Effect of three-step homogenization on microstructure and properties of 7N01 aluminum alloys

The effect of different homogenization treatments on the microstructure and properties of the 7N01 aluminum alloy was investigated using hardness measurements, electrical conductivity measurements, tensile and slow strain rate tests, electron probe microanalysis, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results revealed that three-step homogenization improved the uniformity of Zr distribution by eliminating segregation of the main alloying elements. During the second homogenization step at 350 °C for 10 h, coarse and strip-like equilibrium η phases formed which assisted the nucleation of Al3Zr dispersoids and reduced the width of the precipitate-free zone of A13Zr dispersoids. As a result, coarse recrystallization was greatly reduced after homogenization at 200 °C, 2 h ＋ 350 °C, 10 h ＋ 470 °C, 12 h, which contributed to improving the overall properties of the 7N01 aluminum alloys.

Evolution of residual stress field in 6N01 aluminum alloy friction stir welding joint

Based on the characteristics of friction stir welding( FSW) and Coulomb friction work theory,the residual stresses field of FSW joints of 6 N01 aluminum alloy( T5),which was used in high speed train,were calculated by using the ANSYS finite element software. During the FEM calculation,the dual heat source models namely the body heat source and surface heat source were used to explore the evolution law of the welding process to the residual stress field. The method of ultrasonic residual stress detecting was used to investigate the residual stresses field of the 6 N01 aluminum alloy FSW joints. The results show that the steady-state temperature of 6 N01 aluminum alloy during FSW is about 550 ℃,and the temperature mutates at the beginning and at end of welding. The longitudinal residual stress σ_x is the main stress,which fluctuates in the range of-25 to 242 MPa. Moreover,the stress in the range of shaft shoulder is tensile stress that the maximum tensile stress is 242 MPa,and the stress in the outside of shaft shoulder is compressive stress that the maximum compressive stress is 25 MPa. The distribution of the tensile stress in the welding nugget zone( WNZ) is obviously bimodal,and the residual stress on the advancing side is higher than that on the retreating side. With the increasing of the welding speed,the maximum temperature decreased and the maximum residual stress decreased when the pin-wheel speed kept constant. With the increasing of the pin-wheel speed,the maximum temperature of the joint increased and the maximum residual stress increased when the welding speed was constant. The experimental results were in good agreement with the finite element results.

Dynamic experimental studies of a6n01s-t5 aluminum alloy material and structure for high-speed train

In this study, we focus on the dynamic failure property of A6N01S-T5 aluminum alloyusing for high-speed train. The method of SHBT+3D DIC was put forward to figure out the dynamic mechanical properties and dynamic failure strain of A6N01S-T5 aluminum alloy,and on the basis of this, Johnson-Cook model constitutive parameters and dynamic failure strain parameters were obtained through a series of static and dynamic tests.An important character of this methodwas that the sandwich structure from the true high-speed train was used in penetration test,followed by the numerical calculation of the same working condition using LS-DYNA.Then we compare the experimental results with simulation results mentioned above in terms of failure morphology in structure and the bullet speed throughout the entire process to verifythe accuracyof the parameter. The experimental results provide a data basis for the crash simulation model of high-speed trains,in turn to optimize the structural design and whole efficiency.

Damage and fracture mechanism of 6063 aluminum alloy under three kinds of stress states

To study the damage and fracture mechanism of 6063 aluminum alloy under different stress states,three kinds of representative triaxial stress states have been adopted,namely smooth tensile,notch tensile,and pure shear.The results of the study indicate the following.During the notch tensile test,a relatively higher stress triaxiality appears in the root of the notch.With the applied loading increasing,the volume fraction of microvoids in the root of the notch increases continuously.When it reaches the critical volume fraction of microvoids,the specimen fractures.During the pure shear test,the stress triaxiality almost equals to zero,and there is almost no microvoids but a shear band at the center of the butterfly specimen.The shear band results from nonuniform deformation constantly under the shear stress.With stress concentration,cracks are produced within the shear band and are later coalesced.When the equivalent plastic strain reaches the critical value（equivalent plastic fracture strain）,the butterfly specimen fractures.During the smooth tensile test,the stress triaxiality in the gauge of the specimen remains constant at 0.33.Thus,the volume of microvoids of the smooth tensile test is less than that of the notch tensile test and the smooth specimen fractures due to shearing between microvoids.The G-T-N damage model and Johnson-Cook model are used to simulate the notch tensile and shear test,respectively.The simulated engineering stress-strain curves fit the measured engineering stress-strain curves very well.In addition,the empirical damage evolution equation for the notch specimen is obtained from the experimental data and FEM simulations.

