超声辅助TIG堆焊焊缝微观组织及力学性能研究

采用超声辅助钨极氩弧焊(U-TIG)和ER5356焊丝在5083铝合金板上进行堆焊试验,通过对比有无超声作用时的焊接热循环曲线分析了晶粒细化机理;并结合ANSYS软件分析了5083铝合金板表面的振动场分布,研究了距离超声源不同位置焊缝的微观组织及力学性能变化规律。结果表明:超声场的引入增大了冷却速度和熔池液态金属的过冷度,进而增大形核率,细化了晶粒,并抑制了热裂纹的产生。施加超声后试板不同区域的振幅不同,振幅大的区域的晶粒细化效果更加明显,焊缝的拉伸性能更优。     

超声振动对6061铝合金焊接热裂纹影响

为解决硬铝合金焊接接头软化严重的问题,选用7075铝合金作为填充材料对6061铝合金进行高组配焊接.焊接接头硬度确有提升,但在焊接过程中产生了热裂纹.文中设计了一个超声辅助平台将超声振动引入到传统的钨极氩弧焊中,在确保焊接接头硬度的条件下解决焊接热裂纹的问题.结果表明,超声功率较低时热裂纹消失,但超声功率达到480 W时,热裂纹再次产生.随着超声功率的增加,焊接接头的晶粒尺寸和形状发生了变化,熔合区的柱状晶被打碎,转变为较为细小的等轴晶,焊缝中心的等轴晶也发生了细化,在功率640 W时焊缝中心的平均晶粒尺寸最小.焊接接头中的析出相数量也随着超声功率的增大逐渐增多,分布逐渐均匀,对焊接热裂纹造成影响,因此存在一个超声功率的范围,能够同时解决焊接接头软化和焊接热裂纹的问题.     

UNS S31803双相不锈钢的焊接工艺

采用气体保护钨极氩弧焊(GTAW)对UNS S31803双相不锈钢焊接,研究其焊接工艺下焊接接头的相比例、焊缝和热影响区(HAZ)的力学性能,为我国00Cr22Ni5Mo3N双相不镑钢的现场焊接提供指导.     

紫铜厚大结构件钨极氩弧焊热裂纹形成机理

对紫铜厚大结构件钨极氩弧焊(GTAW)热裂纹形成机理进行了研究.对热裂纹的动态形成过程进行观察和分析,在普罗霍罗夫理论基础上优化了热裂纹形成判据,并建立了基于刚性拘束热裂纹试验的紫铜厚板GTAW有限元模型.结果表明,内部变形率Δε是促使开裂的内因,得到HS201焊缝金属在脆性温度区间内(BTR)的横向拉伸应力及Δε的变化规律,并与其高温延性进行对比,得到不预热工艺下热裂纹产生的原因.为了防止热裂纹的出现,模拟并分析了不同预热温度下HS201焊缝金属的Δε的变化规律,预热温度由500℃降为420℃即可避免热裂纹出现.     

CPR1000反应堆压力容器径向支撑块焊接质量的控制

通过金相显微镜、扫描显微镜和电子背散射衍射方法对一种大厚度NiCrFe-7熔化焊焊缝中的微裂纹进行了表征和机制分析,焊接方法分别为焊条电弧焊(SMAW)和钨极氩弧焊(GTAW). 结果表明,该种热裂纹为沿晶的再热裂纹,其形成是由于焊接热影响区在高温下发生应力松弛现象,导致晶界大尺寸MC型碳化物和氧化物处出现应力集中,造成裂纹沿这些颗粒内部或界面开裂. 相比于GTAW工艺,SMAW工艺的焊缝中存在大量氧化物,造成SMAW焊缝再热裂纹倾向高于GTAW焊缝,进而导致前者焊缝弯曲性能不符合国家标准要求. 通过此研究,建议采用保护气效果更佳的GTAW工艺.     

