LY12合金粗晶材料的超塑性变形机制

采用单轴拉伸对LYl2粗晶材料进行超塑性研究，温度一定时，在较高和较低的应变速率下都得到了大延伸率，而处于中间应变速率的试样延伸率较低。SEM断口分析表明，晶界上产生的粘性物质对粗晶超塑性行为有决定性影响。在高应变速率下，晶界上粘性层很薄，被粘性层包围着的晶粒和亚结构在相互挤压和相对转动中容易细化，有利于超塑性变形能力的提高且不易产生孔洞，室温性能良好；低应变速率下，大多晶界上都有粘性物质包围且粘性层厚度增大，粘性物质的增多使超塑性变形能力增强，但易产生孔洞，使室温性能恶化；而中间应变速率区间，晶粒细化程度不够，晶界上末产生较多粘性物质，有少量孔洞产生且变形能力较差。     

预热处理对铝合金LY12超塑性变形的影响

本文探讨了预备热处理对铝合金LY12超塑性变形的影响.得出CZ供应状态的铝合金LY12不需采用通常的超塑性预备热处理工艺,在最佳超塑性成形温度430℃保温4 h,以最佳应变速率ε=1.67×10-4S-1变形,可获得超塑性延伸率452%.     

供应态LC9铝合金的超塑性试验研究

通过拉伸实验研究了供应态LC9铝合金经退火处理后的超塑性变形特性.在初始应变速率3.3×10-4 s-1,拉伸温度410～510℃时,合金均具有超塑性,平均伸长率为106%～181%.最佳超塑性温度为450℃,最佳初始应变速率为3.3×10-4 s-1,在此温度和应变速率条件下,合金平均伸长率达到181%,m值为0.41,流动应力仅为14.4MPa.显微组织和断口观察表明,在超塑性变形过程中发生了明显的动态再结晶,再结晶晶粒等轴、细小、均匀.空洞在晶界处形核、长大,最后连接,导致试样断裂.     

供应态LC9铝合金的超塑性试验研究

通过拉伸实验研究了供应态LC9铝合金经退火处理后的超塑性变形特性。在初始应变速率3.3×10-4s-1,拉伸温度410～510℃时,合金均具有超塑性,平均伸长率为106%～181%。最佳超塑性温度为450℃,最佳初始应变速率为3.3×10-4s-1,在此温度和应变速率条件下,合金平均伸长率达到181%,m值为0.41,流动应力仅为14.4MPa。显微组织和断口观察表明,在超塑性变形过程中发生了明显的动态再结晶,再结晶晶粒等轴、细小、均匀。空洞在晶界处形核、长大,最后连接,导致试样断裂。     

供应态2B70铝合金超塑性试验研究

试验研究了供应态2B70铝合金经普通退火处理后在不同变形工艺下的超塑性变化规律.结果表明:采用3.3×10-4 s-1的初始应变速率,在360℃～490℃的拉伸温度范围内2B70铝合金具有一定的超塑性.450℃为合金的最佳超塑性拉伸温度,3.3×10-4 s-1为最佳初始应变速率,在最佳超塑性条件下合金的最大伸长率达到193.3%,流动应力为13.94 MPa.在超塑性拉伸过程中,由于不断发生动态回复及再结晶,晶粒趋于明显细化和等轴化.合金的超塑性变形是以晶界滑移为主的变形机制,在较低拉伸温度及较高初始应变速率下晶界滑移痕迹较少,表现出明显的晶间断裂特征.     

供应态LY12CZ铝合金在超塑性形变中晶界形态的研究

采用光学显微镜、扫描电镜和透射电镜对未经任何预处理、晶粒尺寸为19μm～21μm之间的供应态LYl2CZ铝合金超塑性形变中晶界形态进行了观察、分析。结果表明，此状态下的铝合金在超塑性变形过程中晶界宽度和形态会发生改变。在较大伸长率的条件下，晶界出现宽边化和圆弧化。在超塑性变形过程中形成的宽边晶界属于介稳状态的界面，在高温下短时间保温，宽边晶界会发生晶化，变成细小的普通晶界。试样在超塑性变形时产生的伸长率与晶界宽度有密切联系。在此次试验中超塑性伸长率大的试样其晶界宽度在2．1μm～2．7μm之间。     

AZ31B镁合金板材超塑性变形与断裂机理研究

研究了工业态热轧AZ31B镁合金板材的超塑性及其变形机制,在应变温度为723K,应变速率为1×10-3s-1的试验条件下,其最大断裂伸长率达到216%,应变速率敏感性指数达0.36。研究结果表明:晶界滑动(GBS)是工业态热轧AZ31B镁合金超塑性的主要变形机制,变形初期有动态再结晶发生,断裂是由晶界处形成的空洞不断长大、连接而引起的。     