Deformation and damage mechanism of aluminum alloy under different stress states

The deformation and damage mechanism of aluminum alloy (6063) were investigated by 0°, 30°, 45°, 60°and 90°tensile tests and tensile-unload tests with the modified Arcan fixture on the butterfly specimens. The results show: the curves of engineering stress-engineering strain under different stress states are obviously different. There were microvoids in the specimen when 0°direction loading was preformed. The microcracks were produced in the root of notch as the result of the microvoids shearing fracture and then they led to specimen fracture with microcracks being coalesced. With tensile angle increasing, the shear stress in the center of butterfly specimen increases gradually, while the deformation bands become more and more concentrative. In these concentrative deformation bands, the microcracks are produced and then microcracks propagation and coalescence result in specimen fracture. When 90°direction loading is preformed, the shear bands are obviously formed. The G-T-N damage model and the Johnson-cook model were used to simulate 0°tensile test and 90°tensile test respectively. The simulated engineering stress-engineering strain curves fit the measured ones very well.

Effects of in-situZrB_2 nanoparticles and scandium on microstructure and mechanical property of 7N01 aluminum alloy

In this study, the in-situ synthesized ZrB_(2) nanoparticles and rare earth Sc were introduced to enhance the strength and ductility of 7N01 aluminum alloy, via the generation of high-melting and uniform nanodispersoids. The microstructure and mechanical property evolution of the prepared composites and the interaction between ZrB_(2) and Sc were studied in detail. The microstructure investigation shows that the introduction of rare earth scandium(Sc) can promote the distribution of ZrB_(2) nanoparticles, by improving their wettability to the Al melt. Meanwhile, the addition of rare earth Sc also modifies the coarse Al Zn Mg Mn Fe precipitated phases, refines the matrix grains and generates high-melting Al_3(Sc,Zr)/Al_3Sc nanodispersoids. Tensile tests of the composites show that with the combinatorial introduction of ZrB_(2) and Sc, the strength and ductility of the composites are improved simultaneously compared with the corresponding 7N01 alloy, ZrB_(2) /7N01 composite and Sc/7N01 alloy. And the optimum contents of ZrB_(2) and Sc are 3 wt% and 0.2 wt% in this study. The yield strength, ultimate strength and elongation of(3 wt% ZrB_(2) +0.2 wt% Sc)/7N01 composite are 477 MPa, 506 MPa and 9.8%, increased about 18.1%, 12.2%and 38% compared to 7N01 alloy. Furthermore, the cooperation strengthening mechanisms of ZrB_(2) and Sc are also discussed.

SNOEK-Kê-K■STER PEAK OF INTERNAL FRICTION IN Fe-P-N ALLOYS

The internal friction and precipitate phases of the deformed Fe-P-N alloys have been investigated. It has been found that the ratio of depends on the content of P and the relation holds if the content of N is lower than 30wt.ppm and the content of P is lower than 640wt.ppm. It shows that the intercept K2 is related to the presence of the atomic pairs and clusters of P in the alloy matrix.

EFFECT OF La ON SNOEK-KE-K■STER PEAK IN Fe-P-N ALLOYS

The effect of La addition in Fe-P-N upon Snoek-Ke-Kster(SKK)damping peak was studied.It was found that the damping depends on the atomic concentration ratio between La and P(C_(La)/C_P).When the ratio is comparatively high in the alloy(for example,4.56 on 2.6),La will appreciably enhance SKK damping,whereas in the alloy saturated with P at a lower C_(La)/C_P ratio of 0.27 La will no longer exert any effect on SKK peak.

