低频电磁场对半连续铸造Al-Mg-Si-Cu合金显微组织的影响

采用低频电磁场半连续铸造工艺制备Al-Mg-Si-Cu铝合金铸锭,研究了低频电磁场对Al-Mg-Si-Cu铝合金铸锭组织的影响。结果表明,施加低频电磁场可以细化Al-Mg-Si-Cu铝合金铸锭的晶粒组织,减轻晶内元素的偏析程度。与常规半连续铸造相比,施加频率为20 Hz、电流为120 A的交变电磁场后,铸锭中的等轴晶组织增多,枝晶状组织减少,晶粒尺寸变得更加细小,铸锭边部和中心平均晶粒尺寸由常规半连续铸造的170和259μm分别降至133和187μm,同时有利于提高溶质元素在晶内的分布,很大程度上减轻了溶质元素的偏析。此外,低频电磁场的电磁振荡使得液穴内部温度场和流动场更趋均匀,溶质元素分配系数增大,结晶区间变小,抑制了树枝晶的生长,促进了Al-Mg-Si-Cu合金半连续铸锭中非枝晶组织的形成和溶质元素的强制固溶,并且抑制了溶质元素的偏析。     

电磁振荡对铝合金半连铸坯微观组织及溶质元素晶内含量的影响

研究了电磁振荡作用下7075铝合金半连铸坯微观组织及溶质元素的晶内分布，对其细化、非枝晶组织形成及溶质元素晶内含量的影响机制进行了探讨。认为在电磁振荡作用下，熔体中结晶核心增加，游离晶粒的枝晶生长方式得到抑制是形成均匀细小的近球形和蔷薇形非枝晶组织的原因，并从电磁场改变7075铝合金凝固过程中的溶质分配系数、结晶间隔、液穴内部温度场、流动场以及微观组织形貌等方面出发，分析了电磁振荡对溶质元素晶内含量的影响。     

电磁振荡对半连铸7075Al合金的宏观偏析的抑制作用

研究了电磁振荡作用下半连铸7075Al合金铸锭微观组织及溶质元素在截面上的宏观分布规律,结果表明：在适当的电磁频率范围内（10-30Hz）,随着交变磁场感应线圈电流强度增加,铸坯中近球形组织增多,蔷薇型组织减少,晶粒整体尺寸变得更加细小和均匀,铸锭表面质量明显提高,宏观偏析现象在很大程度上得到了抑制和消除,从电磁振荡使得初凝壳高度降低、液穴深度变浅、温度场和浓度场趋于均匀、非枝晶化程度提高、溶质元素平衡分配系数增大,结晶区间变小等因素出发,首次尝试性对电磁振荡的宏观偏析抑制作用进行了解释和说明。     

电磁振荡频率对上引连铸Cu-15Ni-8Sn合金组织及逆偏析的影响

通过在上引连铸Cu-15Ni-8Sn(质量分数,%)合金过程中施加电磁振荡,研究了电磁振荡频率对合金凝固组织及逆偏析的影响。结果表明:当施加的电磁振荡频率为10或30Hz时,合金的宏观凝固组织发生了柱状晶到等轴晶的转变,微观凝固组织由树枝晶转变为蔷薇状组织;当电磁振荡频率从30 Hz增加到50 Hz时,宏观凝固组织又逐渐转变为柱状晶,微观凝固组织也随之转变为发达的树枝晶。电磁振荡频率为10和30 Hz时形成的等轴晶组织有利于改善合金中Sn元素的逆偏析。电磁振荡使合金熔体中产生往复强制对流,10或30 Hz频率的电磁振荡引起的宽幅往复流动使固液界面前沿温度场和溶质场均匀,有利于形成等轴晶,并促使枝晶折断,形成游离晶,消除定向枝晶通道,从而抑制了逆偏析。而在50或100 Hz频率下,电磁振荡频率过高形成了窄幅往复流动,不能有效折断枝晶、达到细化晶粒的目的,从而减弱了抑制逆偏析的作用。     