粗晶铝合金超塑性变形机理的研究现状

介绍了国内外粗晶铝合金超塑性的基本研究情况。对粗晶铝合金超塑性变形机理的研究进行归类总结，主要包括：扩散蠕变机理、伴随扩散蠕变的晶界滑移机理、位错蠕变/滑移机理、液相协调机理、动态再结晶机理、晶粒群滑移机理和空洞连接协调机制。并针对低成本发展铝合金超塑性研究的迫切性，展望了粗晶材料的应用前景。指出了除大晶粒外，高应变速率和低温条件下的超塑性也是目前铝合金变形研究的方向。     

Al-5.3Cu-0.8Mg-0.6Ag铝合金板的高温超塑性研究

研究了Al-5.3Cu-0.8Mg-0.6Ag合金板在温度400℃~520℃以及应变速率1×10-4s-1~1×10-1s-1下的超塑性变形能力及其变形机制。结果显示,轧制态的Al-5.3Cu-0.8Mg-0.6Ag合金在500℃及应变速率5×10-4s-1时的最大延伸率为320%,应变速率敏感系数达到0.58。高应变速率下超塑性变形过程中主要机制为晶界滑动,协调机制则是空洞的形核长大与断裂。     

LY12CZ铝合金超塑性应变速率变化规律探讨

在挂锤式拉伸试验机上对LY12CZ铝合金超塑性应变速率变化规律进行了跟踪观察。发现试验在恒载荷下以最初应变速率变形的时间只有40～60min。随后,应变速率会自动增大,试样断裂时的应变速率比较初始应变速率约高1倍。     

Cavity growth in a superplastic Al–Mg alloy: II. An improved plasticity based model

The extent of cavity growth estimated from a combination of diffusional and plasticity based growth models generally underestimates the actual cavity growth in superplastic alloys. It has been shown that in a fine grain Al–Mg alloy, cavity growth begins by matrix/particle debonding at grain boundary particles (Mat. Sci. Forum, Trans. Tech. Pub. 304–306 (1999) 609), and also from pre-existing voids. In this study, cavity growth beyond interface decohesion is modeled in which deformation of the matrix surrounding the cavity is free from interface constraint, but it still experiences an accelerated local deformation rate. Stress and strain-rate in this region are intensified due to the perturbed flow field near the cavity, and not relaxed during the time frame for superplastic forming. This local deformation around the cavity is a function of strain-rate sensitivity, m, the level of strain concentration, and the cavity spacing. Two important effects not previously considered: (i) local stress concentration around the cavities, and (ii) continuous nucleation of new cavities, have been included in this work. Using this model that is suitable for low overall cavity volume (i.e. no cavity coalescence), faster growth rate is predicted for single cavities when strain-rate sensitivity is low and/or the population density of cavities is low (generally at slow strain-rates). By combining the predicted growth rate of individual cavities with the emerging cavity population density determined experimentally, a quantitative understanding of the various complex dependencies of cavitation has been obtained.     

Superplastic deformation of 15 vol% SiCp/LY12 aluminum composite under an electric field

In this paper, influence of an external electric field on mechanical performance of deformation, cavity formation, and fracture mechanisms has been investigated during superplastic deformation of 15 vol% SiC_p/LY12 (LY12 matrix corresponds approximately to ASTM 2024) aluminum composite. The experimental results show that the appropriate electric field makes the strain-rate sensitivity index increase and the superplasticity improve. The results obtained by scanning electron microscopy (SEM) show that the nucleation growth and linkage or coalescence of cavities is restrained by applying an external electric field; meanwhile, fracture transforms from intergranular tear to typical superplastic failure, that is, fracture by formation and coalescence of cavities at particles and boundaries.     

Limited Effect of Twin Boundaries on Radiation Damage

The different influences of the general grain boundary and the twin boundary on the cavity formation were investigated in copper irradiated by helium at room temperature.Large number of the cavities with sizes smaller than 5 nm formed after irradiation,which were almost homogenously distributed inside the grains.However,the distribution of the cavities varied near the general grain boundary and the twin boundary.Cavities-depleted zone was readily observed near the general grain boundaries,which was rarely observed near the twin boundaries.Meanwhile,decoration of dense cavities within the grain boundary plane was observed.The results suggested the limited influence of the twin boundaries as the point defect sinks compared with the general grain boundaries.     

