Effect of quenching cooling rate on residual stress and microstructure evolution of 6061 aluminum alloy

In this study,the cooling rate was manipulated by quenching with water of different temperatures(30,60 and 100℃).Surface and internal residual stresses in the quenched 6061 aluminum alloy samples were measured using hole-drilling and crack compliance methods,respectively.Then,the processability of the quenched samples was evaluated at cryogenic temperatures.The mechanical properties of the as-aged samples were assessed,and microstructure evolution was analyzed.The surface residual stresses of samples W30℃,W60℃and W100℃is−178.7,−161.7 and−117.2 MPa,respectively along x-direction,respectively;and−191.2,−172.1 and−126.2 MPa,respectively along y-direction.The sample quenched in boiling water displaying the lowest residual stress(~34%and~60%reduction in the surface and core).The generation and distribution of quenching residual stress could be attributed to the lattice distortion gradient.Desirable plasticity was also exhibited in the samples with relatively low quenching cooling rates at cryogenic temperatures.The strengthes of the as-aged samples are 291.2 to 270.1 MPa as the quenching water temperature increase from 30℃to 100℃.Fine and homogeneous β"phases were observed in the as-aged sample quenched with boiling water due to the clusters and Guinier-Preston zones(GP zones)premature precipitated during quenching process.

Silicon Mitigates Aluminum Toxicity of Tartary Buckwheat by Regulating Antioxidant Systems

Aluminum (Al) toxicity is a considerable factor limiting crop yield and biomass in acidic soil. Tartary buckwheatgrowing in acidic soil may suffer from Al poisoning. Here, we investigated the influence of Al stress on the growthof tartary buckwheat seedling roots, and the alleviation of Al stress by silicon (Si), as has been demonstrated inmany crops. Under Al stress, root growth (total root length, primary root length, root tips, root surface area, androot volume) was significantly inhibited, and Al and malondialdehyde (MDA) accumulated in the root tips. At thesame time, catalase (CAT) and ascorbate peroxidase activities, polyphenols, flavonoids, and 1,1-diphenyl-2-picrylhydrazyl(DPPH) and 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) free-radical scavenging abilitywere significantly decreased. After the application of Si, root growth, Al accumulation, and oxidative damage wereimproved. Compared to Al-treated seedlings, the contents of ·O2− and MDA decreased by 29.39% and 25.22%,respectively. This was associated with Si-induced increases in peroxidase and CAT enzyme activity, flavonoidcompounds, and free-radical scavenging (DPPH and ABTS). The application of Si therefore has positive effectson Al toxicity in tartary buckwheat roots by reducing Al accumulation in the roots and maintaining oxidationhomeostasis.

Effect of Sc on Al_(3)Fe phase and mechanical properties of as-cast AA5052 aluminum alloy

The AA5052 aluminum alloy is widely used in automobile and aerospace manufacturing,and with the development of light-weight alloys,it is required that these materials exhibit better mechanical properties.Previous studies have demonstrated that the addition of Sc to aluminum alloys can improve both the microstructure and properties of the alloys.In this study,the effect of Sc on the Fe-rich phase and properties of the AA5052 aluminum alloy was studied by adding 0%,0.05%,0.2%,and 0.3%Sc.The results show that with the increase of Sc,the coarse needle-like Fe-rich phase gradually transforms into Chinese-script and then nearly spherical particles,reduce the size of Fe-rich phase,and refine the grain with increase of high angle grain boundaries(HAGBs).These microstructure changes enhance the strength of the AA5052 alloy through Sc addition.The ductility of the alloy is obviously improved because the addition of a lower amount of Sc changes the morphology of Fe-rich phase from needle-like into a Chinese-script,and it is subsequently reduced as a result of significant increase in HAGBs with increasing Sc content.

