Influence of shielding gas on the mechanical and metallurgical properties of DP-GMA-welded 5083-H321 aluminum alloy

In the present research, 6-mm-thick 5083-H321 aluminum alloy was joined by the double-pulsed gas metal arc welding （DP-GMAW） process. The objective was to investigate the influence of the shielding gas composition on the microstructure and properties of GMA welds. A macrostructural study indicated that the addition of nitrogen and oxygen to the argon shielding gas resulted in better weld penetration. Furthermore, the tensile strength and bending strength of the welds were improved when oxygen and nitrogen （at concentrations as high as approximately 0. 1vol%） were added to the shielding gas; however, these properties were adversely affected when the oxygen and nitrogen contents were increased further. This behavior was attributed to the formation of excessive brown and black oxide films on the bead surface, the formation of intermetallic compounds in the weld metal, and the formation of thicker oxide layers on the bead surface with increasing nitrogen and oxygen contents in the argon-based shielding gas. Analysis by energy-dispersive X-ray spectroscopy revealed that most of these compounds are nitrides or oxides.

Welding of nickel free high nitrogen stainless steel: Microstructure and mechanical properties

High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.

Analysis Microstructure of Weld Metal for HQ130+QJ63 High Strength Steel

The microstructure in the weld metals for HQ130 + QJ63 high strength steels,which are welded by Ar-CO_2 gas shielded metal arc welding,was analyzed by means of microscope and scan electron microscope(SEM).The relative content of different microstructure was evaluated with XQF-2000 micro-image analyzer.The effect of acicular ferrite content on the impact toughness was also studied.The test results indicated that the main microstructure in the weld metals of HQ130 + QJ63 high strength steels is acicular ferrite and a few pro-eutectic ferrite on the boundary of original austenite grain.Near the fusion zone there are columnar grains whose direction coefficient(X) is 3.22,but the microstructure in the center of the weld metal is isometric grain,whose direction coefficient X = 1.In order to avoid welding crack and improve welding technology the weld heat input should be strictly controlled in 10-16 kJ/cm.Thus,the main microstructure in the weld metals is fine acicular ferrite and the content of pro-eutectic ferrite is limited.The impact toughness in the weld metals of HQ130+ QJ63 steels can be ensured and can meet the requirements for application in engineering and machinery.

基于电弧力调控的CO2气体保护焊熔滴激振技术研究

基于能量最小原理采用Surface Evolver软件对CO_2气体保护焊熔滴形态进行了数值模拟,分析了不同尺寸的熔滴在不同焊接电流下的稳定熔滴形态,从理论上预测得出了CO_2气体保护焊在由大电流切换到小电流时,熔滴可由排斥状态转变为垂顺状态,甚至可以激发焊丝轴向的熔滴振荡。进而采用脉冲电流波形对此进行了试验验证,结果表明,将电流由峰值切换到基值,可以使熔滴由被托起状态转变为下垂状态,在熔滴较小、脉冲峰值较高且脉宽较小时,熔滴在峰值期间被轴向托起压缩没有径向排斥偏转,切换到基值后熔滴由排斥压缩状态回弹并开始较强烈的熔滴振荡,随着振幅衰减逐渐达到基值电流下的稳定形态。利用这一振荡将有助于实现CO_2气体保护焊稳定轴向自由无飞溅熔滴过渡的控制。

Effect of Welding Processes on Tensile and Impact Properties,Hardness and Microstructure of AISI 409M Ferritic Stainless Joints Fabricated by Duplex Stainless Steel Filler Metal

The effect of welding processes such as shielded metal arc welding, gas metal arc welding and gas tungsten arc welding on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade is studied. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the welded joints have been evaluated and the results are compared. From this investigatio.n, it is found that gas tungsten arc welded joints of ferritic stainless steel have superior tensile and impact properties compared with shielded metal arc and gas metal arc welded joints and this is mainly due to the presence of finer grains in fusion zone and heat affected zone.

焊接电参数的一种新型测试方法

为保证焊接过程的稳定性和焊接质量的可靠性,在焊接过程中对焊接电参数的监测十分必要.采用德国汉诺威大学"材料连接焊接工艺研究中心"开发的汉诺威焊接质量分析系统,对焊接过程电参数进行精确的统计分析,自动生成电弧电压、焊接电流概率密度分布曲线、电弧电压和焊接电流的波形图以及熔滴短路时间t1、电弧的燃弧时间t2、短路周期tC频数分布图,并且精确地得出相关数据.试验结果表明,汉诺威焊接质量分析系统能够对焊接工艺参数进行评估和优化,为科学评价焊接材料工艺性,提供了新的手段.

Effect of Tempering Temperature on Strength and Toughness of Novel Carbide-Free Bainite/Martensite Duplex Phase Steel

The microstructure in the weld metals for HQ130+QJ63 high strength steels, which are welded by Ar CO 2 gas shielded metal arc welding, was analyzed by means of microscope and scan electron microscope (SEM). The relative content of different microstructure was evaluated with XQF 2000 micro image analyzer. The effect of acicular ferrite content on the impact toughness was also studied. The test results indicated that the main microstructure in the weld metals of HQ130+QJ63 high strength steels is acicular ferrite and a few pro eutectic ferrite on the boundary of original austenite grain. Near the fusion zone there are columnar grains whose direction coefficient (X) is 3 22, but the microstructure in the center of the weld metal is isometric grain, whose direction coefficient X=1 In order to avoid welding crack and improve welding technology the weld heat input should be strictly controlled in 10-16 kJ/cm. Thus, the main microstructure in the weld metals is fine acicular ferrite and the content of pro eutectic ferrite is limited. The impact toughness in the weld metals of HQ130+QJ63 steels can be ensured and can meet the requirements for application in engineering and machinery.

船用铸钢件的焊接修补施工工艺探讨

在船舶改装及修理过程中,发现有大量的铸钢件在长期使用后出现裂纹,其中一些大型的铸钢件,若是进行换新将会增加成本,同时修理周期较长。这就要求船厂使用合理的焊接方法对裂纹进行修补并保证其实用性。文章从船用铸钢(ZG230-450)的焊接工艺、裂纹的修补、施工控制、试验结果比较等方面阐述了铸钢修补焊接的工艺要素及施工要点。