Effect of variable polarity frequency on 2A14-T6 aluminum alloy welds using HPVP-GTAW process

Hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） for 2A14-T6 high strength aluminum alloy was carried out and the effects of variable polarity frequency with constant pulse current frequency 40 kHz on weld bead geometry, microstrueture and microhardness were analyzed. Experimental results indicate that, compared to that of the conventional VP-GTAW process, the weld depth and ratio of weld depth to width are improved significantly by the variable polarity frequency in the HPVP-GTAW process, which the ratio of weld depth to width is improved by 36% at equal variable polarity frequency of 100 Hz, and improved by 55% with that of 200 Hz. Weld microstructure and microhardness distribution are changed obviously with the increase of variable polarity frequency. In the conventional VP-GTA W process, the grains in weld central zone are coarser, and the microhardness in weld central zone and fusion zone is about 95 HV and the lowest 82 HV, respectively. The microhardness is enhanced to a certain extent both in the weld central zone and fusion zone with the variation of variable polarity frequency in the HPVP-GTAW process due to the refinement and uniformity of weld microstructure. With the variable polarity frequency of 600 Hz, the microhardness in weld central zone and fusion zone reaches nearly 110 HV and 97 HV, respectively.     

Microstructure and grain boundary engineering of a novel Fe-Cr-Ni alloy weldment made with self-developed composition-matched weld filler metal

The microstructure, texture, and yield strength of an advanced heat-resistant alloy weldment made with composition-matched weld filler were investigated. Scanning electron microscopy, energy dispersive spectroscopy, and electron backscatter diffraction were used to characterize the microstructural and textural changes. Various grain boundary engineering (GBE) processes were performed on the weldment. The yield strengths of the weldment at 973 K were obtained before and after GBE processing, and were mostly consistent with the theoretically predicted values. The coincident-site lattices, misorientation, and recrystallization of the weld metal after GBE were analyzed, and the results indicate that the increase in dislocation density and the improvement in special grain boundaries in the weld metal are the main reasons for the yield strength elevation of the weldment after GBE. The variation in elongation after high-temperature tests has the same tendency as that in the impact toughness with different GBE parameters, which is related to the coarsening behavior of carbides.     

氮含量对含Ti-Nb的X70管线钢焊接热影响区组织及冲击韧性的影响

采用中频真空感应炉冶炼了两种不同N含量的X70管线钢。利用Gleeble-2000热模拟研究了两种钢焊接热影响区的组织及冲击性能。采用三丝埋弧焊对两种钢分别进行了焊接,随后采用光学显微镜和冲击试验研究了两种钢的焊接接头组织及冲击韧性。结果表明:在N含量高的钢中发现了尺寸为20~50 nm、弥散分布的(Ti,Nb)(C,N)粒子,而N含量低的钢中只存在少量尺寸为50~100 nm的(Ti,Nb)(C,N)粒子。细小、弥散的(Ti,Nb)(C,N)粒子抑制了晶粒的长大,细化了晶粒,对稳定试验钢的热影响区冲击韧性有利。     

基于X射线计算机辅助成像技术的带料管道焊缝检测

采用便携式数字CR系统对某大型石化企业的400条压力管道进行了X射线计算机辅助成像检测(CR)。通过设置管道是否带料、采用不同射线源和是否考虑介质对透照的影响等三种情况的比对试验,验证了检测手段的可靠性及有效性。现场检测能发现管道对接焊缝的未焊透、未熔合、夹渣、气孔和裂纹等典型缺陷,并针对CR现场应用存在的一些问题进行了讨论,为CR技术在带料管道焊缝检测中的广泛应用奠定基础。     

基于改进卷积神经网络的管焊缝X射线图像缺陷识别方法

针对卷积神经网络(CNN)应用于焊缝探伤图像识别时,目标区域占比小,局部信息冗余,激活函数小于零时出现硬饱和区导致模型对输入变化较敏感、网络参数难以训练的问题,采用超像素分割算法(SLIC)和改进的ELU激活函数构建CNN模型进行焊缝探伤图像缺陷识别. 首先,在CNN模型中使用ELU激活函数,在缓解梯度消失时对输入噪声产生更好的鲁棒性,同时,利用SLIC算法对图像像素进行像素块处理的特点,增大焊缝探伤图像中感兴趣区域的占比,降低局部冗余信息,提高模型在训练过程中的特征提取能力. 通过对焊缝探伤图像感兴趣区域提取并与所述CNN模型进行对比试验. 结果表明,该方法在焊缝探伤图像特征提取、训练耗时及识别准确率方面较传统卷积神经网络有更好的表现.     

超声作用阶段及形式对熔池晶粒结晶的影响

理解不同超声作用下的熔池晶粒结晶特点对超声辅助TIG焊接工艺的优化具有重要意义. 以铝锂合金为研究对象,改变超声作用阶段及施加形式,分析焊缝晶粒分布特征. 结果表明,电弧熄灭后超声作用下,焊缝边缘为断裂的柱状晶,焊缝中心为等轴晶;熄弧前及熄弧后均有超声作用时,焊缝内部全部为等轴晶. 持续超声形式和瞬态超声形式对熔池晶粒结晶具有不同的作用,持续超声主要促进熔池内晶粒的异质形核而促使等轴晶形成,瞬态超声主要通过破碎枝晶细化晶粒. 超声细化铝锂合金TIG焊缝晶粒机制与超声作用阶段及形式具有直接联系.     

低温分离容器的制造

以醇烃液三相分离器为例,对低温分离容器的制造过程中材料的采购、检验、制造、焊接、热处理等关键工序和制造难点进行了详细阐述和分析。     

双丝窄间隙GMAW三元保护气成分对焊缝成形的影响

窄间隙焊接在厚板焊接中有着较大的优势,保护气成分在一定程度上影响电弧行为及熔滴过渡,进而影响焊缝成形。针对30 mm厚Q235低碳钢,研究了窄间隙坡口下Ar,He和CO2构成的三元保护气中,不同的保护气成分比例对焊缝成形的影响。结果表明：固定的He含量为5%,当CO2含量为10%时得到的焊缝表面成形良好,指状熔深相对较小,侧壁熔深相对较大的焊缝。固定CO2含量为10%,当He含量为10%时得到的焊缝表面成形良好,指状熔深相对较小,侧壁熔深相对较大的焊缝。     

新型高强塑积富B-Al合金的电阻点焊熔核飞溅研究

通过自行设计配比一种新型高强塑积富B-Al合金材料。考虑到该种合金材料主要用于乘用车结构件,因此着重研究电阻点焊焊接性。同时借鉴国际焊接性评判标准ISO 14327-2004,设计了复杂焊接条件下的混合水平均匀设计实验。找出了影响该材料点焊熔核飞溅的主要工况因素,并通过建立点焊熔核飞溅边界曲线,从而有效地预测该材料点焊飞溅概率,更进一步地了解点焊熔核质量及点焊飞溅现象与焊接工艺、焊接环境等因素的相互关系,通过建立该材料点焊熔核力矩平衡方程与熔核膨胀应力数值仿真,深入分析点焊飞溅机理,在一定程度上促进了该新型高强塑积合金的实际应用。     

矩形型腔熔体充填规律的可视化实验

通过精密注射成型可视化实验系统,直观地研究3种典型矩形型腔内高温熔体在型腔中的流动行为,研究得到矩形型腔内制品熔接痕和喷射缺陷形成机理.通过分析模具结构设计、成型工艺参数与熔体宏观流动行为及制品宏观缺陷之间的内在联系,提出解决熔接痕和喷射缺陷的具体措施.