模具温度对Si_p/ZA27复合材料组织及性能的影响

研究了模具温度对触变成形Sip/ZA27复合材料组织及力学性能的影响。结果表明,随着模具温度升高,锭料的凝固速率变慢,初生α-Al颗粒尺寸和体积分数增大;而且初生α-Al颗粒中Zn元素的含量增加;此外,Si颗粒的团聚倾向变得严重。通过对试样的力学性能进行比较可知,最佳的模具温度为200℃,此时的抗拉强度和伸长率分别达到382 MPa和1.17%。而且随着模具温度的增加,断裂机制发生转变。     

原位自生Sip/ZA27复合材料的磨损性能

研究Sip体积分数和实验温度对原位自生Sip/ZA27复合材料磨损性能的影响。结果表明：随着Sip体积分数的增加,其耐磨性呈先增大、后减小、进而又增大的趋势;随着实验温度的升高,复合材料的耐磨性减弱,但不同Sip体积分数的材料其耐磨性减小的幅度不同;所有这些变化均由磨损机理决定;随Sip体积分数的增加,材料的主导磨损机制将从较严重的磨损机制——塑性变形诱导磨损和粘着磨损转向轻微的磨损机制——涂抹磨损,进而又转向严重的磨损机制——塑性变形诱导磨损,最后则又转变为相对轻微的磨损机制——伴随磨料磨损的涂抹;随着实验温度的升高,主导磨损机制从轻微的磨损机制——伴随磨料磨损的涂抹转向严重的磨损机制——塑性变形诱导磨损和粘着磨损;高硬度磨层的形成与否决定着Sip/ZA27复合材料的耐磨性及磨损机制。     

Al-25％Si合金过热处理后的凝固行为和组织研究

研究了熔体过热温度、冷却速度及浇注温度对Al-25％Si合金凝固形核温度、初生硅尺寸和数量分布的影响.结果显示,过热温度增加、冷却速度增大均会影响初生硅形核温度.随过热温度升高,形核温度增加,直至1 000℃过热后形核温度降低.增加冷却速度使形核温度进一步升高.不同冷却速度下,初生硅相尺寸和数量随过热温度增加以相同规律变化,1 000℃时尺寸细化达到最小值,数量达到最大值.冷却速度对初生硅尺寸的影响与过热温度有关,低过热温度下,增加冷却速度有利于初生硅相尺寸细化,过热温度升高,冷却速度对尺寸的影响逐渐减小.熔体过热处理对初生硅相的影响还与浇注温度有关,降低浇注温度,初生硅尺寸粗化,同时硅颗粒数量减少.Al-25％Si合金熔体高温过热处理后在850℃浇注,能够将初生硅相尺寸细化至30μm以下.     

原位反应法TiB_2/ZA27复合材料的组织及性能研究

采用原位反应法制备出不同颗粒含量的TiB_2/ZA27复合材料,研究了TiB_2颗粒含量对TiB_2/ZA27复合材料组织及性能的影响。结果表明,TiB_2/ZA27复合材料主要由α-Al相、η-Zn相、ε-CuZn_4相和TiB_2粒子组成,不存在明显的Al_3Ti和AlB_2相;原位生成的TiB_2颗粒对α-Al相产生明显的细化效果,为η-Zn相提供了更多的形核基底,使其晶粒细化、数量增加,在基体中的分布形态改变。随TiB_2颗粒含量的增加,α-Al相和η-Zn相的尺寸减小,α+η共析组织数量增加,材料的强度和硬度得到显著提高。     

原位生成TiB2/ZA27复合材料的组织与耐摩擦磨损性能

以铝熔体为载体,采用混合盐反应法生成形状规则、尺寸细小的TiB2颗粒,再传递到ZA27合金中,获得TiB2/ZA27复合材料。通过金相显微镜、XRD、SEM、EDS和摩擦磨损试验等分析方法测试了复合材料的微观组织和耐摩擦磨损性能。结果显示,TiB2颗粒在TiB2/ZA27复合材料中分布均匀,平均直径小于3μm。TiB2颗粒的加入对基体组织有显著的细化效果,并随着TiB2颗粒含量的增加,复合材料的耐摩擦磨损性能相比于基体材料有明显提高。     