Phase Transition and Band Structure Tuned by Strains in Al_(1/2)Ga_(1/2)N Alloy of Complex Structure

Phase transition and band structure tuned by uniaxial and biaxial strains are systematically investigated based on the density-functional theory for ordered All/2 Ga1/2N alloys of complex structures. Although the structural transformations to graphite-like from wurtzite are energetically favorable for both types of strain, the phase transitions are different in nature： the second-order transition induced by uniaxial strain is jointly driven by the mechanical and dynamical instabilities and the first-order transition by biaxial strain only by the mechanical instability. The wurtzite phase always shows the direct band gap, while the band gap of the graphite-like phase is always indirect. Furthermore, the band gaps of the wurtzite phase can be reduced by both types of strain, while that of the graphite-like phase is enhanced by uniaxial strain and is suppressed by biaxial strain.

Tuning interface mechanism of FeCo alloy embedded N,S-codoped carbon substrate for rechargeable Zn-air battery

The interface mechanism between catalyst and carbon substrate has been the focus of research.In this paper,the FeCo alloy embedded N,S co-doped carbon substrate bifunctional catalyst(FeCo/S-NC)is obtained by a simple one-step pyrolysis strategy.The experimental results and density functional theory(DFT)calculation show that the formation of FeCo alloy is conducive to promoting electron transfer,and the introduction of S atom can enhance the interaction between FeCo alloy and carbon substrate,thus inhibiting the migration and agglomeration of particles on the surface of carbon material.The FeCo/SNC catalysts show outstanding performance for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).FeCo/S-NC shows a high half-wave potential(E_(1/2)=0.8823 V)for ORR and a low overpotential at 10 mA cm^(-2)(E_(j=10)=299 mV)for OER.In addition,compared with Pt/C+RuO_(2) assembled Zn-air battery(ZAB),the FeCo/S-NC assembled ZAB exhibits a larger power density(198.8 mW cm^(-2)),a higher specific capacity(786.1 mA h g_(zn)~(-1)),and ultra-stable cycle performance.These results confirm that the optimized composition and the interfacial interaction between catalyst and carbon substrate synergistically enhance the electrochemical performance.

Effect of long-term thermal exposure on microstructure of laser-welded UNS N10003 alloy

The evolution of the microstructure and tensile rupture mechanism of laser welds in UNS N10003 alloy exposed to 700℃are investigated.Fine M_(6)C carbides precipitate around the primary eutectic M_(6)C-carbides in the fusion zone after 100 h of exposure.During long-term thermal exposure,the size of the fine M_(6)C carbides increased.The eutectic M_(6)C-carbides in the as-welded fusion zone transformed into spherical M_(6)C carbides as the exposure time extends to 10000 h.Additionally,the spherical M_(6)C particles exhibit size coarsening with increasing exposure time.The tensile properties of the welded joints are not adversely affected by the evolution of eutectic M_(6)C-carbides and the coarsening of M_(6)C carbides.

淬回火工艺对N-Mo合金化Cr13型耐蚀塑料模具钢组织与力学性能的影响

对N-Mo合金化Cr13型耐蚀塑料模具钢进行925~1150℃保温0.5 h的油淬处理,再分别进行150~300℃保温2 h或者350~600℃保温1 h的回火处理,研究了淬回火工艺对该钢组织与力学性能的影响。结果表明:试验钢淬火后的组织主要为淬火马氏体,随着淬火温度的升高,晶粒长大,第二相逐渐固溶进基体,试验钢的硬度先增大后降低,当淬火温度为1050℃时,硬度达到峰值,为57.7 HRC,此时第二相基本固溶进基体,残余奥氏体体积分数仅为8.49%。随着回火温度的升高,试验钢组织由回火马氏体向索氏体转变,第二相逐渐析出并长大;硬度呈先降低后升高再迅速降低的趋势,冲击吸收能量随回火温度的变化规律与回火硬度的变化规律相反,抗拉强度的变化规律与硬度的变化规律一致,屈服强度呈先增大后降低的趋势,并在回火温度为480℃时达到最大值,为1445 MPa;在200℃以上温度回火后试验钢的塑性均保持在一个较好的水平。试验钢获得优异综合性能的热处理工艺为1050℃×0.5 h淬火+200~300℃×2 h回火,此时组织为回火马氏体,硬度为48~53 HRC,抗拉强度为1752~2050 MPa,屈服强度为1171~1223 MPa,冲击吸收能量为41~51 J,断面收缩率为42%~51%,断后伸长率为17.1%~17.7%。

