Dissimilar Arc Welding of Advanced High-Strength Car-Body Steel Sheets

A widespread usage of new advanced TWIP steel grades for the fabrication of car-body parts is conditional on the employment of appropriate welding methods, especially if dissimilar welding must be performed with other automotive steel grades. Therefore, the microstructural features and the mechanical response of dissimilar butt weld seams of TWIP and 22MnB5 steel sheets after metal-active-gas arc welding are examined. The microstructural and mechanical characterization of the welded joints was carried out by optical metallography, microhardness and tensile testing, and fractographic examination. The heat-affected zone on the TWIP side was fully austenitic and the only detectable effect was grain coarsening, while on the 22MnB5 side it exhibited newly formed martensite and tempered martensite. The welded tensile specimens exhibited a much larger deformation on the TWIP steel side than on the 22MnB5. The fracture generally occurred at the interface between the fusion zone and the heat-affected zones, with the fractures surfaces being predominantly ductile. The ultimate tensile strength of the butt joints was about 25% lower than that of the TWIP steel.     

焊接材料对Q550高强钢焊接接头组织的影响

根据Q550高强钢的焊接特点,研究了在不预热条件下ER50-6和MK·G60焊丝对Q550高强钢焊接接头显微组织的影响。结果表明,采用ER50-6焊丝焊接得到的焊缝组织为先共析铁素体、针状铁素体、珠光体和粒状贝氏体,熔合区断口有大量韧窝,表现为明显的韧性断裂特征;采用MK·G60焊丝的焊缝显微组织主要为贝氏体和大量的针状铁素体,接头熔合区断口形貌主要呈山谷状,具有准解理断口的特征,存在撕裂棱。     

非等厚异种钢电阻点焊焊点成形及神经网络预测

利用交流电阻点焊机在大量工艺试验的基础上,采用人工神经网络的方法,针对非等厚异种钢的双脉冲点焊构造了一种点焊焊点成形预测模型.该模型输入层由焊接电流、电极压力、通电时间和脉冲间隔组成,隐层为三节点双隐层,输出层包括熔核直径、熔核偏移量.通过试验,研究了输入层各焊接规范参数对焊点成形的影响,与神经网络预测结果对比表明,该模型预测结果与试验结果有较好的一致性,建立的模型较为可靠.     

搅拌头形状对铝合金搅拌摩擦点焊流场的影响

采用商用CFD软件包中的FLUENT软件对2A14铝合金搅拌摩擦点焊过程中材料的流动情况进行了三维数值摸拟.为分析搅拌头轴肩底面轮廓对材料流动的影响,分别建立了平面轴肩和凹面轴肩.当采用凹面轴肩时,材料流动状况更明显.为分析搅拌针的形状对点焊稳态过程流场的影响,建立了圆柱形、三角形和方形三种不同形状的搅拌针模型.与圆柱形搅拌针相比,三角形和方形搅拌针引起的材料流动的范围更大.本文在计算过程中,没有考虑热耗散.     

不锈钢的电阻点焊

对不同厚度及种类冷轧和热轧不锈钢进行了点焊性能试验,重点探讨了马氏体、铁素体不锈钢的点焊可焊性,从微观金相组织和接头硬度分布的两个角度分析了马氏体、铁素体不锈钢的点焊过程,并经大量试验提出了提高马氏体、铁素体不锈钢点焊接头抗剪强度的有效方法。     

弹簧钢电阻点焊

分析了弹簧钢电阻点焊接头常见缺陷类型，形貌，成因及危害，提出通过采用增大电极压力，调制焊接电流脉冲和随机多脉冲回火热处理等工艺措施，可获得优质点焊接头，这就为钢质弹性件的以焊代铆指出方向。     

基于人工神经网络的船舶高强钢焊接变形分析预测

以新型船舶高强钢为主要对象 ,在物理模拟试验和有限元分析基础上 ,通过人工神经网络建立船舶分段钢结构焊接变形数值模拟模型 ,仿真焊接工艺参数、板材厚度、焊接顺序等因素对船体钢结构变形的影响 ,探索抑制船舶高强钢焊接变形的有效途径。仿真结果表明 ,在各种因素中组焊顺序是影响焊接变形的主要因素 ,通过选择小电流同向分段退焊工艺将有效抑制船体分段钢结构焊接过程中产生的变形 ;采用上述方式建立的模型可以快速预测、预报船舶高强钢焊接过程中产生的变形量 ,为新型船舶研制、生产提供真正的理论指导 ,避免焊接试验的盲目性     

