常压/真空环境激光焊接焊缝成形特性及残余应力与变形对比

在高功率激光焊接中,采用增大激光功率的方法以获得更大熔深时,面临焊接过程稳定性差、焊接缺陷频发等问题,目前国内外普遍认为真空激光焊接是解决以上问题的有效手段. 文中采用工艺试验和数值模拟的方法,研究了常压和真空环境下中厚度全熔透激光焊接在焊缝成形及残余应力与变形分布的差异. 结果表明,降低环境压力可显著增加激光焊接熔透深度,真空环境可以将常压环境10 mm全熔透激光焊接所需激光功率从10 kW降低到6 kW,并获得更好的焊接质量. 常压环境和真空环境下,全熔透激光焊接工件展现出类似的横向残余应力、纵向残余应力和变形分布规律,但由于真空环境下热输入较低,焊缝深宽比大,焊后残余应力的峰值和变形程度均显著小于常压环境.     

基于弧压反馈的薄板GTAW智能熔透控制

薄板GTAW的熔透控制是保障其焊接质量的关键,而焊接熔透的智能传感与识别是其中的核心难题. 传统的焊缝背面直接视觉传感可以有效提取熔透控制信息,但是往往因为可达性受限而不能使用. 因此,文中对基于GTAW弧压电信号的传感焊接熔透进行研究,基于弧压反馈提取焊接熔透信号,进而调节焊接电流波形保证焊缝均匀熔透而不发生烧穿. 试验采用4 mm厚热轧钢板、3 mm厚冷轧钢板进行表面堆焊. 结果表明,在不同电流形式下堆焊试验中验证了控制原理,反馈智能调节,变散热条件以及变间隙试验均可得到较美观的焊缝.     

P元素加入形式对铁基金刚石工具胎体组织性能的影响

以常用的CuP8,FeP24两种预合金粉作为研究对象,运用SEM,EDS,硬度和抗弯强度等研究分析手段,研究了以不同形式加入P元素对铁基金刚石工具胎体组织性能的影响. 结果表明,烧结后胎体组织由α-Fe、含铁固溶体(Cu)、Fe₃C化合物组成,加入FeP24的烧结胎体中还存在Fe₂P和FeP化合物. P元素加入形式对胎体性能影响显著,向胎体中加入CuP8,P元素几乎全部脱离CuP8进入铁基体,相比于加入FeP24的胎体,P元素分布更均匀,胎体硬度、抗弯强度等性能指标均有提高. FeP24在热压过程中会产生微裂纹,这些微裂纹可能成为基体的裂纹源而降低胎体的抗弯强度. 因此,选用CuP8预合金粉更有利于获得高性能铁基金刚石工具胎体.     

Modelling of electron energy absorption and backscattering during EBW

A three-dimensional heat flux model for deep-penetrating electron beam welding (EBW) is established to mathematically describe the physical heat generation process during interaction between electrons and the dynamic molten pool free surface. Monte Carlo method is used to determine the electron-target interaction, and random distribution of initial electrons, progressive trajectory tracing and electron backscattering models are used to describe the spatial distribution of electrons absorption. The model is verified in preset keyholes and applied in the simulation on electron beam welding process, and the calculated bead shape shows a good consistency with experimental results.     

Extrusion process and property of AZ31 magnesium alloy

The microstructure and mechanical properties of extruded AZ31 magnesium at different extrusion temperature were investigated.The results show that,at 380 ℃,when the extrusion ratio is 23,the AZ31 magnesium alloy has a dense recrystallized microstructure and good mechanical properties.On one hand,if the extrusion ratio is too small,grain crushing effect is not obvious,and part of the grain is not dynamic recrystallization.On the other hand,larger extrusion ratio can lead to grain growth and banded structure.Tensile fracture characteristics of extruded AZ31 magnesium alloy is quasi-cleavage.     

304H焊接接头蠕变疲劳寿命预测

文中进行了温度680 ℃，具有保持时间的304H对接焊试样在超声波消应力、焊态固溶处理状态下的蠕变疲劳试验. 结果表明，超声波消应力处理不能改善失效寿命，固溶处理可以显著提高失效寿命，固溶处理失效寿命约为焊态的1.6倍，同时根据四种蠕变疲劳寿命预估模型建立了680 ℃304H不锈钢焊态蠕变疲劳寿命预估式，并对四种寿命模型寿命预测效果进行了比较，其精度由高到低依次是延性耗竭法、平均应变速率法、应变能频率分离法、延性耗竭与损伤力学法.     

