航空发动机转子组件电子束焊变形预测

航空商用发动机组件尺寸精度要求较高,且组件焊接后盘心位置不能进行机械加工,因此采用数值模拟的方法对转子组件进行焊接变形预测. 试验将基于热弹塑性理论计算提取固有应变数值;通过理论计算得到GH4169合金电子束焊缝的固有应变值,分析焊接工艺参数对焊缝固有应变的影响规律;建立结构件模型,分析焊接工艺、焊接顺序及工装条件下组件焊接变形. 结果表明,相比于第一,第二和第三级盘,第四级盘心轴向变形最大,且通过增大扫描速度和改变约束方式的方法可以有效减小焊接变形,从而完成对转子组件焊接变形进行预测和控制.     

搅拌摩擦焊三维粘塑性热力耦合有限元数值模拟

针对搅拌摩擦焊(friction stir welding,FSW)的特点,建立了基于固体力学的刚粘塑性热力耦合有限元方程,并采用网格局部加密自适应跟随技术对FSW过程进行数值模拟,获得了焊接过程的温度、应力、应变分布特征及金属流动规律,预测焊接过程中所产生的缺陷.结果表明,FSW过程中试件的温度分布不对称,应变沿板厚的方向分布不一致,焊缝区产生了剧烈的塑性变形,因此FSW是一个典型的三维剧烈的塑性变形过程,热塑性变形机制是焊接接头形成的主要机制.     

薄不锈钢板激光焊接变形分析及控制

为了预测薄不锈钢板激光焊接变形量,并根据预测值采取措施来减小焊接变形,先要分析焊接过程中刚性约束作用、刚性约束和反变形同时作用两种条件下的残余塑性应变,用残余塑变理论计算焊接变形,再把计算值作为预变形量来设计专用夹具。在焊接前对工件施加对应量的反变形,进行激光焊接实验,再用三坐标测量仪测量焊接件。实验结果表明:通过使用夹具对整个工件进行刚性约束和反变形约束,变形量明显减小,跟用残余塑变理论计算出的值基本吻合,工件满足焊接要求。通过对实例的分析,表明对于简单构件的激光焊接,残余塑变理论可以用来预测变形,反变形法是控制焊接变形的有效方法。     

大型真空室焊接部件焊接变形预测与控制方法

真空室焊接部件在焊接过程中会产生较大的焊接变形,采用合理的焊接顺序及施加外部性约束可以在焊接过程中控制焊接变形. 根据固有应变理论给出了不同焊接接头固有应变的计算方法及应变在软件中的施加方法. 对真空室PS1段的四种焊接方案在无外部约束时的变形情况进行研究,根据无外部约束时PS1段的变形情况,确定了最优焊接顺序方案,制定了外部约束施加方法,并对有外部约束时PS1段的焊接变形进行计算. 结果表明,不同的焊接顺序其变形量不同,施加外部约束能够使焊接变形量明显减少,为实际加工生产提供了理论参考依据.     

搅拌摩擦焊对接面附近材料流变行为研究

搅拌摩擦焊(FSW)过程中的对接面附近工件材料流动变形行为与许多缺陷的形成密切相关。通过开展搅拌摩擦焊试验,研究对接面附近材料在FSW过程中的流动与变形行为。针对AA2024-T3铝合金进行研究,通过采用预制氧化膜为标示材料的方法进行标示,并采用不同的焊接参数进行FSW试验。结果表明,预制氧化膜在焊接过程中完全破碎,在焊缝中以氧化铝颗粒的形式呈有规律的“S线”分布,并且随着搅拌头转速的上升,宏观上“S线”分布宽度降低,局部上氧化铝颗粒尺寸越大,分布越紧密。标示材料在接头中的沉积特征体现出,在较低的搅拌头转速下,对接面附近工件材料在FSW过程中经历了剧烈的应变,而随着搅拌头转速的提高,总应变量反而减小。     

