明:等径角挤压工艺可明显细化复合材料的晶粒组织;随着变形道次的增加,复合材料平均晶粒尺寸不断得到细化,组织更加均匀.     

AZ31镁合金挤压轧制过程微观织构演变

利用光学显微分析和电子背散射衍射(Electron Back Scatter Diffraction,简称EBSD)技术,研究了AZ31镁合金在挤压开坯、轧制及退火过程中微观组织和织构的演变规律。结果表明:挤压后板材呈现出特殊的纤维织构,基面平行于挤压方向,在随后的轧制过程中纤维织构逐渐向基面织构转化,且随变形量的增加,基面织构逐渐增强,最终形成了强烈的基面板织构。     

特殊成形工艺下AZ31镁合金的织构及变形机制

通过组织观察以及宏观和微观织构测定、分析了异步轧制及等径角轧制的AZ31镁合金形变机制,确定了在这两种工艺下{0001}基面织构的改善效果.结果表明:异步轧制产牛的平行于轧面的剪切力促进了与普通轧制状态下相反的基面滑移,使基面织构连续地弱化为倾转的基面织构;而等径角轧制通过产生与轧向成122.5°的剪切力,使基面取向的晶粒产生拉伸孪晶,形成与基面织构共存的柱面织构.因此这两种特殊工艺都可能改善镁合金的塑性.还分析了形变量和退火对织构的影响.     

热轧过程中AZ31镁合金的组织及织构演变

对AZ31镁合金铸轧板进行单道次热轧实验,利用光学显微镜、X射线和透射电镜对热轧过程中微观组织和织构的演变规律进行研究。结果表明:AZ31镁合金铸轧板具有较强的基面织构,当热轧变形量较小时,孪生是主要的变形机制;当热轧变形量较大时,位错滑移成为主要的变形机制;10%热轧态中出现的透镜状的{1012}宽孪晶使基面织构明显减弱;20%热轧过程中则出现{1012}、{1011}-{1012}两种不同形貌的孪晶;当变形量大于20%时,位错滑移大量开动,基面织构也显著增强,并在随后的退火过程形成细小均匀的再结晶组织。     

基于变形均匀性的AZ31镁合金ECAP多道次成形工艺研究

以AZ31镁合金为研究对象,利用刚塑性有限元法,研究ECAP变形工艺条件对变形均匀性的影响.模拟得到的试样主要变形区的平均等效应变值与理论等效应变值吻合度高.结果表明:变形均匀性改善主要集中在前4道次,而后4道次变化不大;过高或低的坯料温度均不利于应变的均匀分布;适当的摩擦系数和较低的挤压速度能促进试样均匀变形.结合正交实验,得出控制变形均匀性的最优方案是:模具温度240℃,坯料温度270℃,摩擦系数0.3,挤压速度3mm· s-1.     

AZ31镁合金的织构对其力学性能的影响

利用电子背散射衍射(EBSD)取向成像技术,分析AZ31镁合金热挤压棒材和轧制薄板的织构特点;对具有不同初始织构的镁合金棒材和薄板进行力学性能分析,并从织构角度分析棒材的拉压不对称性和薄板的力学各向异性。结果表明:挤压镁合金棒材具有主要以(0001)基面平行于挤压方向的基面纤维织构,存在严重的拉压不对称性,其原因在于压缩时的主要变形方式为{1012}1011孪生;热轧镁合金薄板具有主要以(0001)基面平行于轧面的强板织构,具有显著的力学性能各向异性,其原因在于拉伸时不同方向的基面滑移Schmid因子不同。     

基于变形均匀性的AZ31镁合金ECAP多道次成形工艺研究

以AZ31镁合金为研究对象,利用刚塑性有限元法,研究ECAP变形工艺条件对变形均匀性的影响。模拟得到的试样主要变形区的平均等效应变值与理论等效应变值吻合度高。结果表明:变形均匀性改善主要集中在前4道次,而后4道次变化不大;过高或低的坯料温度均不利于应变的均匀分布;适当的摩擦系数和较低的挤压速度能促进试样均匀变形。结合正交实验,得出控制变形均匀性的最优方案是:模具温度240℃,坯料温度270℃,摩擦系数0.3,挤压速度3mm.s-1。     