电磁场对2524铝合金扁铸锭微观组织和宏观偏析的影响

采用在常规结晶器上布置线圈而开发的低频电磁半连续铸造技术（LFEC）制备2524铝合金扁铸锭并系统研究其对微观组织和宏观偏析的影响。结果表明,采用低频电磁半连续铸造技术制备的扁铸锭具有更加细小、均匀的铸态组织,而且组织由枝晶和蔷薇型转变为等轴晶组织。低频电磁半连续铸造技术对铸锭宏观偏析具有重要的影响,施加磁场后铸锭中心部分的反偏析明显减弱了。同时,对这些作用的机理进行了探讨。     

超声半连铸下7050合金大扁锭的微观组织及宏观偏析行为

在500mm×1320mm的7050铝合金扁锭铸造中引入超声外场,研究常规铸造与超声铸造下的微观组织形貌、分布和宏观偏析特征。结果表明,超声外场可以有效减小晶粒的尺寸、抑制组织中粗枝晶的产生并促进铸锭内组织的均匀分布;同时,加入超声场后,溶质元素Zn、Mg、Cu沿长度方向和宽度方向对称轴的偏析指数分别由0.1013、0.1117、0.1260和0.1119、0.1113、0.1281减小到0.0835、0.0790、0.1027和0.0743、0.0725、0.0841,沿铸锭不同方向的宏观偏析均得到有效弱化。超声的空化和声流作用改变液穴中的温度场和流场,改善晶体的形成环境,促进溶质元素的均匀分布,从而细化组织、弱化宏观偏析。     

提高LF6合金均火温度对均火过程的影响

直接水冷半连续铸造生产的铸锭,由于不平衡冷却和温度过冷、浓度过冷,合金凝固结晶时必然发生溶质元素的再分配,在铸锭显微组织上存在枝晶偏析,在晶界和枝晶间界上存在不平衡共晶,难熔元素在晶内过饱和。这种组织状态不仅降低铸锭的加工工艺塑性,降低合金的耐电化学腐蚀性能,同时也影响加工材的组织和力学性能。为了克服以上弊病,通常将铸锭进行组织均匀化处理。     

超声作用下半连铸7050铝合金的偏析行为及形成机制

采用SPECTRO-MAXx立式直读光谱仪和Leica金相显微镜,研究超声功率对半连铸过程中7050铝合金微观组织及溶质Zn元素径向分布的作用规律。结果表明:在超声外场作用下铸锭组织明显细化,混晶减少,溶质Zn元素的径向逆偏析程度减弱,并随着超声功率的增加,晶粒细化程度及宏观偏析的弱化效果更好,溶质Zn元素的偏析比由未加超声时的1.190降低为240 W功率超声作用时的1.086;在超声外场调控下,铝合金熔体偏析弱化的主要原因是由于形核率增加,晶粒细化,两相区液固相相对运动速度减小;液穴变浅,由铸锭收缩导致的富集液相径向流动减弱,是径向偏析程度减弱的另一原因;在半连续铸造过程中,采用超声外场控制液相的流动是弱化铸锭径向宏观偏析的有效手段。     

电磁搅拌对Incoloy825合金凝固组织和偏析的影响

研究了电磁搅拌对Incoloy825高温合金凝固组织及凝固过程中溶质元素偏析的影响。结果表明,在合金凝固过程中,施加电磁搅拌能够有效细化晶粒组织,同时增加等轴晶比例。当电磁搅拌电流强度由150A增加到300A时,铸坯中晶粒尺寸由300μm减小至210μm,同时等轴晶含量由66.7%增至77.5%。未施加电磁搅拌的Incoloy825高温合金铸坯内部的宏观偏析和微观偏析均比较严重,通过施加电磁搅拌,引起熔体强制对流,使熔体内部传热和传质得到改善,同时增大了冷却速率使二次枝晶臂间距减小,并促进液穴内熔体成分的均匀化,大幅度降低了合金元素的偏析程度。     

电磁铸造Al合金过程中液穴及微观组织的研究

对CREM法半连铸7075铝合金过程中，熔体弯月面形状、微观组织结构、溶质元素分布随磁场强度及磁场频率的变化规律进行了试验研究。结果表明：随着磁场强度的增大及磁场频率的减小，初凝壳形成位置点降低，液穴深度变浅，溶质元素晶内含量显著增加，固溶程度和硬度得到提高，相应地，铸锭中近球形组织增加，蔷薇形组织减少，整体组织变得更加细小和均匀。     

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。