Numerical analysis of influence of expansion joints on welding residual stress of an EGR cooler

The influence of expansion joints on the welding residual stress at the tube-plate junction of an exhaust gas recirculation (EGR) cooler was studied by numerical simulation method. The simulation results show that the expansion joints set on the housing of the EGR cooler mainly for the sake of protecting the tube-plate joints from bearing additional heating stress can also reduce the welding residual tensile stress. The expansion joints set on the EGR cooler can mitigate the tensile force acting on the edges of the main plates through its elastic extension, and thus reduce the magnitude of welding residual tensile stress at the tube-plate junction.     

T2纯铜大载荷超低速搅拌摩擦焊接头强韧化机理

采用大载荷超低速搅拌摩擦焊工艺对2 mm厚的T2纯铜进行焊接,利用光学显微镜、扫描/透射电子显微镜、电子背散射衍射、硬度测试以及静拉伸试验对焊接接头的微观组织和力学性能进行研究. 结果表明,焊接热循环得到显著改善,有效抑制了由焊后余热带来的退火软化作用,彻底消除热影响区. 搅拌区由含有大量孪晶组织的超细晶构成,搅拌区抗拉强度和断后伸长率分别较母材提高了94%和69%. 文中提供了一种简单有效的方法,可同时提高纯铜搅拌摩擦焊搅拌区的强度和韧性.     

多孔化高熵合金改善Al-Si合金/钢体系润湿铺展性能机理

借助电极感应熔化气雾化法,制备了 FeCoNiCrMn高熵合金粉末;通过真空烧结技术,在钢表面制备了具有不同孔隙率和孔径的多孔高熵合金涂层. 研究了不同烧结工艺对多孔涂层孔隙率、孔径以及过渡层厚度的影响. 开展了Al-12Si合金在多孔高熵涂层钢表面的原位润湿铺展试验,探讨了多孔高熵合金涂层对表观接触角和铺展行为的影响规律,深入分析了多孔高熵结构内反应产物的显微组织和相组成. 结果表明,随着烧结温度的升高和保温时间的延长,多孔高熵合金涂层的过渡层厚度逐渐升高,孔隙率及平均孔径逐渐减少. 液态Al-12Si合金液滴在多孔涂层中微通道增强的毛细力作用下,迅速浸润到多孔结构中,并实现了材料表面的完全润湿. 在高熵合金的迟滞扩散效应与高熵效应共同作用下, 界面反应层中金属间化合物的形成受到显著阻碍,界面相结构由富Cr的FCC、富AlFe的BCC以及富AlNi的B2 + 富Al的BCC共晶状结构组成.     

石墨烯纳米片对AgCuTi钎料熔点与润湿性的影响

采用球磨法在AgCuTi钎料中添加不同质量分数的石墨烯纳米片(GNSs)制备出复合钎料,利用差示扫描量热仪(DSC),SEM以及XRD等方法研究了微量的石墨烯纳米片对AgCuTi钎料微观形貌、熔点以及在蓝宝石表面润湿性的影响. 结果表明,球磨法对GNSs-AgCuTi复合钎料的物相没有影响,石墨烯均匀地分散在AgCuTi颗粒周围;复合钎料熔点随着石墨烯含量的增加而降低,当石墨烯含量为0.5%,熔点降低了3.2 ℃;微量的石墨烯,改善钎料在蓝宝石表面的润湿性,0.3%GNSs-AgCuTi复合钎料的润湿角减小了4.4°,铺展面积增加了10 mm2,而过多的石墨烯也使得复合钎料的润湿性变差;石墨烯与元素Ti反应生成TiC,复合钎料与蓝宝石界面反应产物为Ti₃Cu₃O相.     

C18000铜合金搅拌摩擦焊接头微观组织与性能

对3.5 mm厚的C18000铜合金板进行搅拌摩擦焊焊接试验. 在焊接速度120 mm/min,转速1 200 r/min工艺下获得无缺陷焊接接头. 在金相显微镜下对接头的宏观形貌、微观组织进行观察,用扫描电镜和透射电镜对母材和搅拌区组织进行观察分析. 结果表明,接头区大致分为母材区、热影响区、热力影响区和搅拌区,搅拌区晶粒细小均匀,热力影响区晶粒沿边界切线方向被拉长;搅拌区Cr₃Si相部分溶解,搅拌区组织中的Cr单质相和Ni₂Si相溶解导致接头硬度和抗拉强度下降. 搅拌区平均硬度为151.4 HV;接头抗拉强度为497 MPa,达到母材的72%;接头电导率下降为35%IACS.     

