Pit-to-crack transition in pre-corroded 7075-T6 aluminum alloy under cyclic loading

Pit-to-crack transition experiments were conducted on 1.600 mm and 4.064 mm 7075-T6 aluminum alloy. Specimens were corroded using a 15:1 ratio of 3.5% NaCl solution and H₂O₂ prior to fatigue loading. Cracks originating from corrosion pits were visually investigated in order to understand how pit-to-crack transitions occur.All prior corroded specimens in the study fractured from cracks associated with pitting. Pit-to-crack transition was successfully acquired visually. Corroded 7075-T6-4.064 mm specimens experienced more of an overall fatigue life reduction than 7075-T6-1.600 mm specimens. Results indicated that quantities such as pit surface area and surrounding pit proximity are as important as pit depth in determining when and where a crack will form.     

不同热处理状态的2219铝合金动态加载下力学行为和断裂机制研究

本文通过分离式霍普金森拉杆实验,研究了不同热处理状态的2219铝合金在动态加载下的力学行为和断裂机制。结果表明：2219-T6和2219-T4的抗拉强度和应变率敏感性随着应变率的增加而增加,而2219-O的则先增加后减小,且2219铝合金的应变率敏感性和应变硬化率随着应变的增加而减小;在动态加载下,材料在较高的应力集中程度下形成了局部的解理及第二相颗粒碎裂的形貌,且在较高应变率(≥650 s-1)下,随着应变率的增加,应力集中程度更高,解理形貌的占比也越大,同时由于材料在裂纹扩展的同时依旧可以发生一定量的变形,使得材料整体在较高应变率(≥650 s-1)下具有更高的成形极限,也导致材料在较高的加工硬化下形成具有低塑性特征的断口。     

Damage mechanisms in the particle reinforced aluminum alloy 6061 under creep loading

The creep behaviour of the particle reinforced aluminium alloy 6061 is investigated using experimental and numerical techniques. In order to describe the influence of ceramic particles on the overall creep curve of the composite an idealised unit cell model with a periodic arrangement of particles is generated. The particles are assumed to react linear elastically. Particle cleavage is taken into account. For the matrix an additive viscosity hardening law coupled with an isotropic damage variable is used. The results show that the fracture time is strongly influenced by the presence of particles. Qualitative good agreement with experimental data is found.     

Textures variation of 3104 aluminum alloy sheets under different rolling conditions

1　INTRODUCTIONLargequantityoftheAl Mn Mgalloy 310 4isusedinthemanufactureofaluminumbeverage .Muchattentionwaspaidtothecontroloftextureandearinginthedeepdrawingstagesofmanufacture .Thetex tureinthecanstockwasextensivelyinvestigated .Oneearingofaluminumalloyisverycloserelatedtothetexture ,agoodassociationofthetexturescompo nentsearingdropsobviously ,inthissituationthe 4 foldearingat 0°/90°andearingat± 4 5°occursto gether[15] .Theappearanceof 4 foldearingat 0°/90°isduetothecubetext…     

Behavior of 316L stainless steel containing corrosion pits under cyclic loading

The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits.     

多轴载荷下ZL101铝合金的低周疲劳行为

研究不同等效应变幅下ZL101铝合金在多轴比例和非比例载荷下的低周疲劳行为,并用透射电镜观察合金的疲劳行为中的位错结构。结果表明：合金在两种加载方式下均表现为循环硬化;在非比例载荷下合金表现出附加强化,但程度不明显;合金的疲劳寿命随等效应变幅的增加而降低,合金在非比例加载下的疲劳寿命低于比例加载时的疲劳寿命。对位错结构的观察表明,随等效应变幅度的提高,合金的低周疲劳位错结构从交叉位错带转化为位错胞,合金在非比例加载下更易形成位错胞结构。     

Environment sensitive cracking of a nickelaluminium bronze under monotonic and cyclic loading conditions

It has been demonstrated that a cast nickelaluminium bronze is susceptible to environment sensitive cracking in natural seawater over a restricted range of potentials in the vicinity of the free corrosion potential. The cracking shows structural sensitivity, being particularly likely to initiate and follow the interfaces of α?κ₁ regions, and is also strain rate sensitive. In monotonic strain rate tests the threshold stress for cracking decreases from the UTS at a strain rate of about 10^?8 s^?1 to about 60% of the 0.2% proof stress at a strain rate of about 10^?6 s^?1. Cyclic loading at various relatively low frequencies (below 10 Hz) also promotes cracking only above a threshold of about 60% of the 0.2% proof stress. There is some evidence that dwell times interposed between periods of changing stress raise the thresholds somewhat towards the 0.2% proof stress. Crack velocities above the thresholds are in the range 10^?7 to 10^?6 mm s^?1, depending upon stressing conditions, although higher crack velocities obtain as stresses rise at faster strain rates to approach conditions for mechanical separation. The effects of strain rate and the observed crack velocities are consistent with a crack growth mechanism that is essentially dissolution controlled.     