温热弯曲成形过程中AZ31镁合金型材的微观织构演变

采用光学显微镜、X射线衍射仪和EBSD分析研究AZ31镁合金型材温热弯曲成形前后横截面外侧微观组织和织构的演变规律。结果表明:弯曲成形前,型材为(10 10)平行于挤压方向的线织构;弯曲成形后,型材线织构被削弱。弯曲过程中拉伸孪晶数量减少,由弯曲前的5.39%降低至弯曲后的2.22%;压缩孪晶增多,由弯曲前的0.141%增加至弯曲后的0.222%。挤压型材的大量拉伸孪晶使得应力集中,协同温度的影响,非基面滑移开动并协调了晶粒c轴的应变,因而提高型材的塑性变形能力。     

挤压态AZ31镁合金拉伸变形织构分析

根据X射线衍射图谱绘制了晶面反极图,研究了拉伸变形对挤压态AZ31镁合金织构的影响.结果表明,挤压态AZ31镁合金具有明显的(0002)基面织构,且存在C轴与挤压方向呈16°～21°角分布的倾斜基面织构.拉伸变形使基面织构弱化,(1010)柱面沿C轴发生了45°角的转动.     

WMCNTs/AZ31复合材料电化学腐蚀研究

采用碳纳米管孕育块铸造法制备碳纳米管/AZ31镁基复合材料,测量其电化学极化曲线,研究碳纳米管加入量对复合材料抗腐蚀性能的影响,利用SEM对复合材料腐蚀前后的表面形貌进行了观察和分析。结果表明,碳纳米管的加入有效地提高了复合材料的抗腐蚀性能,随着复合材料中碳纳米管加入量的增加,腐蚀电流密度I_corr由5.279 μA/cm²减小到2.994 μA/cm²。     

Texture evolution of extruded AZ31 magnesium alloy sheets

The evolution of texture during the annealing and hot rolling process of extruded AZ31 magnesium alloy sheets was studied. There are two kinds of texture components in the extruded AZ31 sheets. One is {0002}<1-010> and the other is {1-010}<1-120>. The {0002}<1-010>component predominates. After annealing at 723 K for 3 h, both {0002}<1-010> and {1-010}<1-120> components are strengthened moderately. This indicates that grains with both two components mentioned above grow faster than those with other orientations. The {1-010}<1-120> component disappears and the intensity of {0002}<1-010> component decreases significantly after hot rolling with a 30% reduction at 623 K. This is mainly attributed to rotational dynamic recrystallization (RDX) during the hot rolling.     

Texture evolution by shear on two planes during ECAP of a high-strength aluminum alloy

The evolution of texture was examined during equal-channel angular pressing (ECAP) of an Al–Zn–Mg–Cu alloy having a strong initial texture. An analysis of the local texture using electron backscatter diffraction demonstrates that shear occurs on two shear planes: the main shear plane (MSP) equivalent to the simple shear plane, and a secondary shear plane which is perpendicular to the MSP. Throughout most regions of the ECAP billet, the MSP is close to the intersection plane of the two channels but with a small (5°) deviation. Only the {1 1 1}〈1 1 0〉 and {0 0 1}〈1 1 0〉 shear systems were activated and there was no experimental evidence for the existence of other shear systems. In a small region at the bottom edge of the billet that passed through the zone of intersection of the channels, the observed textures were fully consistent with the rolling textures of Copper and Goss.     

Microstructure and texture evolution of AZ31 magnesium alloy during rolling

The production of magnesium alloy sheets normally involves several processing stages including hot rolling,cold rolling and intermediate annealing.The microstructure and texture evolution of AZ31 magnesium alloy sheets in different processing states were investigated by optical microscopy and X-ray diffraction technique.It is found that the microstructure of hot-rolled sheets is dominated by recrystallized equiaxed grains,while that of cold-rolled sheets is dominated by deformation twins.With final annea...