Effect of Friction Stir Processing on Microstructure and Mechanical Properties of Cast AZ31 Magnesium Alloy

对铸态AZ31镁合金进行单道次和双道次搅拌摩擦加工,对其微观组织和力学性能进行研究.结果表明:铸态AZ31镁合金搅拌摩擦加工后,共晶网状β-Mg17Al12相破碎并发生固溶,微观组织显著细化和均匀化.AZ31镁合金母材和单道次搅拌摩擦加工后的试样没有择优取向,而双道次搅拌摩擦加工后的试样存在择优取向,其(0002)基平面与试样表面平行.单道次和双道次搅拌摩擦加工后试样的抗拉强度分别提高了43和82MPa,延伸率提高了4.3％和11.9％.搅拌摩擦加工后试样的拉伸断口表现为韧性断裂特征.     

热处理对搅拌摩擦加工AZ91镁合金显微组织和力学性能的影响

对AZ91镁合金铸板进行搅拌摩擦加工,研究热处理对被加工材料组织和力学性能的影响。结果表明,经413℃保温16h固溶处理后,铸态合金晶界处粗大的网状β-Mg17Al12相基本溶入α-Mg基体中。在搅拌摩擦加工过程中,组织发生明显细化,产生细小的等轴状再结晶晶粒。预先固溶处理可使摩擦加工合金晶界处少量未溶β-Mg17Al12相全部溶入基体。随后时效处理导致β-Mg17Al12相以两种方式析出,时效初期以晶界处非连续析出为主,然后再发生晶粒内部的连续析出。时效处理可较大程度地提高合金的硬度,以16h最为显著,搅拌区平均显微硬度的最大值为118.4HV。预先固溶处理可以提高搅拌摩擦加工合金的塑性,伸长率为31.5%;随后时效处理(16h)则可以大幅度提高合金的抗拉强度,由搅拌摩擦加工板的265 MPa增至340 MPa。     

非平衡凝固AZ91+0.75%Er镁合金及其热处理

采用铜模喷铸技术制备出AZ91+0.75%Er(质量分数)稀土镁合金非平衡凝固试棒,研究了低温时效及高温固溶对合金组织和显微硬度的影响规律。结果表明,稀土元素的添加及冷却速率的提高均有利于细化AZ91镁合金组织,其中后者影响效果更加明显。急冷条件下的溶质截留效应还可以消除铸态稀土镁合金中的Al-Er针状化合物相。非平衡凝固合金经200℃时效处理后,β相从过饱和固溶体中析出。时效16 h后,Mg-Er稀土化合物相以颗粒团聚状从基体中形成。420℃固溶处理时,非平衡凝固合金中β相发生溶解,晶粒形貌转变为多边形等轴晶组织,平均晶粒尺寸随固溶时间的延长而不断增加。非平衡凝固及后续时效处理可有效提高稀土镁合金的显微硬度,而固溶条件下合金硬度值有所降低。     

热处理对挤压变形AZ61M镁合金的组织与力学性能影响

为研究热处理和热成形工艺对铸态镁合金的力学性能影响,采用不同保温时间对铸态镁合金AZ61M进行固溶处理,利用金相显微镜和显微硬度计研究不同固溶时间对镁合金组织和力学性能的影响,利用万能试验机对固溶后镁合金进行3道次多向挤压。结果表明:经过6 h固溶处理后,铸态镁合金AZ61M中的第二相β充分溶入基体,抗拉强度从64提高到244 MPa,硬度略有下降。固溶时间从6 h延长到10 h对提高力学性能作用不大,且延长保温时间使晶粒有长大粗化倾向。将固溶10 h的镁合金进行3道次多向挤压后,晶粒尺寸从200减小至100μm以下,抗拉强度和抗压强度相比未挤压前分别提高19%和44%。在单向拉伸/压缩过程中,裂纹扩展途径显示为穿晶断裂,且压断断口比拉断断口平滑。     