Three-Dimensional Visualization of Material Flow During Friction Stir Welding of Steel and Aluminum

Material flow is a key phenomenon to obtain sound joints by friction stir welding (FSW), and it is highly dependent of the welded material. It is well known that the optimal FSW condition depends on the welded material. However, the material flow during FSW has not been totally clarified in spite of many researches. Especially, the material flow of steel during FSW is still unclear. It seems difficult to understand the material flow by the traditional method such as the tracer method or observation of the microstructure in the stir zone. Therefore, in this study, the material flow of steel was three dimensionally visualized by x-ray radiography using two pairs of x-ray transmission real-time imaging systems, and was then compared with the material flow of aluminum. The result revealed the effect of the welded material on the material flow during FSW.     

声阻尼复合钢板的电阻点焊

为使复合钢板得到更广泛地使用,需要对材料在电阻点焊过程中的行为有一个基本的了解。     

Material Flow Tracking for Various Tool Geometries During the Friction Stir Spot Welding Process

This study applied powder-tracing techniques to mount Cu and W powders on A6061-T6 aluminum sheets to investigate the material flow mechanism of friction stir spot welding (FSSW) using various geometric tools. The experimental results showed that the geometry of the tools plays a crucial role and determines the entrances of material flow during FSSW. It was believed that instantaneous voids were filled up with material flow in all directions for triangular pins, and the voids were located at the pin bottom for cylindrical pins. In accordance with the plastic rule of material flow, the pressure gradient is the necessary condition to cause material flow during FSSW; therefore, the transient constraint space (TCS) is required to generate pressure in this space. Enlargement of the TCS accompanies the evolution of the stir zone (SZ). A generated void causes a steep pressure gradient, which is regarded as the entrance of material flow. A tool with screw threads causes downward driving force, which determines the intermixing behavior between the upper and lower sheets, and also affects the size of the SZs.     

基于超级电容的超薄不锈钢板储能点焊焊机研制

对厚度仅为0.1mm的超薄304不锈钢板进行点焊时,其焊点焊接所需焊接能量要求控制精确,否则很容易造成烧穿或焊不上,很难达到预期的焊接质量要求。鉴此,提出了基于超级电容的储能焊焊机的研制。通过分析超级电容器原理及其模型,得出了将其应用于储能点焊的理论依据。根据储能电容组的电压与储能能量之间是平方关系,储能电容组的容值与储能能量之间为比例关系,在焊接板材超薄的情况下,提出了调节电容组容量的大小来调节焊接能量的方法。根据电阻点焊过程中动态电阻的变化规律对放电回路的电流进行控制,这样可较好地解决焊接规范较硬的问题。     

Microscopic Deformation in Individual Grains in an Advanced High-Strength Steel

In situ synchrotron microbeam x-ray diffraction experiments were carried out to study the microscopic deformation within individual ferrite grains in a martensite/ferrite dual-phase steel (DP980) under incremental tensile loading. The differential aperture x-ray microscopy technique was used to resolve the strain variations as a function of depth up to 100 μm deep from the sample surface. The highly inhomogeneous distributions of the lattice strain, which is associated with the elastic deformation and stresses inside the grains, were determined by means of monochromatic energy diffraction, whereas insights to the plastic deformation were revealed by polychromatic energy diffraction.     

异质材料铁-镍点焊熔合过程的研究

对异质材料铁-镍点焊在不同规范下熔合过程进行了试验研究，包括可焊性及规范参数的选择。分析了铁-镍点焊时出现的各种缺陷及消除或改善方法、熔核组织特点与规范的关系。对异质金属焊接时出现的旋流，指出了成因及消除方法。     

Structural Transformations Occurring upon Explosive Welding of Alloy Steel and High-Strength Titanium

Features of the structure of a layered material welded by explosion of high-strength titanium alloy and tool roller steel with an intermediate layer of the structural low-carbon steel have been studied. The structural transformations occurring in materials upon their dynamic interaction have been analyzed. Particular attention is paid to the structure of vortex zones formed at the interfaces of billets of various steels, as well as structural steel and titanium-based alloy. The structural analysis methods made it possible to fix stable and metastable joints appearing upon the explosive welding of various metals. To reveal features of structural transformations caused by prolonged heating, billets of titanium alloy and structural steel were also joined by diffusion welding. It has been shown that, in the course of the diffusion welding process, a continuous layer of stable brittle intermetallic compounds is formed along the entire interface of the welded materials. In the explosively welded materials, the intermetallic phases are distributed locally and, thus, they have a weaker embrittlement effect.     