Al-Mg-Si系铝合金不同变形条件下的组织力学行为

对6014铝合金进行了常温拉深试验,采用不同的拉深凸模速度,研究了该铝合金变形中的组织力学行为;对6016铝合金进行热拉伸试验,相同应变速率下采用不同的拉伸温度,研究了该铝合金在热拉伸过程中的组织力学行为。实验表明:随着凸模速度(10~30 mm·min~(-1))增加,6014铝合金的常温拉深深度增大;随着拉伸温度(400~550℃)升高,6016铝合金的硬度增大,且沿拉伸轴向硬度值波动越大;在应变速率为1 s~(-1)、温度为500℃下热拉伸,变形区有明显的动态再结晶过程,进一步升高温度会造成再结晶组织的晶粒粗化;6014和6016铝合金中均存在大量的Al、Fe、Si结晶相,但原始组织中6016的析出相更弥散,尺寸大小更均匀,更集中分布于晶界附近;比较6014铝合金常温拉深组织和6016铝合金热拉伸组织,冷变形后的晶粒组织更均匀,热拉伸后的晶粒尺寸差异很大,会降低材料变形后的力学性能。     

铝合金板在循环塑性变形下的韧性断裂行为模拟(英文)

基于数值模拟的方法研究在循环塑性变形下铝合金板的力学行为。首先,通过Cockcroft-Latham韧性断裂准则得到材料的断裂极限应力图,并通过实验对成形极限应力图进行验证。数值模拟结果表明:滚边时弯曲中心的应变路径可以认为是平面应变状态;采用绳式滚边方法可以改善在弯曲中心线上的应力集中现象。从滚边断口的扫描电镜照片可以发现,循环塑性变形对铝合金板的韧性断裂行为有影响。     

6XXX铝合金防撞梁总成在动静态载荷下的变形行为

针对6XXX铝合金防撞梁总成,采用准静态拉伸实验、200 s~(-1)动态拉伸实验获得材料的应力-应变曲线,通过数值模拟得到6063-T6和6082-T6合金材料的Swift-Hockett-Sherby硬化模型参数,对6XXX铝合金防撞梁总成的三点静压和13 km·h~(-1)台车碰撞进行数值模拟和实验验证。结果表明:应变速率变化范围为0. 001～200 s~(-1)时,6063-T6合金应变率敏感性不明显,6082-T6合金表现出明显的应变率敏感性;基于拉伸试验和数值模拟得到的Swift-Hockett-Sherby硬化模型参数能较精确地表征铝合金的塑性行为;三点静压的支反力-位移曲线和低速碰撞的加速度-时间曲线以及变形行为与仿真预测结果吻合度较高,该方法能够准确地预测6XXX铝合金防撞梁总成在动静态载荷下的变形行为。     

Vibration behavior of a precipitation-hardening aluminum alloy under resonance

The shearable coherent precipitates and precipitation free zones of the Al–Mg–Si alloy with respect to different aging conditions resulted in localization of strain on persistant slip planes and grain boundaries respectively. And these inhomogeneous deformation related to the precipitation behavior significantly affected the vibration properties of the Al–Mg–Si alloy, including damping capacity and deflection amplitude under resonance.     

Ductile fracture behavior of 5052 aluminum alloy sheet under cyclic plastic deformation at room temperature

Ductile fracture behavior of a 5052 aluminum alloy sheet undergoing cyclic plastic deformation is investigated in order to clarify the effect of cyclic plastic deformation on formability enhancement in incremental stretch sheet forming at room temperature. In the incremental forming, formability markedly increases owing to strain distribution and accumulation effects. The former effect is activated when the deformation region expands along tool paths. Thus, localization of deformation, which leads to necking or fracturing, can be prevented. On the other hand, local strain is accumulated without fracturing when a blank sheet is repeatedly subjected to out-of-plane deformation at the same position. In this paper, the effect of the strain accumulation due to cyclic deformation generated by bending and unbending is primarily focused on to discuss the effect on deformability. To apply cyclic plastic straining to the specimen, a cyclic stretch-bending test was adopted. A cyclic tensile test was also conducted for larger bending curvature. The experimental results show that cyclic bending–unbending affects the ductility of sheet metals. The fractography obtained by scanning electric microscopy also indicates that fewer and smaller voids are observed particularly on bending the inner side than on the outer side.     

Superplasticity of hydrogen-containing VT6 titanium alloy with a submicrocrystalline structure

Concentration and temperature regimes of hydrogen treatment have been found, which in combination with severe plastic deformation allow one to obtain a microstructure with a size of constituents of about 0.1 μm in the VT6 titanium alloy. It has been shown that the alloy with such a structure has superplastic properties in a temperature range from 500 to 650°C. Characteristics of superplasticity of a hydrogenated submicrocrystalline VT6 alloy and a basic alloy, in which the submicrocrystalline structure was obtained without hydrogen alloying, have been compared. Particular features of a hydrogenated submicrocrystalline VT6 alloy in a superplastic state are considered.