304LN不锈钢表面激光熔覆钴基合金组织和性能

为了提高304LN不锈钢的耐磨性,延长控制棒导向筒组件使用寿命,采用激光熔覆技术在304LN不锈钢表面制备了Stellite 6钴基熔覆层.利用光学显微镜(OM)、能谱仪(EDS)、显微硬度计、摩擦磨损试验机、腐蚀试验装置等多种试验测试设备,分析了熔覆层组织形貌、成分、显微硬度、摩擦磨损性能及腐蚀行为,确定了多道多层钴基熔覆层的工艺参数.结果表明,熔覆层与基体之间形成了冶金结合,显微组织主要由平面晶区、胞状和柱状晶区、树枝晶区和等轴晶区组成.熔覆层硬度为500 ~ 550 HV,摩擦磨损系数为0.30 ~ 0.35,熔覆层均匀腐蚀速率和缝隙腐蚀速率分别为0.153 和0.143 mg/(dm2·d). 激光熔覆钴基合金可以有效提高304LN不锈钢表面的硬度、耐磨性能和耐腐蚀性能.     

Characterizations of friction welding joint interface for AISI 316

Because of heat amount is different from peripheral to central of friction welding interface, which is leaded to vary the characterizations along that interface. Current study, respectively, focused on the effect of different friction pressure on micro-structural and mechanical properties of that friction welding joint interface. Presently, these friction pressures are 110, 130, 150 and 170 MPa while kept all other conditions constant. The effects of different friction pressure on welding interface characterization were investigated by EDX, SEM, tensile, compression, impact and hardness tests. The tensile tests carried out on the standardized test piece with diameter 6 mm and 8 mm, thus, compression tests were extracted from the positions of 0°, 45° 90° with test specimen of 4 mm diameter and 6.5 mm length at weld center. Whereas, the impact test pieces were picked up in two positions, the first one is symmetrical, which it obtained to the respect of the rotation axis and the interface, on the other hand, the second one is non-symmetrical with the axis of rotation and symmetrical to the interface, for making the notch head coincide with the center of the welded joint, The obtained results showed that with reducing of friction pressure will present lack of bonding increasing from peripheral toward the welding center, which will responsible on reducing of the mechanical properties such as tensile, compression and impact strength.     

45钢电子束扫描表面W合金化组织和硬度

电子束扫描表面合金化技术可以改善钢铁材料的组织及性能. 采用等离子热喷涂技术和电子束扫描技术对45钢表面进行熔覆合金化处理. 研究电子束扫描对强化层组织和硬度的影响,探讨了电子束功率、扫描速度对强化层组织和硬度的影响规律. 结果表明,45钢经表面合金化处理后,其表面可分为合金化区、热影响区和基体区. 合金化区的显微组织为针状马氏体和碳化钨颗粒,硬度为1 250 HV,是基体硬度的5倍. 热影响区的组织为针状马氏体和铁素体,硬度为860 HV,是基体的3倍. 基体区的组织为珠光体和铁素体. 电子束工艺参数对强化层组织和硬度有较大影响,强化层厚度随电子束功率的增加而增大,随着扫描速度的增加而减小.     

Cold cracking susceptibility of X100 pipeline steel

The y-groove Tekken test has been performed to evaluate the cold cracking susceptibility of X100 pipeline steel. The impact of preheating state on the microstructure, distribution of hardness, and the stress-strain state in the welded joint was analyzed. The results show that X100 pipeline steel reveals a low susceptibility to cold cracking with cracking ratios below 20%. It is found that elevated preheating temperature leads to longer cooling time in the welded specimen and ultimately results in a lower cold cracking susceptibility. Preheating temperatures of up to 100 ℃ are favorable in decreasing the cold cracking susceptibility due to a relative fine microstructure and low M-A constituent amount in coarse grained heat affected zone, a low hardenability, and low-level residual stress and strain. However, excessive preheating temperatures of 150 ℃ and 200 ℃ lead to grain coarsening, higher M-A constituent amount, higher residual stress level and increasing strain level in the Tekken specimens. Preheating temperature above 150 ℃ is not favorable for decreasing the cold cracking susceptibility of X100 steel.     