外部约束对薄壁高温合金尾喷管焊接变形的影响

以壁厚为1 mm的高温合金尾喷管为研究对象，基于热-弹-塑性有限元法与固有应变法，研究外部约束对薄壁高温合金尾喷管工件焊接变形的影响。通过焊接工艺试验和热-弹-塑性有限元法仿真，进行焊接热源校核，获得对接接头的固有应变和材料模型参数。建立全尺寸三维尾喷管焊接有限元模型，基于固有应变理论的弹性有限元方法，利用平板对接获得的材料模型参数，计算不同外部约束对尾喷管工件焊接变形的影响。结果表明：进气口约束对控制尾喷管焊后变形起主要作用，在进气口施加约束时，工件变形最小，为2.39 mm,变形发生在尾喷管内环与外环弧形焊缝位置。通过尾喷管组件产品焊后变形测量与仿真结果对照，验证了仿真计算方法的准确性，固有应变法可适用于薄壁尾喷管焊接变形预测。     

冲床机架焊接收缩量的预测

根据焊接接头经焊接热循环后的应变形成机理,研究了金属结构焊接变形的形成规律;建立了预测焊接变形的数学模型。本文归纳推导了焊缝纵向、横向收缩变形及其引起的角变形计算公式,综合考虑了焊接工艺参数、装配、焊接顺序、结构中的原始应力状态、散热、板厚、塑性区重叠等对焊接变形的影响;针对工程实际简化了机架焊接模型,同时对机架焊缝的纵向、横向变形及角变形进行了预测,计算结果与实测结果基本一致,精度满足工程实际要求。     

带热沉装置的搅拌摩擦焊研究

基于动态控制低应力无变形焊接法原理和搅拌摩擦焊特有的应力应变特点,设计开发了可应用于搅拌摩擦焊的单点式热沉和阵列式射流冲击热沉系统.通过两种不同热沉系统在铝合金搅拌摩擦焊中的对比研究,结果表明,单点式热沉虽然可以减小FSW焊接变形,但此种冷却方式会使接头性能大幅度下降,接头强度仅达到常规FSW的80%左右.经过改进的阵列式射流冲击热沉系统可以主动控制FSW过程中各个区域的温度分布,从而有效控制焊接过程的热弱塑性应力应变场,达到动态控制低应力无变形的焊接效果.焊缝氢含量的测试分析表明,阵列式射流冲击热沉系统可以改善接头的残余应力分布,防止冷却水侵入焊缝.带阵列式射流冲击热沉系统的搅拌摩擦焊技术可以实现低应力无变形焊接,且工艺适用性好,具有广阔的应用前景.     

基于等效载荷法的复杂结构焊接变形预测

采用固有应变等效载荷法,对复杂结构焊接变形进行预测.以焊接热过程产生的广义固有应变作为等效载荷,通过确定等效载荷的大小、加载区域和方式,编制等效载荷的施加程序,经过一次弹性有限元计算出焊接变形.以某51 000t散货船的双层底分段为例.采用等效载荷法对其焊接变形进行预测计算结果与实测数据进行比较,验证了固有应变等效载荷法预测船体双层底结构焊接变形的可行性,结果表明,固有应变法预测焊接变形结果与实测数据具有良好的一致性,且预测效率较高.     

基于固有应变理论的叉车门架焊接变形预测及控制

基于固有应变理论,建立了叉车门架的有限元模型并进行了数值模拟分析,求出叉车门架焊接变形大小及趋势,得出了对叉车门架焊接变形进行预测与控制的一种方法.该方法可推广应用于大型焊接件的焊接变形仿真、预测及改进指导焊接工艺.     

6061铝合金FSW接头与MIG焊接头对比试验

采用搅拌摩擦焊(FSW)和MIG焊分别对6061铝合金板进行了焊接试验,测试了焊接接头的强度,观察了焊接接头的金相组织,并进行了接头的硬度分布测试.结果表明,搅拌摩擦焊接头抗拉强度高达212.05 MPa,是母材抗拉强度的86％,比MIG焊的接头强度略高.焊接接头软化区宽度比MIG焊接头软化宽度窄.6061铝合金母材为典型的轧制组织,焊核区为细小的等轴晶组织,MIG焊接头焊缝为柱状晶组织.     

