焊接工艺对5A66铝合金接头组织与性能的影响

分别采用钨极惰性气体保护焊(TIG焊)和冷金属过渡焊(CMT)焊接5A66铝合金。为研究焊接方法对接头的影响,使用光学显微镜、扫描电子显微镜、显微硬度测试仪和万能试验机对焊接接头进行了测试。试验结果表明,CMT接头强度达到母材的93%,高于TIG焊接头强度7%;CMT接头断裂在热影响区位置,TIG焊接头断裂在焊缝位置。另外,CMT热输入小,热影响区软化程度低,力学性能与母材相差不大。在试验条件下CMT焊工艺焊接接头的性能优于TIG焊接头。     

304不锈钢TIG焊与激光焊工艺对比研究

采用TIG焊与激光焊分别进行304不锈钢平板对接试验,通过万能试验机、显微硬度计、光学显微镜(OM)、扫描电镜(SEM)、X射线荧光衍射(XRD)等对比分析2种焊接工艺条件下焊接接头理化性能。结果表明:2种焊接工艺下304不锈钢焊接接头成形良好且无明显缺陷;激光焊焊缝面积、正反面熔宽更小; 2种焊接工艺的焊缝组织均为奥氏体和δ铁素体树枝晶组成,但激光焊树枝晶数量更多、尺寸更加细小;激光焊和TIG焊拉伸试样断裂位置均在焊缝区,但激光焊抗拉强度和伸长率更大,断口韧窝更细小均匀且更深,激光焊焊缝相较于TIG焊的塑韧性更好;激光焊接头的焊缝区显微硬度整体高于TIG焊接头焊缝区的显微硬度,由于晶界强化作用,2种焊接工艺的焊接接头显微硬度的最大值均出现在熔合区附近。     

焊接方法对C24S铝锂合金组织和性能的影响

对2 mm C24S铝锂合金薄板进行TIG焊和FSW焊接试验,焊后利用光学显微镜(OM)和扫描电镜(SEM)观察分析两种焊接方法所得接头的显微组织,并测试其室温拉伸性能和显微硬度。结果表明:TIG焊所得接头组织粗大,焊缝气孔缺陷严重,焊缝区强化相大量溶解,接头抗拉强度仅为母材的47.9%,焊缝显微硬度为92 HV,且拉伸接头塑性较差;FSW焊焊缝成形良好,接头组织细小,且焊缝强化相并未溶解,接头拉伸强度达到母材的82.6%,焊缝显微硬度高达115 HV,接头塑性良好。     

Al-Mg-Si 6082合金氩弧焊焊接接头的力学性能与微观组织

对3mm和10mm厚的Al-Mg-Si 6082合金分别进行了TIG焊和MIG焊,获得了成形良好、表面无裂纹、气孔和咬边等缺陷的焊接接头。研究了TIG焊和MIG焊时焊接接头不同区域的显微组织特征,通过拉伸和硬度试验,分析了焊接接头的力学性能,并研究了TIG焊和MIG焊时焊接接头拉伸断口的微观形貌。结果表明,焊缝中心为细小的等轴晶,靠近熔合线的焊缝区为柱状晶,而热影响区出现了无沉淀析出带,且晶粒出现了不同程度地长大;MIG焊焊接接头的抗拉强度和伸长率均高于TIG焊;焊接接头的硬度沿焊缝中心呈对称分布,焊缝区的硬度几乎与母材相当。     

2A12铝合金TIG焊接头组织性能分析

采用普通交流TIG焊和随TIG焊旋转挤压两种方法对2A12铝合金薄板进行焊接,分别对焊接熔合区、热影响区和焊缝区的显微组织进行晶相分析.结果表明,与普通交流TIG焊相比,随TIG焊旋转挤压法对变形和气孔的控制效果较好,得到的焊缝组织品粒细小而均匀,有效降低了残余应力,提高了焊接接头的力学性能.对焊接接头进行拉伸试验,拉伸试样断裂的位置均为焊缝区,焊缝在冷却过程中由于偏析而生成的低熔点共晶θ相和S相使得力学性能下降,且随焊旋转挤压法焊接接头的抗拉强度和屈服强度约为普通交流TIG焊接头的1.2倍.     