Effect of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy

The effects of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy extruded bar were investigated through various analyses,including electrical conductivity,mechanical properties,local corrosion properties,and slow strain rate tensile stress corrosion tests.Microstructure characterization techniques such as metallographic microscopy,scanning electron microscopy(SEM),and transmission electron microscopy(TEM)were also employed.The results indicate that the tensile strength of the alloy produced by T6I6 aging is similar to that produced by T6I4 aging,and it even exceeds 700 MPa.Furthermore,the yield strength increases by 52.7 MPa,reaching 654.8 MPa after T6I6 aging treatment.The maximum depths of intergranular corrosion(IGC)and exfoliation corrosion(EXCO)decrease from 116.3 and 468.5μm to 89.5 and 324.3μm,respectively.The stress corrosion factor also decreases from 2.1%to 1.6%.These findings suggest that the alloy treated with T6I6 aging exhibits both high strength and excellent stress corrosion cracking resistance.Similarly,when the alloy is treated with T6I4,T6I6 and T6I7 aging,the sizes of grain boundary precipitates(GBPs)are found to be 5.2,18.4,and 32.8 nm,respectively.The sizes of matrix precipitates are 4.8,5.7 and 15.7 nm,respectively.The atomic fractions of Zn in GBPs are 9.92 at.%,8.23 at.%and 6.87 at.%,respectively,while the atomic fractions of Mg are 12.66 at.%,8.43 at.%and 7.00 at.%,respectively.Additionally,the atomic fractions of Cu are 1.83 at.%,2.47 at.%and 3.41 at.%,respectively.

Microstructure and mechanical properties of stationary shoulder friction stir welding joint of 2A14-T62 aluminum alloy

2A14-T62 butt joint was successfully welded by stationary shoulder friction stir welding(SSFSW)method.The results showed that using a pin with small shoulder could broaden the process window,and under a rotation speed of 2000 r/min and welding speed of 30 mm/min,joint with smooth surface,small reduction in thickness and little inner defects was obtained.The weld nugget zone was approx-imately circular,which was a unique morphology for SSFSW.The heat-affected zone(HAZ)and thermo-mechanically affected zone(TMAZ)were both quite narrow due to the lower heat input and slight mechanical action of the stationary shoulder.The fraction of high angle grain boundaries(HAGBs)exhibited a“W”shape along horizontal direction(from advancing side to retreating side),and the minim-um value located at HAZ.The average ultimate tensile strength and elongation of the joint were 325 MPa and 4.5%,respectively,with the joint efficiency of 68.3%.The joint was ductile fractured and the fracture surface contained two types of dimples morphology in different re-gions of the joint.Microhardness distribution in the joint exhibited a“W”shape,and the difference along the thickness direction was negli-gible.The joint had strong stress corrosion cracking susceptibility,and the slow stain rate tensile strength was 139 MPa.Microcrack and Al2O3 particulates were observed at the fracture surface.

Residual stress with asymmetric spray quenching for thick aluminum alloy plates

Solution and quenching heat treatments are generally carried out in a roller hearth furnace for large-scale thick aluminum alloy plates.However,the asymmetric or uneven spray water flow rate is inevitable under industrial production conditions,which leads to an asymmetric residual stress distribution.The spray quenching treatment was conducted on self-designed spray equipment,and the residual stress along the thickness direction was measured by a layer removal method based on deflections.Under the asymmetric spray quenching condition,the subsurface stress of the high-flow rate surface was lower than that of the low-flow rate surface,and the difference between the two subsurface stresses increased with the increase in the difference in water flow rates.The subsurface stress underneath the surface with a water flow rate of 0.60 m^(3)/h was 15.38 MPa less than that of 0.15 m^(3)/h.The simulated residual stress by finite element(FE)method of the high heat transfer coefficient(HTC)surface was less than that of the low HTC surface,which is consistent with the experimental results.The FE model can be used to analyze the strain and stress evolution and predict the quenched stress magnitude and distribution.