热等静压制备Si_p/Al-Cu复合材料的组织与性能

采用热等静压(HIP)技术制备50Sip/Al-Cu和70Sip/Al-Cu复合材料(50Sip/Al-4.0Cu和70Sip/Al-4.0Cu,Si含量为体积分数,Cu的质量分数为4.0%),利用XRD和扫描电镜研究热等静压态样品的相组成和组织形貌,并测试其主要物理和力学性能。结果表明:材料完全致密、Si颗粒在Al基体中分布均匀且组织细小;热等静压态的50Sip/Al-Cu和70Sip/Al-Cu复合材料的热膨胀系数分别为12.7×10 6和8.7×10 6K 1,抗弯强度分别为395和350MPa,热处理后的材料强度拉弯可进一步提高至548和397 MPa,与采用其他技术制备的同类材料相比,热等静压制备的Sip/Al-Cu复合材料在保持低膨胀系数的同时具有更高的抗弯强度及其他力学性能。     

浇注温度和压射速度对Al-30Si压铸组织和力学性能的影响

研究液态压铸过程中浇注温度和压射速度对Al-30Si压铸组织和力学性能的影响.结果表明,随着浇注温度的升高,Al-30Si压铸组织中的初生硅尺寸在不断减小.温度从780℃升高到820℃时,初生硅的尺寸出现了大幅度的减小,温度再升高则变化不明显;同时,抗拉强度随温度的变化也表现出同样的趋势.而压射速度对Al-30Si液态压铸组织的影响要比浇注温度的影响小得多.初生硅的尺寸随压射速度的增加有减小的趋势,但减小的幅度不大.当压射速度为8m/s时,压铸组织出现了明显的气孔、缩孔等缺陷.随着压射速度的增加,其抗拉强度呈现出了先增大后减小的趋势,最大值217N/mm2出现在压射速度为4m/s时.     

Sip/ZA27复合材料的晶粒细化工艺的研究

本文研究了Zr、RE对Sip/ZA27复合材料的晶粒细化工艺,结果表明:添加适当含量的Zr或RE时,都能使复合材料的晶粒得到一定程度的细化,Zr的晶粒细化能力强于RE,而只有Zr和RE复合添加才能得到细小的等轴晶组织,在添加0.2%Zr+0.8%RE时晶粒尺寸最小,达到60μm左右。     

近液相线铸造法对高硅铝合金组织与性能的影响

为获得性能优良的高硅铝合金材料,采用近液相线铸造法制备高硅铝合金坯料,并对坯料显微组织进行金相观察;采用M256-60428金相检验软件计算晶粒尺寸及其圆整度,研究浇注温度对高硅铝合金初生α(Al)相尺寸形貌和力学性能的影响,并采用JSM6490/LV扫描电镜扫描压缩试样断口。结果表明,随着浇注温度的降低,铝合金显微组织呈现由树枝晶向蔷薇状形态、再到球状或粒状组织变化;而后,随着合金熔体处于半固态区间时间的延长,铝合金中的初生α(Al)又开始出现合并长大,圆整度有了明显的改善。随着浇注温度的降低,试样的硬度值也在减小,且减小的梯度不断增大。试样在720℃温度下浇注的抗压强度约为620MPa,得到的高硅铝合金试样在压缩时发生解理断裂;而在605℃温度下浇注的抗压强度则为505MPa,浇注后试样发生了混合断裂。     

RE对Sip/ZA27复合材料凝固组织的影响

研究了RE对Sip/ZA27复合材料的铸态、固溶态及半固态组织的影响,分析了随RE含量的变化复合材料组织形态的变化及RE的分布变化情况,并探究了RE对组织的影响机理.结果表明,随着RE含量的增加,晶粒形态由发达的羽毛状晶逐渐转变为等轴晶形态,晶粒尺寸呈减小趋势,在0.8％RE时晶粒尺寸最小；过量的RE与其他元素形成长针状的复杂化合物,使得细化作用减弱.     

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。