热处理对喷射沉积Al-27%Si合金显微组织及力学性能的影响

采用喷射沉积和热挤压致密化相结合的方法制备Al-27%Si合金,研究热处理对合金的组织及性能的影响。利用金相显微镜、扫描电镜和MTS-858型疲劳试验机等手段对Al-27%Si合金喷射沉积挤压态和热处理态的显微组织和力学性能进行观察与测试。结果表明:喷射沉积Al-27%Si合金组织细小均匀,初晶Si均匀弥散地分布在连续Al基体中,无针状共晶硅存在;采用合理的热挤压致密化工艺可以显著消除材料中的孔隙,致密度达到99.5%;热处理能够进一步改善材料的组织,但会降低材料的屈服强度。     

循环热处理对喷射沉积Al-27%Si合金组织和性能的影响

采用喷射沉积技术制备Al-27%Si(质量分数)合金,研究循环热处理对其组织、残余应力和力学性能的影响。采用Ansys有限元模拟结合X射线检测评估Al-27%Si合金残余热应力的分布和大小。结果表明,喷射沉积Al-27%Si合金由均匀细小的初晶Si和α-Al基体组成,初晶Si的尺寸随热循环温度升高和次数增加而增大。Ansys有限元模拟结果显示喷射沉积Al-27%Si合金增强体Si颗粒受径向拉应力,Al基体受径向压应力,平均残余热应力为121 MPa,小于X射线法测的平均残余应力131.7 MPa。Al-27%Si合金屈服强度与残余热应力、Si相形貌和大小有关。循环热处理后,当Si相形貌和尺寸相当时,材料的屈服强度随残余热应力的降低而升高;当Si相尺寸随热循环增大时,在残余应力相当的情况下材料的屈服强度降低。     

喷射沉积Al-17Si-5Fe-2Mn-2Ni-3.5Cu-1Mg-1V合金的组织及性能

采用喷射沉积快速凝固技术制备了Al-17Si-5Fe-2Mn-2Ni-3.5Cu-1Mg-1V合金,利用金相、X射线衍射和SEM等测试方法分析了合金的组织特征、热稳定性及力学性能。结果表明：喷射沉积合金的组织由大量弥散分布的粒状相、少量块状相和共晶基体组成。挤压态合金经300℃不同时间加热后,初晶Si相没有明显的粗化,热稳定性良好;合金经热挤压后,室温极限拉强度达232.2 MPa,经T6热处理后极限抗拉强度提高了17%,达271.3 MPa。     

喷射沉积耐热Al-15Si-5Fe-2Ni-3.5Cu-Mg-1.5Mn-V合金的组织与性能

采用喷射沉积快速凝固技术制备了Al-15Si-5Fe-2Ni-3.5Cu-Mg-1.5Mn-V合金,在480℃下进行热挤压,挤压比为8:1.采用光学显微镜以及扫描电镜对其微观组织进行观察,用X射线对其进行化学成分分析,并对喷射沉积挤压态合金的热稳定性、硬度进行测试.结果显示,喷射沉积工艺制备的Al-Si系合金组织均匀细小,初晶Si相的形状基本是颗粒状或块状.热挤压后合金组织致密,初晶Si相弥散分布在基体上.挤压态合金在300℃下初晶Si相没有明显长大,热稳定性良好.该合金在300℃下仍具有相当高的强度.     

显微组织对Al12Zn2.4Mg1.1Cu合金沉积态、挤压态力学性能的影响

利用喷射成形技术制备了Al12Zn2.4Mg1.1Cu高强铝合金,采用扫描电镜分析测试手段,对沉积态、挤压态合金进行了微观组织和拉伸断口分析.结果表明:实验合金沉积坯件组织由均匀细小的等轴晶组织组成,晶粒尺寸为10～20 μm;经热挤压后,其组织变得更加致密,晶粒更加细小,尺寸为2～3 μm.沉积态合金抗拉强度为358～361 MPa,屈服强度为332～336MPa,伸长率为6.9％～7.2％;经过挤压后抗拉强度为434～438MPa,屈服强度为394～397MPa,伸长率为8.1％～8.7％.沉积态和挤压态合金的断口断裂方式主要为韧性断裂.     