大厚度NiCrFe-7熔化焊焊缝微裂纹

通过金相显微镜、扫描显微镜和电子背散射衍射方法对一种大厚度NiCrFe-7熔化焊焊缝中的微裂纹进行了表征和机制分析,焊接方法分别为焊条电弧焊(SMAW)和钨极氩弧焊(GTAW).结果表明,该种热裂纹为沿晶的再热裂纹,其形成是由于焊接热影响区在高温下发生应力松弛现象,导致晶界大尺寸MC型碳化物和氧化物处出现应力集中,造成裂纹沿这些颗粒内部或界面开裂.相比于GTAW工艺,SMAW工艺的焊缝中存在大量氧化物,造成SMAW焊缝再热裂纹倾向高于GTAW焊缝,进而导致前者焊缝弯曲性能不符合国家标准要求.通过此研究,建议采用保护气效果更佳的GTAW工艺.     

钛合金超音频直流脉冲GTAW焊缝组织性能

基于1.5 mm厚Ti-6Al-4V(TC4)钛合金平板对接试验,研究分析了超音频直流脉冲氩弧焊焊缝金相组织及焊接接头力学性能.结果表明,与常规直流钨极氩弧焊(gas tungsten arc welding,GTAW)相比,由于超音频直流脉冲方波电流的作用,气泡逸出速度增大,Ti-6Al-4V钛合金焊缝的气孔敏感性降低,熔池高温液态金属流动性增强,电弧能量集中,焊缝晶粒细化明显,其亚晶组织以短棒状a’马氏体组成的网篮状组织或a’片状组织与短棒状a’相交织的状态为主,焊接接头断后伸长率和断面收缩率显著提高.     

紫铜衬垫在薄壁筒体焊接中的使用

脉冲钨极自动氩弧焊焊接薄壁圆筒形压力容器时,虽然由于线能量(热输入)容易控制,用悬空的单面焊双面成形工艺比连续电流钨极氩弧焊容易得到Ⅰ级焊缝。但是当工件的椭圆度较大时,焊接规范很难掌握,背面焊漏高度不易控制,尤其在背面焊漏高度要求较严时很难达到设计要求。为了保证焊缝质量,采用紫铜衬垫是一种较好的方法,而紫铜衬垫的尺寸规格对产品的质量则非常重要。我们的产品是一个1.5mm厚的薄壁     

塑性变形对BT20钛合金焊缝组织和力学性能的影响

分析塑性变形对BT20钛合金焊缝组织和力学性能的影响。试验采用钨极氩弧焊对接焊形式对BT20钛合金施焊;焊接接头的塑性变形试验在油压机上进行,变形过程中采用了双保温措施。结果表明：钨极氩弧焊是一种适合BT20钛合金的焊接方法,在其它焊接参数一致的情况下,电流越小,焊接质量越好;塑性变形加退火可显著改善BT20钛合金焊缝的材料组织、细化晶粒,提高焊缝金属材料的力学性能。     

不同焊接工艺下304不锈钢焊接接头组织及力学性能的研究

分别采用手工电弧焊(SMAW)和钨极氩弧焊(GTAW)对304不锈钢进行焊接,采用光学显微镜、显微硬度计、万能试验机对焊接接头的组织及力学性能进行了观察分析及测试。结果表明:两种焊接工艺焊接接头的组织均为奥氏体,SMAW焊缝区为粗大树枝晶,而GTAW的焊缝区为细小的树枝晶,焊缝与母材熔合良好;GTAW接头的显微硬度均高于SMAW,接头从焊缝区到热影响区到母材硬度均呈先上升后下降的趋势,SMAW和GTAW焊缝区的硬度分别为175 HV和205 HV;SMAW和GTAW接头的抗拉强度分别为623.6 MPa和690.7 MPa,断裂位置均为母材,弯曲试验合格,接头塑性良好;GTAW接头组织和性能优于SMAW。     

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。