The Mechanical Behavior of Friction-Stir Spot Welded Aluminum Alloys

Aluminum and alloys are widely used in the automotive industry due to the light weight, good formability, and malleability. Spot welding is the most commonly used joining method of these materials, but the high current requirements and the inconsistent quality of the final welds make this process unsuitable. An alternative welding technique, the friction-stir spot welding process, can also be successfully used in joining of aluminum and alloys. In this study, 1-mm-thick AA5754 Al-alloy plates in the H-111 temper conditions were joined by friction-stir spot welding using two different weld parameters such as tool rotational speed and dwell time. Mechanical properties of the joints were obtained with extensive hardness measurements and tensile shear tests. The effect of these parameters on the failure modes of welded joints was also determined.     

Modeling of AA5083 Material-Microstructure Evolution During Butt Friction-Stir Welding

A concise yet a fairly comprehensive overview of the friction stir welding (FSW) process is provided. This is followed by a computational investigation in which FSW behavior of a prototypical solution-strengthened and strain-hardened aluminum alloy, AA5083-H131, is modeled using a fully coupled thermo-mechanical finite-element procedure developed in our prior study. Particular attention is given to proper modeling of the welding work-piece material behavior during the FSW process. Specifically, competition and interactions between plastic-deformation and dynamic-recrystallization processes are considered to properly account for the material-microstructure evolution in the weld nugget zone. The results showed that with proper modeling of the material behavior under high-temperature/severe-plastic-deformation conditions, significantly improved agreement can be attained between the computed and measured post-FSW residual-stress and material-strength distribution results.     

汽车车身钢板电阻点焊焊接参数模型研究

汽车车身板材电阻点焊焊接参数目前缺乏有效的数学模型可借鉴,只能基于经验,并通过大量的试验获得一些零散的、非系统性的经验数据来最终确认,需要消耗大量人力、物力和时间.本文以汽车车身钢板电阻点焊为研究对象,通过构建焊点合理的物理和数学模型,利用材料的物理属性,对影响点焊质量的关键焊接参数进行深入研究.在等效板厚概念的基础上...     

低合金高强钢表面不锈钢带极堆焊的研究

采用不锈钢带极双层堆焊,在低合金高强钢表面堆焊不锈钢耐蚀层。研究了过渡层、表面层带极成分对堆焊层的成分、组织及堆焊层δ铁素体含量的影响,并对堆焊试样进行横向侧弯和纵向侧弯测试。结果表明:过渡层采用309L、表面层采用347L宽50 mm带极,在焊接电流700~850 A、焊接速度140~160 mm/min条件下,可获得与低合金高强钢基体结合良好的堆焊层,堆焊层的增碳层无明显M脆化倾向,堆焊层组织为均匀的奥氏体+δ铁素体双相组织,δ铁素体含量在4.5%~5.5%之间,奥氏体晶粒明显细化。     

Microcrack Formation During Gas Metal Arc Welding of High-Strength Fine-Grained Structural Steel

The recent development of high-performance-modified spray arc processes in gas metal arc welding due to modern digital control technology and inverter power sources enables a focused spray arc,which results in higher penetration depths and welding speed.However,microcracks occurred in the weld metal while approaching the process limits of the modified spray arc,represented by a 20-mm double layer DV-groove butt-weld.These cracks were detected in structural steel exhibiting a yield strength level of up to 960 MPa and are neither dependent on the used weld power source nor a consequence of the modified spray arc process itself.The metallographic and fractographic investigations of the rather exceptional fracture surface lead to the classification of the microcracks as hot cracks.The effects of certain welding parameters on the crack probability are clarified using a statistical design of experiment.However,these microcracks do not impact the design specification for toughness in the Charpy V-notch test(absorbed energy at —40 ℃ for the present material is 30 J).