制备工艺对高硅铝合金的组织及性能的影响

采用熔炼铸造、真空包套热挤压、喷射沉积三种方法制备了Al-40％Si高硅铝合金锭坯，并通过光镜及扫描电镜对其组织进行分析。结果表明：真空包套热挤压工艺制备的样品其硅相细小。在挤压温度为490℃时。其Si相大小为2～10μm，且分布均匀弥散，初生硅相均匀分布在α基体相中。断口分析显示，真空包套热挤压高硅铝合金的断裂方式属晶内韧性断裂与沿晶断裂的混合型断裂。其力学性能也是这三种制备工艺中最优的，其抗拉强度高于170MPa，伸长率大于8％。     

喷射沉积Al-27%Si合金的半固态挤压成形

研究喷射沉积Al-27%Si合金的半固态挤压成形工艺及其对合金组织与性能的影响。结果表明:喷射沉积Al-27%Si合金在600℃下二次加热10~12 min后,合金液相体积分数适中,Si相尺寸相对细小,形貌为近球形,适合于半固态成形。经600℃二次加热10~12 min后,进行半固态挤压能消除喷射沉积合金中的孔隙,Si相比挤压前更加均匀细小,挤压棒材具有良好的表面质量和均匀的微观组织。经600℃二次加热12 min后,半固态挤压的合金可达到最高的相对密度(99.5%)、抗拉强度(195 MPa)和伸长率(6.7%)。     

制备工艺对高硅铝合金的组织及性能的影响

采用熔炼铸造、真空包套热挤压、喷射沉积三种方法制备了Al-40%Si高硅铝合金锭坯,并通过光镜及扫描电镜对其组织进行分析。结果表明:真空包套热挤压工艺制备的样品其硅相细小,在挤压温度为490℃时,其Si相大小为2～10μm,且分布均匀弥散,初生硅相均匀分布在α基体相中。断口分析显示,真空包套热挤压高硅铝合金的断裂方式属晶内韧性断裂与沿晶断裂的混合型断裂。其力学性能也是这三种制备工艺中最优的,其抗拉强度高于170MPa,伸长率大于8%。     

添加Mn和Mg对喷射沉积Al-12Si合金微观组织与性能的影响

针对微波组件用Al-12Si合金盖板材料中存在粗大针状Si相导致强度不足的问题,采用喷射沉积?热压制备Al-12Si和Al-12Si-1Mn-0.6Mg合金,对比分析添加1％Mn和0.6％Mg对合金微观组织、力学和热物理性能的影响.结果表明:热处理后,Al-12Si-1Mn-0.6Mg合金组织中Si相呈近球形颗粒均匀分...     

喷射沉积Mg-12.55Al-3.33Zn-0.58Ca-1.0Nd合金组织与力学性能研究

利用XRD、OM、SEM、TEM研究了喷射沉积Mg-12.55Al-3.33Zn-0.58Ca-1.0Nd合金挤压态的显微组织和合金的力学性能。结果表明:喷射沉积挤压态镁合金主要包含基体α-Mg和Al2Ca相,基体组织为等轴晶,平均晶粒尺寸为3μm;Al2Ca颗粒主要沿镁基体晶界分布,颗粒尺寸在1.0μm左右,并在Al2Ca相中存在孪晶结构;合金的σb、σ0.2、δ分别为450、325MPa,5%。在拉伸断口上存在大量石块状的Al2Ca相,表明合金的断裂方式为沿晶断裂;与经热挤压的铸造AZ91镁合金对比,该合金强度明显提高,但合金塑性降低;合金强度的提高主要来源于合金的细晶强化和Al、Zn对合金的固溶强化,而伸长率降低是由于合金中存在的大量Al2Ca颗粒是沿镁基体晶界分布,导致合金的塑性降低。     

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。