Effect of heat treatment on stress corrosion cracking, fracture toughness and strength of 7085 aluminum alloy

The influences of heat treatment on stress corrosion cracking （SCC）, fracture toughness and strength of 7085 aluminum alloy were investigated by slow strain rate testing, Kahn tear testing combined with scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that the fracture toughness of T74 overaging is increased by 22.9% at the expense of 13.6% strength, and retrogression and reaging （RRA） enhances fracture toughness 14.2% without reducing the strength compared with T6 temper. The fracture toughness of dual-retrogression and reaging （DRRA） is equivalent to that of T74 with an increased strength of 14.6%. The SCC resistance increases in the order： T6〈RRA〈DRRA≈T74. The differences of fracture toughness and SCC were explained on the basis of the role of matrix precipitates and grain boundary orecioitates.

Effects of silicon content on microstructure and stress corrosion cracking resistance of 7050 aluminum alloy

Evolution of microstructure and stress corrosion cracking （SCC） susceptibility of 7050 aluminum alloy with 0.094%, 0.134% and 0.261% Si （mass fraction） in T7651 condition have been investigated. The results show that the area fraction of Mg2Si increases from 0.16% to 1,48% and the size becomes coarser, while the area fraction of the other coarse phases including Al2CuMg, Mg（Al,Cu,Zn）2 and A17Cu2Fe decreases from 2.42% to 0.78% with Si content increasing from 0.094% to 0.261%. The tensile strength and elongation of 7050-T7651 alloys is decreased with the increase of Si content by slow strain rate test （SSRT） in ambient air. However, electrical conductivity is improved and SCC susceptibility is reduced with the increase of Si content by SSRT in corrosion environment with 3.5% NaCl solution.

Simulation of temperature and stress in 6061 aluminum alloy during online quenching process

The cooling curves of 6061 aluminum alloy were acquired through water quenching experiment. The heat transfer coefficient was accurately calculated based on the cooling curves and the law of cooling. The online quenching process of complex cross-section profile was dynamically simulated by the ABAQUS software. The results suggest that the heat transfer coefficient changes during online quenching process. Different parts of the profile have different cooling velocity, and it was verified by water quenching experiment. The maximum residual stress of the profile was predicted using FEM simulation based on ABAQUS software The relations between the temperature and stress were presented by analyzing the data of key points.

Effect of flow stress—strain relation on forming limit of 5754O aluminum alloy

A modified Swift type flow stress—strain relation was presented in order to describe the uniaxial tension test curve reasonably. The FLD-strain （forming limit diagram made up of limit strain） of 5754O aluminum alloy sheet was calculated based on the two flow stress—strain relations using Yld2000-2d yield function. By comparing the theoretical and experimental results, it is found that the calculated FLD-strain based on the modified Swift flow stress—strain relation can reasonably describe the experimental results. However, though the common Voce flow stress—strain relation can describe the deformation behavior during homogenous deformation phase accurately, the FLD-strain calculated based on it is obviously lower than the experimental result. It is concluded that the higher the hardening rate of sheet metal is, the higher the forming limit is. A method for determining the reasonable flow stress—strain relation is recommended for describing the material behavior during inhomogenous phase and the forming limit of sheet metal.

Preliminary Study on the Adaptability of Cucumis hystrix Chakr. under Aluminum Salt Stress

[Objective] The study was carried out to research the adaptability of Cucumis hystrix Chakr.under aluminum salt stress.[Method] Using Cucumis hystrix Chakr.and three cultivated cucumbers as tested materials,the change of physiological indexes including POD activity,SOD activity,electrolyte leakage and the content of malondialdehyde（MDA）,proline（Pro）content and soluble sugar were studied.[Result] The POD activity,SOD activity,proline content and soluble sugar content of Cucumis hystrix were higher than these of cultivated cucumbers,while electrolyte leakage and MDA content were lower,and it showed that Cucumis hystrix had better adaptability under aluminum salt stress.[Conclusion] Our study could lay a foundation for the improvement of cultivated cucumber by using the excellent characteristics of Cucumis hystrix.