铝合金薄板焊件纵向塑性应变场的数值模拟

利用弹塑性有限元分析软件对普通焊件的纵向塑性应变场进行了模拟.结果表明,对于尺寸为200 mm×100 mm ×2 mm的2A12T4铝合金薄板填丝对接焊件,其焊缝部位只存在纵向拉伸塑性应变;在靠近焊缝的区域,既存在纵向压缩塑性应变,也存在纵向拉伸塑性应变;在焊缝长度方向纵向残余塑性应变的分布不均匀,在靠近起弧端和收弧端的区域呈现复杂的分布特征.焊接过程中温度场的变化和热源旁侧金属受力状况的不同是近缝区金属纵向塑性应变不均匀分布的原因.     

6063铝合金搅拌摩擦焊接头冲击断裂分析

以6063铝合金为主要研究对象，简要介绍了铝合金型材的搅拌摩擦焊接工艺及设备，研究了6063-T65l铝合金的冲击断裂性能、塑性变形能力及其搅拌摩擦焊接头的微观组织。研究表明，搅拌摩擦焊接头中为较细的再结晶组织，且强化相呈弥散分布，其冲击断裂性能和塑性变形能力与母材相近。     

Microstructure and Mechanical Properties of Dissimilar Double-Side Friction Stir Welds Between Medium-Thick 6061-T6 Aluminum and Pure Copper Plates

It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding. Thus, double-side friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates, and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed. It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min, while a nonuniform relatively thick intermetallic compound (IMC) layer is formed at the Al/Cu interface, resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass, and seriously deteriorates the mechanical properties of the joint. With the increase of welding speed to more than 300 mm/min void defects appear in the joint, but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface. The maximum tensile strength and elongation of Al/Cu weld are, respectively, 135.11 MPa and 6.06%, which is achieved at the welding speed of 400 mm/min. In addition, due to the influence of welding distortion of the first-pass weld, the second-pass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides. The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.     

Mechanical properties of friction stir welded Al alloys with different hardening mechanisms

The mechanical properties of precipitation hardened Al 6061-T651 and Al 7075-T6 and strain hardened Al 5083-H32, friction stir welded with various welding parameters, were examined in the present study. 4 mm thick Al 6061-T651, Al 7075-T6, and Al 5083-H32 alloy plates were used for friction stir welding (FSW) with rotating speed varied from 1000 to 2500 rpm (rotation per minute) and welding speed ranging from 0.1 to 0.4 mpm (m/min). Each alloy displayed slightly different trends with respect to the effect of different welding parameters on the tensile properties of the FSWed Al alloys. The tensile elongation of FSWed Al 6061-T651 and Al 7075-T6 tended to increase greatly, while the tensile strength decreased marginally, with increasing welding speed and/or decreasing rotating speed. The tensile strength and the tensile elongation of Al 6061-T651 decreased from 135 to 154 MPa and 10.6 to 17.0%, respectively, with increasing welding speed from 0.1 to 0.4 mpm at a rotating speed of 1,600 rpm. Unlike the age-hardened Al 6061-T651 and Al 7075-T6, the strain-hardened Al 5083-H32 showed no notable change in tensile property with varying welding parameters. The change in the strength level with different welding parameters for each alloy was not as significant as the variation in tensile elongation. It was believed that the tensile elongation of FSWed Al alloys with varying welding parameters was mainly determined by the coarse particle clustering. With respect to the change in tensile strength during friction stir welding, it is hypothesized that two competing mechanisms, recovery by friction and heat and strain hardening by plastic flow in the weld zone offset the effects of different welding parameters on the tensile strength level of FSWed Al alloys.     

Rupture locations of friction stir welded joints of AA2017-T351 and AA6061-T6 aluminum alloys

The tensile rupture locations of friction stir welded joints of AA2017-T351 and AA6061-T6 aluminum alloys were examined. The experiments show that the rupture locations of the joints are different for the two aluminum alloys, which are influenced by the welding parameters. When the joints are free of welding defects, the AA2017-T351 joints are ruptured in the weld nugget adjacent to the thermo-mechanically affected zone on the advancing side and the rupture surfaces appear as oval contours of the weld nugget, while the AA6061-T6 joints are ruptured in the heat affected zone on the retreating side and the rupture surfaces are inclined at a certain degree to the bottom surfaces of the joints. When welding defects are present in the joints, the AA2017-T351 joints are ruptured in the weld center, while the AA6061-T6 joints are ruptured on the retreating side near the weld center. The rupture locations of the joints are dependent on the internal structures of the joints and can be explained through them.     