焊前固溶处理对铸态AZ91镁合金搅拌摩擦焊接接头组织和性能的影响

对AZ91镁合金进行了直接搅拌摩擦焊接及焊前预固溶搅拌摩擦焊接实验。采用扫描电镜(SEM)、透射电镜(TEM)、电子探针(EPMA)和拉伸实验等分析了焊接接头的微观结构和力学性能。结果表明：直接搅拌摩擦焊接后接头搅拌区的微观结构由于晶粒细化和粗大第二相的破碎、溶解及再析出而得到改善，然而大量粗大的β相在焊缝后退侧过渡区连续性聚集，使得该β相与基体之间的界面成为裂纹萌生源。直接搅拌摩擦焊接头的拉伸强度及断后伸长率分为136.68 MPa和2.34%,对铸态AZ91镁合金在400℃固溶12 h后，其焊接接头的拉伸强度及断后伸长率分别为184.81 MPa和6.79%。尽管焊前预固溶搅拌摩擦焊接接头的搅拌区平均晶粒尺寸较直接焊接接头的稍大，但是微观结构较直接焊接更加均匀。说明预固溶处理能够显著改善焊缝区域第二相的分布，使镁合金变形协调性增加，显著提高了焊件的强度和塑性。     

混合稀土对AZ91镁合金组织和性能的影响

在ZA91镁合金基础上添加不同含量的混合稀土（MM），对其铸态和固溶时效的组织及性能进行了研究。结果表明，MM显著改变AZ91合金的铸态组织，使Mg17Al12相细化，并出现针状相，从而使硬度，强度提高，但冲击韧度值及伸长率下降，进一步的固溶时效证明该针状相并不固溶于基体中，MM的加入，推迟了AZ91的时效硬化过程。     

Cd、Sb、RE对AZ31镁合金铸态组织及力学性能的影响

通过正交试验设计,研究了Cd、Sb、RE复合加入对AZ31镁合金铸态组织和力学性能的影响.Cd、Sb、RE复合加入后,AZ31镁合金铸态组织由富Al的α-Mg基体和均匀、弥散分布的析出相β-Mg17Al12、CeSb及Al11Ce3组成,Cd固溶干基体不形成新相.通过分析,得出对综合力学性能影响最优的试验方案是:Cd含量0.7%,Sb含量0.3%,RE含量0.3%;与AZ31相比,抗拉强度、伸长率、布氏硬度分别提高了22.9%、17.6%、5.9%.     

Mg-Al-Zn-Sm耐热镁合金的组织与力学性能

利用光学显微镜、扫描电镜和X射线衍射仪分析了铸态和固溶态AZ61和AZ61-2Sm合金组织形貌和相组成,测试了其硬度和拉伸力学性能。结果表明,向AZ61合金中添加2%Sm后,铸态组织有所细化,β-Mg17Al12相数量减少和尺寸变小,同时生成小块状的高热稳定性相Al2Sm。经固溶处理后,β-Mg17Al12相完全固溶于α-Mg基体中,只存在Al2Sm相。铸态和固溶态室温拉伸力学性能与AZ61合金相当,而铸态高温拉伸力学性能却显著提高,经固溶后得到进一步提高,与铸态室温相当。     

热处理对细晶AZ91D镁合金组织和性能的影响

采用MEF-3金相显微镜、JSM-6700F扫描电镜、EMPA-1600电子探针以及WDW-100D型电子万能实验机等,对经Al-Ti-B细化处理的AZ91D镁合金铸态组织及固溶-时效态的显微组织和力学性能进行了观察和分析。结果表明：分布在铸态AZ91D镁合金晶界的网状β-Mg17Al12相在T4热处理过程中逐渐溶解,使得合金的硬度下降,而抗拉强度升高;T6热处理后,合金组织中出现不连续析出与连续析出的β-Mg17Al12相,使得抗拉强度和硬度明显提高;不同的热处理使合金的断口发生明显变化。     

均匀化退火对AZ91D镁合金组织与性能的影响

为改善铸态AZ91D镁合金的不均匀组织,对铸态试样进行了均匀化退火处理.结果表明,经380-420℃, 8～40h的均匀化处理后,枝晶偏析大部分消除;再经缓慢冷却,β相以细小的针状或层片状脱溶析出.经布氏硬度测试,退火析出后合金硬度由铸态的67.5HB提高到80HB;力学性能测试结果表明,经均匀化退火处理后合金的屈服强度变化不大,抗拉强度由铸态的173MPa增加到259MPa,伸长率则由2%增加到8%.p相形态及分布的改变是AZ91D镁合金力学性能增强的主要原因.     

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。