Microstructure and Mechanical Properties of Pulse MIG Welded 6061/A356 Aluminum Alloy Dissimilar Butt Joints

The microstructure and mechanical properties of pulse metal inert-gas(MIG) welded dissimilar joints between 4 mm thick wrought 6061-T6 and cast A356-T6 aluminum alloy plates were investigated. The tensile strength of the joints reached 235 MPa, which is 83% of that of 6061 aluminum alloy, and then decreased with the increase of travel speed while keeping other welding parameters constant. The microstructure, composition and fractography of joints were examined by the optical microscopy(OM),scanning electron microscopy(SEM) and electron probe microanalysis(EPMA). Grain boundary liquation and segregation occurred in the partially melted zone(PMZ) on 6061 aluminum alloy side, and brittle Fe-rich phases were observed in partially melted zone on A356 aluminum alloy side. The minimum microhardness appeared in heat-affected zone(HAZ) near A356 aluminum alloy substrate. The samples during tensile test failed mainly in PMZ and HAZ on A356 aluminum alloy side through mixed fracture mode with quasi cleavage and dimples on fracture surface.     

交流MIG焊电弧稳定性控制

为解决直流ＭＩＧ焊电弧的磁偏吹问题，研制了交流ＭＩＧ焊电源。介绍针对交流ＭＩＧ焊的主要问题－电弧稳定性所开展的工作。前后采用４种弧过零点的控制方案，经过实验取得了与直流ＭＩＧ焊接近的电弧稳定性。指出交流ＭＩＧ电弧稳定性与换向前的电流，换向后的电压有密切关系。     

Systematic study of effect of cross-drafts and nozzle diameter on shield gas coverage in MIG welding

Abstract

A shield gas flowrate of 15–20 L min^?1 is typically specified in metal inert gas welding, but is often adjusted to as high as 36 L min^?1 by welders in practice. Not only is this overuse of shield gas wasteful, but uncontrolled high gas flows can lead to significant turbulence induced porosity in the final weld. There is therefore a need to understand and control the minimum shield gas flowrate used in practical welding where cross-drafts may affect the coverage. Very low gas coverage or no shielding leads to porosity and spatter development in the weld region. A systematic study is reported of the weld quality achieved for a range of shield gas flowrates, cross-draft speeds and nozzle diameters using optical visualisation and numerical modelling to determine the shield gas coverage. As a consequence of the study, the shield gas flow has been reduced to 12 L min^?1 in production welding, representing a significant process cost saving and reduced environmental impact with no compromise to the final weld quality.     

Comparison of four arc welding processes used for aluminium alloy cladding

Abstract

Metal inert gas (MIG), pulsed MIG, cold metal transfer MIG (CMT) and tungsten inert gas (TIG) welding processes were employed to produce clads. The cladding operations were analysed by an infrared thermal imaging technique and beads were characterised by X-ray radiography, neutron diffraction and microhardness mapping. Surprisingly, the CMT process produces the highest temperatures, but also the highest cooling rate. The MIG processes produce more residual stress and defect than TIG process.     

Effect of welding sequence on residual stress and deformation of 6061-T6 aluminium alloy automobile component

Four different welding sequences of double-pulse MIG welding were conducted for 6061-T6 aluminum alloy automobile bumpers by using nonlinear elastoplasticity finite element method based on ABAQUS software. The post-welding residual stress and deformation were definitely different among the four welding sequences. The results showed that the highest temperature in Solution A was approximately 200 °C higher than the melting point of base metal. High residual stress was resulted from this large temperature gradient and mainly concentrated on the welding vicinity between beam and crash box. The welding deformation primarily occurred in both of the contraction of two-ends of the beam and the self-contraction of crash box. Compared with other welding sequences, the residual stress in Solution A was the smallest, whereas the welding deformation was the largest. However, the optimal sequence was Solution B because of the effective reduction of residual stress and good assembly requirements.     

Role of welding process energy on the microstructural variations in a cobalt base superalloy hardfacing

Cobalt base superalloy hardfacings have been deposited by manual arc welding. Such deposits of total thickness 15 to 17 mm are realised in four successive layers on a steel substrate. The aim of this study is to analyse the role of the welding energy on hardfacings microstructural variations.Microstructure of these hardfacings is formed of a mixture of eutectic precipitates between primary dendrites of a cobalt-rich fcc phase. The high resulting dilution with the substrate induced by such manual arc welding process generates a chemical gradient in the deposit thickness able to involve various carbides volume fraction: the eutectic precipitates volume fraction varies in the reverse order of dilution with no significant difference versus welding energy. On the other hand, the fact of producing hardfacing in successive layers causes a secondary precipitation. In other terms, this kind of deposit involving high temperatures for a sufficient long time makes the dendritic Cr and Co-rich zones precipitate. Thus, fine cuboids particles of Cr₂₃C₆ carbides are formed in the dendrites. In accordance with higher welding energy used, the higher temperatures reached generate the Cr₂₃C₆ carbides size increasing.     

热轧常化焊接机组结构及控制系统的优化

在热轧常化机组中,焊机设备处于非常重要的地位。通过对氩弧焊机机械结构和PLC控制系统的改进,提高了带钢对中和焊接间隙控制精度,保证了带钢卷板焊接质量,保障热轧常化机组现场生产的正常运行。     

铝合金三丝双脉冲MIG焊熔滴过渡及电信号分析

文中搭建了三丝双脉冲MIG焊系统,采用高速摄像电信号同步采集系统对焊接过程进行实时监测,研究了铝合金三丝双脉冲MIG焊熔滴过渡行为以及双脉冲频率对焊缝成形的影响. 结果表明,弱脉冲向强脉冲过渡时,熔滴过渡表现为一脉一滴;强脉冲向弱脉冲过渡时,在开始阶段,焊丝发生再引燃,在结束阶段,熔滴过渡表现为两脉一滴;双脉冲频率增加,焊缝鱼鳞纹变密,双脉冲频率为3 Hz时,鱼鳞纹疏密均匀,焊缝成形最佳.     

6N01铝合金水冷MIG焊接头组织和性能

针对6N01铝合金熔化焊接头软化问题,研究了水冷对MIG焊接头组织和性能的影响,并与自然冷却条件下接头进行对比.金相试验结果表明,水冷使填充和盖面焊道部分熔化区变窄,焊缝近熔合线的柱状晶区变宽,焊缝内部等轴晶细化;显微硬度试验结果表明水冷条件下接头软化区范围明显变窄且硬度提高;软化区TEM观察显示水冷减少了β'析出相长大;水冷还提高了MIG焊接接头屈服强度和抗拉强度.结果表明,水冷能优化6N01铝合金MIG接头组织并提高力学性能.     

管道MIG焊双通道电弧声信号采集与特征分析

对管道MIG焊双通道信号采集和特征分析做了初步研究．因管道其内部是一个相对狭小密闭的空间,回声的干扰相对较大,经过对采集的双通道电弧声信号进行ICA信号分离,对分离后的信号做小波降噪处理,信噪比得到明显提高．对降噪后的信号从时域、频域和时频域角度,综合分析管内和管外电弧声信号与焊缝熔透状态之间的内在相关性,发现电弧声信号能量及其频谱特性与熔透状态高度相关,焊接过程中信号能量幅值随熔透增大而增大,为后续利用电弧声信号来控制焊接质量提供了基础．