Prediction of vulnerable zones based on residual stress and microstructure in CMT welded aluminum alloy joint

Numerical simulation and experimental results were employed for the identification of the most vulnerable zones in three-pass cold-metal-transferring （CMT） welded joint. The residual stress distribution in the joint was predicted by finite element （FE） method, while the structural morphology of distinctive zones was obtained through metallographic experiments. The highest principal stress made the symmetric face of the joint most sensitive to tensile cracks under service conditions. Whereas, the boundaries between the weld seam and the base plates were sensitive to cracks because the equivalent von Mises stress was the highest when the first interpass cooling was finished. The third weld pass and the inter-pass remelted zones exhibited the modest mechanical performances as a result of the coarse grain and coarse grain boundary, respectively. The most vulnerable zones were regarded to be the crossed parts between the zones identified by numerical and experimental methods.

高强Al-Zn-Mg-Cu合金静态再结晶模型及组织演变

采用Gleeble 3800热模拟试验机对航空用Al-Zn-Mg-Cu合金的热变形行为进行了测试,对变形后的微观组织进行了表征,系统分析了静态软化行为,建立了静态再结晶动力学模型。结果表明:实验用航空Al-Zn-Mg-Cu合金的静态再结晶激活能为129162 J·mol^(-1),静态再结晶体积分数受变形温度、变形程度、变形速率的影响,且变形温度对静态再结晶影响最明显;变形速率一定时,变形温度越高,道次停留时间的影响越不明显;350℃低温变形后,α-Al基体晶粒内部仍存在大量的位错缠结;400℃中温变形后,位错运动能够充分进行,部分晶粒发生了再结晶;450℃高温变形后,基体晶粒基本全部完成了再结晶,基体晶粒内部发现5~25 nm尺寸范围的Al-Zn-Mg-Cu四元相粒子;对于不同热变形条件,模型预测值的误差在0.008~0.0625范围内,动力学模型的计算结果精确度较高。

Zr对Al-Si-Mg-Mn合金凝固过程、时效组织和性能的影响

通过模拟计算、组织观察以及力学性能测试,研究了不同Zr含量对铸造Al-Si-Mg-Mn合金凝固过程、时效组织及力学性能的影响。结果表明,随着Zr含量增加,合金凝固路径存在显著差异,晶粒由初期树枝晶逐步演变为等轴晶;175℃时效7 h条件下,Zr的加入显著提高合金硬度。Zr的加入促使析出相在更低时效温度析出,这可能是Zr细化了晶粒从而提高了扩散效率。峰值时效时合金主要析出相为β″相和Q′相。

自然时效对Al-6.5Zn-2.3Mg-2.2Cu合金厚板组织性能的影响

商用7×××系铝合金产品人工时效前一般会经历自然时效,自然时效时间的长短直接决定产品的生产制备流程。本试验研究了工业化制备的Al-6.5Zn-2.3Mg-2.2Cu合金厚板在不同的自然时效阶段经人工时效处理后的组织及性能,并重点分析了短时自然时效(0.125~21 d)及长时自然时效(30~360 d)对合金不同时效状态的影响。研究结果表明:自然时效0.125~21 d,T6态合金的强度持续降低,抗拉和屈服强度的降幅分别为14 MPa和17 MPa,伸长率在13.6%~15.6%的范围内波动;基体析出相主要为GPII区和η′相,晶界析出相呈断续分布。自然时效3~360 d时,T6态合金的强度、伸长率和断裂韧性均在一定范围内波动,无明显的变化规律,基体析出相主要为η′相且分布密集,晶界析出相呈断续分布。自然时效3~105 d时,T76态合金的拉伸性能和断裂韧性同样在一定范围内波动,无明显的变化规律,基体析出相尺寸粗大、分布分散,主要为η′相和η相,晶界析出相同样呈断续分布。