Wavelet transform analysis of acoustic emission in monitoring friction stir welding of 6061 aluminum

In this paper, acoustic emission (AE) signals are detected and preliminarily analyzed in order to investigate the possibility of applying the AE technique for the in-process monitoring of an entire friction-stir-welding (FSW) process. Experimental tests are carried out using a high-speed rotating tool traversing on two, butted 6061 aluminum alloy plates with three equally spaced gaps made of two notches aligned along the butting joint of the parts. The wavelet transform (WT) is used to decompose the AE signal into various discrete series of sequences over different frequency bands. There are significant sudden changes in the band energy at the moment when the probe penetrates into and pulls out of the weld joint, as well as when the shoulder makes contact with or detaches from the plates. The band energy variation during the traversing of the tool over the defected region reflects the existence, location, and size of the weld defects. A three-dimensional representation of band energy vs time and scale gives valuable information on the potential weld defects during friction stir welding. Coupled with a contour mapping, the representation can be effectively utilized for monitoring the transient welding state and quickly identifying gap defects.     

温度峰值影响6061铝/AZ31B镁异种材料FSW接头成形的规律

以6061-T6铝合金与AZ31B镁合金为研究对象,基于Abaqus软件进行了异种材料搅拌摩擦焊过程的温度场数值模拟,重点分析搅拌针偏置镁侧下的搅拌区温度峰值影响焊缝表面成形的规律。结果表明,当焊接温度峰值高于Al-Mg共晶温度时,搅拌针根部附近区域会出现较明显的黏着现象,其随着焊接速度的降低而加剧,这与焊接温度峰值的升高相关。随着焊接速度的增加,焊缝表面更易避免裂纹缺陷的产生。当搅拌头的转速为1200r/min且焊接速度为40mm/min时,6061铝/AZ31B镁异种材料焊接接头的表面成形良好。     

Tensile properties of 6061-T6 friction stir welds and constitutive modelling in transverse and longitudinal orientations

Tensile stress–strain properties of Al alloy 6061-T6 (AA6061-T6) and its butt welds produced by the friction stir welding (FSW) process were characterized in two different loading orientations. AA6061-T6 FS welds were made under three sets of welding conditions. Micro-hardness tests were performed to investigate microstructural evolution during the FSW process. Flat tensile specimens were machined normal and parallel to the weld line. Transvers and longitudinal tensile tests were run on the base material (AA6061-T6) and its FS welds in an Instron testing machine. The strength and ductility (or fracture strain) of the FS welds observed in the transverse orientation were substantially less than those in the longitudinal orientation. Constitutive modelling of uniaxial tensile stress–strain behaviour in both orientations was presented using a rate-independent Ludwik equation. In addition, microstructures of the base material and its FS welds were examined with optical and transmission electron microscopy to discuss the decrease in the flow stress level and the increase in the strain hardening rate of the FS welds.     

Modeling friction stir welding process of aluminum alloys

The friction stir welding (FSW) process of aluminum alloys has been modeled using a two-dimensional Eulerian formulation. Velocity field and temperature distribution are strongly coupled and solved together using a standard finite element scheme. A scalar state variable for hardening is also integrated using a streamline integration method along streamlines. A viscoplastic constitutive equation to consider plastic flow and strength variations was implemented for the process modeling. Precipitates inside AA6061 alloys are sensitive to elevated temperatures and affect strength evolution with temperature. The overall effects of the precipitate variations with temperature on strength were reflected using temperature-dependent material parameters. The material parameters of constitutive equations were obtained from isothermal compression tests of various temperatures and strain rates. The effects of FSW process conditions on heating and hardening were investigated mainly near the tool pin. The microhardness distribution of the weld zone was compared with the prediction of strength. In addition, crystallographic texture evolutions were also predicted and compared with the experimental results.