Fatigue behavior and life prediction of A7N01 aluminium alloy welded joint

Fatigue characteristics of A7N01 aluminium alloy welded joint were investigated and a fatigue crack initiation life-based model was proposed. The difference of fatigue crack initiation life among base metal, weld metal and heat affected zone (HAZ) is slight. Furthermore, the ratio of fatigue crack initiation life (Ni) to fatigue life to failure(Nf) is a material dependent parameter, 26.32%, 40.21% and 60.67% for base metal, HAZ and weld metal, respectively. Total fatigue life predicted using the presented model is in good agreement with the experimental data and that using Basquin’s model. The observation results of fatigue fracture surfaces, using scanning electron microscope (SEM), demonstrate that fatigue crack initiates from smooth surface due to welding process for weld metal, blowhole in HAZ causes fatigue crack initiation, and the crushed second phase particles play an important part in fatigue crack initiation in base metal.

V-N微合金化热轧因瓦合金的组织和性能

因瓦合金具有极低的热膨胀系数,但较低的力学强度严重制约其在结构材料领域的应用。为进一步提升因瓦合金的强度,借鉴微合金化思想,设计了V-N微合金化因瓦合金。采用维氏硬度计、拉伸试验机、电子背散射衍射(EBSD)、X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)等研究了微量V、N对热轧因瓦合金显微组织和力学性能的影响,并分析其作用机理。结果表明:V-N微合金化因瓦合金的热轧组织显著细化,硬度和抗拉强度显著增加;随着N含量增加,其晶粒尺寸进一步细化,且分布更为均匀,抗拉强度进一步增加。V-N微合金化因瓦合金的基体上析出了大量细小、弥散分布的V(C,N)第二相,尺寸约为400 nm,其钉扎晶界和位错。细晶强化、析出强化和位错强化是V-N微合金化因瓦合金力学性能显著提升的主要原因。

缺口对34CrNi3Mo合金钢的扭转疲劳性能的影响

以船舶主轴为实验对象,研究34CrNi3Mo合金钢作为船舶主轴时法兰与主轴连接处的疲劳寿命.利用实验将法兰与主轴连接处简化成带U型缺口的扭转疲劳试样,基于小样本量中值S-N实验法对应力集中系数为1.45的34CrNi3Mo合金钢在扭转荷载作用下进行疲劳分析,测定其在不同应力幅值下的疲劳寿命并绘制S-N曲线,估算其疲劳极限.将绘制出的S-N曲线与光滑试样的S-N曲线进行对比,结果发现疲劳寿命差别较大.利用ABAQUS软件和Fe-safe软件进行数值模拟,将试验结果与所绘的S-N曲线对比表明,S-N曲线的方程与试验结果很接近,验证了所建立的数值模型的正确性.

高熵合金/陶瓷在Ti(C,N)基金属陶瓷中的研究现状与展望

Ti(C,N)基金属陶瓷因其具有良好的硬度、耐磨性和化学稳定性,成为制造业中不可或缺的关键材料,进一步提高金属陶瓷材料的强韧性对扩大其应用领域和应用规模具有十分重要的意义。本文阐述了Ti(C,N)基金属陶瓷的相结构特点,并重点综述了高熵合金/陶瓷在Ti(C,N)基金属陶瓷的黏结相和添加相成分设计和制备中的应用。对高熵合金/陶瓷在金属陶瓷的主要研究方向进行了总结展望:在Ti(C,N)基金属陶瓷中加入高熵合金黏结相后组织的演变和对材料性能的影响机理需进一步研究;同时高熵陶瓷添加相在Ti(C,N)基金属陶瓷中的作用及机理也是一个重要的研究方向。