超低银SAC钎料焊点界面显微组织演化

研究了复合添加Ga/Nd元素的超低银Sn-0.3Ag-0.7Cu钎料在长期时效过程中的微焊点界面组织演化情况. 结果表明,复合添加适量Ga/Nd元素可以显著改善时效后微焊点界面组织,抑制微焊点界面附近大块状金属间化合物以及稀土相的生成. 经720 h时效后,即使在含有过量Nd元素的微焊点界面仍没有发现明显的Ag₃Sn相和稀土相,取而代之的是小块状的新相,结合EDS和XRD分析结果推测该相含有Ga₂Nd与Cu₆Sn₅. 经过长期时效处理后,微焊点抗剪力接近Sn-3.8Ag-0.7Cu焊点抗剪力的90%,具有较好的力学性能.     

送丝位置对铝/镀锌板CMT搭接接头组织与性能的影响

采用CMT搭接方法研究不同送丝位置对6082铝合金/镀锌板搭接接头质量的影响. 使用金相显微镜、扫描电镜(SEM)、能谱仪(EDS)分析焊接接头的形貌,微观组织及元素分布;通过拉伸试验检测接头的力学性能. 结果表明,1和2位置时,焊缝成形不饱满,锌层蒸发严重,界面处形成FeAl₂,FeAl及FeAl₃的金属间化合物,承载力达到6 kN;当3,4和5位置时送丝位置指向铝板,焊缝成形饱满,界面处形成Fe_6.6Al₃Zn_0.2和Fe₂Al₃Si_0.3,厚度约为2 μm,承载力达到7.5 kN,综上所述,CMT焊接铝合金/镀锌板时送丝位置应偏向铝板,可得到综合性能更好的焊接接头.     

胶层-镍箔辅助激光焊钢/镁接头组织与性能

采用钢板在上、镁板在下且添加胶层-镍箔辅助的激光焊接技术,对厚度1.4 mm的DP590双相钢和厚度1.5 mm的AZ31B镁合金进行焊接, 基于热力学计算选择添加箔片元素,分析接头焊缝形貌、显微组织与力学性能,并对接头熔池温度场和流场进行数值模拟. 结果表明,激光功率1 800 W,焊接速度30 mm/s,离焦量为 + 2 mm,流量为15 L/min的氩气保护的工艺条件下,添加镍箔实现了镁/钢冶金连接,同时添加胶层和镍箔,与单一添加镍箔相比,接头平均抗剪强度提高1.73倍;添加胶层,焊缝连续光滑, 镁侧熔池的熔化宽度增大,钢/镁横向结合面积增加,熔池温度梯度降低,熔池流动速度提高,促进了界面元素相互扩散和冶金反应,因此钢/镁接头性能得到大幅提升.     

滚动轧制对铝合金搅拌摩擦焊接头性能的影响

采用自制滚动轧制头对5 mm厚铝合金7050搅拌摩擦焊接头的上表面及背面进行滚动轧制,并与其焊接态的接头作对比,研究了滚动轧制对焊接接头性能的影响. 结果表明,滚动轧制后接头表面的粗糙度由最大9.58 μm降低到平均约0.85 μm. 表层发生了剧烈的塑性变形,晶粒明显细化形成约200 μm厚的细晶层,亚表层晶粒细化程度降低,在焊核区伴有剪切带产生. 接头表层硬度明显提高,其平均硬度高达HV210,相比轧制前硬度HV110提高了91%. 接头表层残余应力由原来的拉应力转变为压应力,最大残余压应力场深度约为200 μm. 疲劳源由表层移至亚表层,疲劳寿命显著提高.     

Effect of heat input and filler metals on weld strength of gas tungsten arc welding of AISI 316 weldments

The present work investigates the effect of filler metals and heat input on weld bead geometry and mechanical properties of alloy316 welded by using GTAW.ER309 L,ER316 L and ERNi Cr Mo-3 filler metals,are applied to study their effect on the weldment.Weld defects are examined using radiographic testing.The mechanical properties of welds are evaluated through uniaxial testing,hardness measuring,and bending test.The mechanical properties and cooling rate decrease with increasing heat input.Tensile strength,yield stress and percentage elongation of weldments using three fillers are determined.Best results are obtained using ERNi Cr Mo-3.Besides,weld nugget area,cooling time and solidification time increases with increasing heat input.Finally,applying bending test on weld samples,cracks,tearing and surface defects are not observed.