焊接工艺对2024铝合金接头组织与性能的影响

研究了分别采用熔化极氩弧焊(MIG)和钨极氩孤焊(TIG)进行2024铝合金焊接的工艺,并对在两种工艺条件下获得的接头的力学性能和微观组织结构进行测试分析.试验结果表明,MIG焊接头的抗拉强度达到母材抗拉强度的60%以上,而TIG焊接头的抗扭强度只达到母材抗拉强度的50%,这是由于MIG焊接头焊缝组织要比TIG焊接头焊缝组织细小,晶界处共晶相数量明显减少,晶内析出了很多细小的共晶相,有利于提高接头强度;且MIG焊的热输入比TIG焊的热输入小,MIG接头软化程度也比TIG焊要小.因此在试验条件下,MIG焊工艺获得接头的性能要优于TIG焊接头.     

LF6铝合金A-TIG焊与TIG焊接头对比研究

采用A-TIG焊和TIG焊两种不同的焊接方法对LF6铝合金进行对接焊。A-TIG焊采用小电流,TIG焊采用大电流,通过金相分析、拉伸断口扫描、EDS分析以及电子探针元素分析等一系列手段分析焊接接头在显微组织和力学性能以及元素分布上的差异。试验结果表明:A-TIG焊焊缝处组织与TIG焊相比更为粗大,且焊缝处的硬度也相对更高。A-TIG焊焊接接头的拉伸性能整体高于TIG焊。分别分析A-TIG焊及TIG焊的热影响区和焊缝区的元素,结果表明这两种焊接方法对热影响区及焊缝区域元素的影响几乎没有差别。     

Inconel 600热电偶套管焊接的组织和性能研究

采用等离子和TIG分别对Inconel 600热电偶套筒进行焊接,研究不同焊接方法对Inconel 600显微组织及其性能的影响。母材为全奥氏体组织,主要由γ、γ′(Ni_3Al)以及Cr_(23)C_6碳化物组成,夹杂着些许氧化物颗粒。结果表明,等离子接头中析出的碳化物Cr_(23)C_6多于TIG焊接头,热影响区碳化物Cr_(23)C_6含量减少。焊缝显微硬度均低于母材,但等离子接头的焊缝显微硬度略大于TIG焊焊缝。     

9Ni钢焊接接头裂纹尖端张开位移试验研究

通过CTOD试验测试了液化天然气(LNG)储罐用9Ni钢埋弧焊(SAW焊)和TIP-TIG焊(简称TT焊)焊接接头的断裂韧性,分析了接头组织对断裂性能的影响。结果表明：SAW焊和TT焊接头CTOD值均能够满足相关工程标准要求,焊接接头达到失稳破坏时,TT焊接头需要更大的力,接头强度更高;SAW焊焊缝金属以长条状的胞状树枝晶为主,其间胞状晶,TT焊焊缝金属为细小均匀分布的胞状晶构成,细小均匀分布的胞状晶能够增加裂纹扩展抗力,利于提高焊缝金属韧性;TT焊应用于LNG储罐立焊缝,不仅可以去除打磨清根环节,还具有与SAW焊相当的焊接效率和焊接质量,自动化程度高,因此,具有很高的发展潜力。     

焊接方法对2219板材组织和力学性能的影响

分别采用搅拌摩擦焊(FSW)和钨极氩弧焊(TIG)对2219铝合金大型锻环上切取的板材进行焊接,通过维氏硬度和拉伸试验对焊接接头的室温力学性能进行了测试,并采用金相显微镜和扫描电镜等手段对接头的显微组织进行了观察。结果表明,两种焊接方法都使2219铝合金的硬度、强度和塑性下降,FSW焊接接头的硬度、强度明显高于TIG焊接接头,但是塑性相当。这是由于FSW焊缝处的组织相对于TIG焊更加细小,而且分布有一定数量的析出相。FSW和TIG焊接接头的断裂模式为韧性和脆性混合断裂。FSW和TIG焊接接头断裂位置分别为热机影响区和熔合区。     

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。