Fe、Ni元素微合金化对Al-11Si铝合金微观组织及力学性能的影响

本研究利用扫描电子显微镜(SEM)、能量散射X射线光谱(EDS)和拉伸试验机,研究了Ni(1.2及1.6wt.%)和Fe(0.6及0.8wt.%)含量对Al-11Si铝合金的微观组织及不同温度下的力学性能的影响。实验结果表明,适量的Ni元素对于Al-11Si合金中富含Fe相的类型、形态和分布具有积极作用。在Al-11Si铝合金中添加1.2wt.%Ni和0.6wt.%Fe可以生成一种类似“汉字状”的富Fe强化相。当进一步增加到1.6wt.%Ni和0.8wt.%Fe后,富Fe相变为了长针状,对Al基体产生严重的割裂作用,降低了合金力学性能。由于含有1.2wt.%Ni和0.6wt.%Fe的Al-11Si铝合金中生成了“汉字状”富Fe强化相,合金的高温拉伸性能得到了显著改善。在350℃的测试温度下,Al-11Si铝合金的抗拉强度(UTS)达到了139 MPa。

1060Al/Al-Al_(2)O_(3)/1060Al层状铝基复合材料热变形模型对比分析

采用Gleeble-3500热模拟试验机在变形温度为25~400℃、应变速率为0.01~10s^(-1)和真应变为0.85的条件下,对1060Al/Al-Al_(2)O_(3)/1060Al层状铝基复合材料进行了热压缩试验,研究其热变形行为,建立了应变补偿的Arrhenius (SCA)、修正的Johnson-Cook (MJC)和修正的Zerilli-Armstrong (MZA) 3种本构模型,并对流变应力的预测值与实验值进行对比。结果表明,层状复合材料流变应力呈加工硬化型,并随温度升高或应变速率降低而降低;在100℃/0.5s^(-1)、200℃/0.1s^(-1)和300℃/0.1s^(-1)条件下,层状复合材料组元层间变形较为协调;3种本构模型中,MZA模型的相关系数最高,R为0.99085、平均绝对相对误差最低,e_(AARE)为0.046966,更适合描述1060Al/Al-Al_(2)O_(3)/1060Al层状铝基复合材料的热变形行为。

Effect of pre-deformation on the stress corrosion cracking susceptibility of aluminum alloy 2519

The effects of pre-deformation and strain rate on the stress corrosion cracking （SCC） behavior of aluminum alloy 2519 in air and in 3.5% NaCI water solution were investigated by means of slow strain rate tension （SSRT）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results indicate that the alloy is susceptible to SCC in 3.5% NaCI water solution and not in air. At the same pre-deformation, the alloy is more susceptible to SCC at 1.33 × 10^-5 s^-1 than at 6.66 × 10^-5 s^-1. Moreover, it is more susceptible to SCC at free pre-deformation than at 10% pre-deformation at the same strain rate. The number of 0 precipitated along the grain boundaries is reduced and distributed discontinuously, at the same time, the precipitate-free zones （PFZ） become narrow and the susceptibility to stress corrosion cracking is reduced after 10% pre-deformation.

锌镁比对Al-Zn-Mg-Cu-Er-Sc-Zr合金显微组织与耐腐蚀性能影响的研究

通过调整Al-Zn-Mg-Cu-Er-Sc-Zr合金中的Mg元素含量,研究了Zn/Mg比的变化对合金相演变以及腐蚀性能的影响规律。结果表明:Al_(8)Cu_(4)Er相、Al_(3)(Er,Sc)相与含Fe相存在明显的伴生关系,二者依附于含Fe相生长。Zn/Mg比的变化可显著改变三者间的交互形式,高的Zn/Mg比例有利于稀土相独立生长,且在比值为4.18的条件下,Al_(8)Cu_(4)Er相与含Fe相均得到了显著细化。细化的晶界第二相使腐蚀坑深度仅为82μm,而连续的伴生混合相、粗大稀土相等均会不同程度降低合金的耐蚀性能。

Effect of quenching rate on microstructure and stress corrosion cracking of 7085 aluminum alloy

The influence of quenching rate on microstructure and stress corrosion cracking （SCC） of 7085 aluminum alloy was investigated by tensile test, slow strain rate test （SSRT）, combined with scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electrochemical test. The results show that with decreasing the quenching rate, the size and inter-particle distance of the grain boundary precipitates as well as precipitation free zone width increase, but the copper content of grain boundary precipitates decreases. The SCC resistance of the samples increases first and then decreases, which is attributed to the copper content, size and distribution of grain boundary precipitates.