流变压铸成形镁合金AZ91D的显微组织与性能

采用双螺杆机械搅拌法制备半固态镁合金浆料,对比研究了液态压铸与半固态流变压铸成形镁合金AZ91D的组织与性能,探讨了半固态成形镁合金铸件的热处理强化机制.试验结果表明,流变压铸成形铸件与液态压铸成形铸件在铸态时的力学性能相当;由于半固态成形减轻了铸件内部气孔、偏析等铸造缺陷,因而T4和T6热处理均明显地提高了半固态成形镁合金铸件的力学性能.研究还得出,液态压铸成形镁合金铸件经过固溶处理之后,其抗拉强度和伸长率也有所提高,但是,时效处理明显地恶化了铸件的力学性能.     

ZL201铝合金半固态流变压铸组织与性能

研究了ZL201铝合金半固态流变压铸组织与性能,包括半固态浆料的制备、压铸成形和固溶、时效处理。结果表明:在ZL201铝合金液相线温度附近施加交变电磁场,能够获得均匀、细小、近球形非枝晶组织的半固态浆料;半固态浆料经压铸成形后,零件具有等轴或蔷薇状晶粒组织;经T5热处理后,ZL201铝合金的抗拉强度为253N/mm2,伸长率为7%。流变压铸件的组织和性能优于半固态触变压铸件的。     

AZ91D镁合金成形组织的研究

研究了AZ91D镁合金液态金属型、液态砂型、液态压铸成形、半固态流变压铸成形及其T6热处理后的组织特点。结果表明，半固态流变压铸成形组织中初生α相细小、圆整、分布较均匀，平均粒径为35-50μm，消除了其它成形组织中的树枝晶结构，同时生产验证该组织具有很好的薄壁件充填成形性能。     

支架零件半固态触变压铸成形工艺研究

研究了支架零件半固态触变压铸成形工艺,包括半固态坯料的制备、二次加热和压铸成形等.结果表明:采用低频电磁搅拌半连续铸造工艺制备半固态坯料,当电磁场频率为30 Hz时,能够获得均匀、细小的非枝晶组织;采用高温二次加热工艺,当坯料温度为640℃时,可获得适合半固态触变成形的均匀、近球形组织;半固态浆料以0.1 m/s低速通过内浇口,在充型20％进行1m/s高速切换后,能够获得充型完整、轮廓清晰、内部组织致密的半固态压铸成形件.     

ZL201合金半固态层流压铸成形过程数值模拟

采用Any Casting铸造仿真软件模拟研究了ZL201合金半固态触变压铸成形过程、成形后的组织及性能,并与实际铸件进行了比较。结果表明:ZL201合金半固态触变压铸成形在浆料温度600℃、模具温度240℃时,低速压射速度0.1 m/s,且在1.5 s后进行速度切换,高速压射速度为1 m/s时,所得铸件平均晶粒尺寸为72.56μm。铸件的平均硬度为HV 70.8,平均抗拉强度为212.5 MPa。     

铝合金半固态加工技术的应用研究

重点介绍了近年来在铝合金半固态坯料制备方面的研究进展以及在半固态触变成形技术工业应用方面的研究开发工作,如复合电磁搅拌制备半固态浆料、多流电磁搅拌半固态连铸技术、铝合金半固态触变压铸成形、铝合金半固态触变模锻成形等,并就其可能的应用领域及发展状况如难铸造合金的铸造成形、变形合金的直接铸造成形、活塞合金的加工成形、变形铝合金的塑性加工进行了讨论。     

镁合金半固态成型技术的进展

介绍了金属半固态成形技术的原理、分类及工艺特点，主要介绍了镁合金的半固态射铸成形、流变成形设备及其工作原理，对镁合金半固态成形技术与压铸成形工艺进行对比分析，并介绍了常用半固态铸造镁合金的力学性能；简要介绍了镁合金半固态成形技术的数值仿真模拟技术的进展，指出镁合金的半固态射铸法将成为生产镁合金铸件的主流技术。     

工艺参数对半固态流变压铸Al-Si-Mg合金组织与性能的影响

采用半固态流变压铸成形技术研制出Al-Si-Mg铝合金前舱，通过正交法对试验方案进行设计，研究了压射速度(0.2～0.3 m/s)、浇注温度(575～615℃)和压力(240～280 MPa)对铸件平均晶粒尺寸、平均形状因子、力学性能的影响，分析了Al-Si-Mg合金半固态浆料在流变压铸成形过程中的枝晶破碎和晶粒生长特征，讨论了组织与力学性能之间的内在联系及合金强化机理。结果表明，在试验条件下，各工艺参数对铸件组织和力学性能影响的重要性顺序依次为压射速度>浇注温度>压力；随着压射速度升高，浇注温度降低及压力升高，组织中的晶粒趋于细小圆整，屈服强度、抗拉强度和伸长率逐渐提高。优化工艺是压射速度为0.3 m/s,浇注温度为575℃,压力为280 MPa。     

镁合金半固态流变压铸型腔流动过程数值模拟的研究

利用数值模拟技术,模拟了镁合金液态压铸和半固态流变压铸成形充型流动过程.结果表明:半固态流变压铸成形在不同的内浇口尺寸与位置条件下都可以获得平稳的充型流动场,其工艺参数设计灵活;同等条件下,半固态流变压铸成形的型腔充填过程平稳,成形铸件的质量优于液态压铸成形.模拟结果与实验结果比较分析,两者的流动特征基本吻合.     

铝合金液态与半固态压铸件的组织性能研究

对A356铝合金液态与半固态压铸成形件在压铸态和T6热处理态下的力学性能与微观组织进行了研究。试验得出，与液态压铸成形件相比，半固态压铸成形件可以获得更佳的综合力学性能；经同样T6热处理后，两者抗拉强度都得到提高，伸长率下降，但半固态压铸成形件抗拉强度提高的幅度更大，伸长率降低得更少。从微观角度解释了两种不同成形方法产生这一性能差异的内在原因。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。