Effect of current pulses on fracture morphology in superplastic deformation of 2091 Al Li alloy

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钛镁合金的汽相淬火工艺

在总结超塑变形二维晶粒重排模型基础上，研究了超塑变形三维晶粒重排。金相观察表明：１号铝锂合金板状试样宽度方向边层微细晶粒填入了中心层大晶粒在拉伸方向产生的空洞而实现晶粒重排。通过扫描电镜观察了晶粒涌出及２号名锂合金中大Ａｌ３Ｚｒ相在变形时的转动情况。研究表明，微细晶粒是通过晶粒转动填入空洞的，该过程是一个能量降低的过程。宽度方向微细晶粒的运动解释了超塑变形的试样宽度尺寸的减小及试样板边缘局部颈缩迁     

Ti-6Al-4V合金超塑性变形时的组织演化

利用光学显微镜和扫描电镜对超塑性拉伸后的细晶Ti-6Al-4V合金分别进行了断口形貌分析和组织演化规律研究。结果表明:细晶Ti-6Al-4V合金室温拉伸时,断裂方式为准解理断裂;超塑性拉伸时,试样断裂的主要形式是韧窝-空洞聚集型断裂。在初始应变速率不变的条件下,随着拉伸温度的升高,α相晶粒尺寸增大,β相数量增多,空洞数量减少,且在840℃至930℃拉伸时,α相晶粒仍保持等轴状态,但在较高温度(960℃)拉伸时,α相晶粒被拉长,部分区域出现网篮组织。在拉伸温度不变时,随着初始应变速率的降低,α相晶粒尺寸增大,β相增多,空洞数量减少。高温(960℃以上)拉伸时,β相颗粒具有良好的塑性和较低的硬度,丰富的β相有利于晶界协调滑动,并对空洞的产生具有抑制作用。     

Superplastic deformation of duralumin LY12CZ under an electric field

The general superplastic deformation of many alloys had been studied exhaustively. Recently, the superplastic deformation of some alloys has been achieved by the application of an electric field to the process. Conrad and his colleagues have obtained the change of the flow stress and the strain-rate exponent during the superplastic deformation of 7475 Al alloy subjected to an external dc electric field. However, it is not clear how the electric field will affect the elongation and the growth of cavities quantitatively, and whether the type of cavities will change because of the existence of the external electric field.

In this paper, the optimum process parameters for the super plastic deformation of duralumin LY12CZ, without any pre-treatment, subjected to an external dc electric field have been obtained, LY12CZ (corresponding to ASTM 2024) being used widely in the aeronautic-astronautic industry. Furthermore, the effect of the electric field on the superplasticity and the superplastic-deformation conditions has been investigated. The experimental results show that the application of the electric field: (i) decreases the flow stress by 10–25% and the degree of cavitation at the onset of the fracture by 11% approximately; (ii) reduces the rate of strain-hardening; and (iii) increases the strain-rate sensitivity exponent by 26–38%. It is important to note that: (iv) the elongation of the superplastic deformation of LY12CZ under the electric field increases by 14–45% as compared with that without the electric field; (v) the equivalent strain at the onset of the rapid growth of the cavities increases by 25% with the application of the electric field; and (vi) spherical cavities exist in the specimens after the tensile test when applying the electric field, as opposed to the V-type cavities for the general superplastic deformation of LY12CZ. From these investigations, the optimum process parameters for the superplastic deformation of LY12CZ under an electric field are as follows: the deformation temperature is 471°C and the initial strain rate is 0.333 × 10⁻³ s⁻¹.     

THE SUPERPLASTICITY AND DEFORMATION MECHANISM OF ULTRALIGHT BINARY Mg-8wt%Li ALLOY

1.IntroductionMagnesium--lithiumalloysarethelightestalloysamongthenonpoisonousmetalsandalloystll.Becauseoftheirlowdellsityandhighspecificstiffness,theyhavethepotentialforuseinaerospacesarmoredvehicle,automobileandelectricindustry.InordertoturnMg--Lialloysintospecificcomponentswithminimumamountofmachiningandjoining,itisdesirablethatMg-Lialloysexhibitsuperplasticity.UPtonow,superfinegraillscanbeobtainedinmagnesium-lithiumalloysbythefollowingways'(1)staticannealingafterthermomechanicaltreatment…     

A COMPLEX DEFORMATION MECHANISM FOR SUPERPLASTIC DEFORMATION OF Mg ALLOY

本文选用大晶粒和微细晶粒两种镁合金,利用现代测试手段进行超塑性变形机制的研究.结果表明,在超塑性变形条件下,两种合金都显示以晶界滑动为主的,由扩散蠕变和位错滑移所协调的复合变形机制.作者提出一个包括三种变形机制在内的复合机制模型.在超塑性变形中,下层金属晶粒通过晶界滑动不断涌现到试样表面横向晶界发生宽化及空洞的地方,从而不断增加沿拉伸轴方向上的晶粒数.这是试样在拉伸变形中获得非常大的伸长量的原因.