Heterostructure design of Fe^(3)N alloy/porous carbon nanosheet composites for efficient microwave attenuation

The self-dissipation and attenuation capacity of materials play an important role in realizing efficient electromagnetic absorption,in this case,the roles of macroscopic composition and micro-structure should be emphasized simultaneously in the reasonable design of microwave absorbent.Given that,Fe_(3)N alloy embedded in two-dimensional porous carbon composites were fabricated via facile sol-gel and sacrificial template methods.Satisfactorily,the magnetic/dielectric materials combination and porous structure introduction are conductive to the optimization of impedance matching property,as result of the enhancement of microwave absorption capacity.In addition,sufficient magnetic loss capacity,strong conductivity as well as polarization attenuation bring about the outstanding microwave absorbing performance with an effective absorption bandwidth of 6.76 GHz and a minimum reflection loss value of-65.6 d B.It is believed that this work not only lay a foundation to achieve microwave response materials in a wide frequency range,but also emphasize the significant role of the component selection and structural design.

Structural and magnetic properties of Sm_2Fe_(17-x)Nb_x (x = 0-4) alloys prepared by HDDR processes and their nitrides

Sm2Fe17-xNbx （x = 0-4） powder was synthesized by HDDR treatment and nitrogenation. The effects of partial Nb substitution for Fe on the structural and magnetic properties of Sm2Fe17-xNbx alloys and their nitlides were investigated. It was seen that Sm2（Fe,Nb）17 phase exists in both annealed and HDDR-treated Sm2Fe17-xNbx alloys. However, its content is decreased with the increase in Nb substitution. In annealed alloys, Sm2（Fe,Nb）17 phase becomes unstable and will dissociate into SmFe2 and Fe-rich phases when x 〉 1.5. With HDDR-treatment, the Nb concentration in recombined Sm2（Fe,Nb）17 phase is decreased, and the content of Fe-rich phases is increased. Sm2Fe17-xNbx powder exhibits dendritic cracks and fine particles with a size of less than 300 nm. In nitrogenated alloys, N atoms mainly enter 2：17-type phase to form Sm2（Fe,Nb）17Ny. Partial Nb atoms in Sm2（Fe,Nb）17Ny phase will be released or excluded by nitrogen atoms. Fe-rich phases increase, and are followed by the amorphous Sm2（Fe,Nb）17Ny phase. Nb substitution for Fe with x = 0.5 and 1.0 in Sm2Fe17-xNbxNy powders increases the coercivity and remanence. But when x is greater than 2.0, Nb substitution will deteriorate the magnetic properties.

Rapid synthesis of Ti(C,N) powders by mechanical alloying and subsequent arc discharging

Ti（C,N） powders were synthesized by mechanical alloying （MA） from a mixture of pure titanium and graphite under a nitrogen atmosphere in a planetary mill.Effects of arc discharging on phase transformation and microstructure of MA powders milled for 1-7 h were explored.The results show that Ti（C,N） powders were prepared after mechanical milling for 1 h and subsequent arc discharge treatment,whereas the synthesis reaction did not occur in 7 h by mechanical milling alone.The ions produced during arc discharging interacted with powder particles and accelerated the diffusion of atoms and the nucleation on the surface of the as-milled powder,which results in fast synthesis of Ti（C,N） powders.The formation mechanisms of the two synthesis processes are self-propagating reactive synthesis.

Deformation resistance of Fe-Mn-V-N alloy under different deformation processes

The deformation resistance of Fe-Mn-V-N alloy under different deformation conditions was investigated by hot compression method on thermal simulator. Effects of deformation degree, deformation temperature, and strain rate on deformation resistance were analyzed. The results show that when other conditions are constant, the deformation resistance increases with the increase in deformation degree and strain rate and decreases with the increase in deformation temperature. At the same time, the mathematical model of deformation resistance for Fe-Mn- V-N alloy was established by lstOpt software using the Levenberg-Marquardt optimization algorithm carried out on the fitting of regression coefficients, which has higher fitting precision.