Investigation on the deposition rate and the dilution ratio of plasma surface welding

A new kind of plasma technology with both high deposition rate and low dilution ratio was developed under the calculation and analysis of the arc flame characteristics of plasma arc,the kinematics behavior of powder and powder's heating in the arc. Compared with normal plasma surfacing method, the idea using constricting nozzle with small orifice diameter, long plasma arc and increasing the distance from meeting point of the two beams of powder to workpiece, to achieve the goals of high deposition rate and low dilution ratio, was put forward here. In order to prove this idea, a set of experimental system was built up and obtained satisfied results including high deposition rate(more than 25 kg/h )and low dilution ratio(less than 5%). The success of this study offers a promising prospect for developing the powder plasma surface welding in China and may open a way to improve this technology further in efficiency and quality.

Effect of welding process methods on the regularity of iron element in copper/steel deposited layer

Copper was surfaced on the Q235 substrate by shielded metal arc welding （SMAW） and tungsten inert-gas （TIG） arc welding, the regularity of iron element in deposited metal was analyzed by metallograph, scanning electron microscopy and energy disperse spectroscopy. The results indicate that with the increase of SMA W welding speed, the iron content decreases and the granular or spherical iron becomes more bulky in the overlay. The iron content obviously decreases with the increase of surfacing layers＇ numbers in multilayer welding because of the substrate dilution. On the third layer, the microstrueture of deposited metal is single-phase e-copper. Under the influence of welding methods, the granular or spherical crystal morphology is more likely to form in SMAW for the more divergent arc heat, but is dendrite in TIG welding because of centralized arc energy.

Characteristic of laser-MIG hybrid welding with filling additional cold wire for aluminum alloy

The weld appearance, deposition rate, welding efficiency, stability of arc, laser keyhole characteristic, and weld property were studied by using a novel laser-MIG hybrid welding process with filling wire of aluminum alloy. The results were also compared with those by conventional laser-MIG hybrid welding process. It was found that with the suitable process parameters this novel welding process for aluminum alloy was stable and final weld bead had fine appearance. Compared to conventional laser-MIG hybrid welding process, during this novel welding process the stability of arc, the laser keyhole characteristic and the weld property were similar, while the keyhole cycle frequency and keyhole opening area had differences of 1.23% and 15.34%, respectively, and the welding efficiency increased by about 31% without increasing heat input.

A study on consumable aided tungsten indirect arc welding

A consumable aided tungsten indirect arc welding method has been studied. This method is different from the traditional TIG welding because it introduces an MIG welding torch into the traditional TIG welding system. An indirect arc is generated between the consumable electrode of the MlG welding torch and the tungsten electrode of the TIG welding torch, but not generated between the tungsten electrode of the welding torch and the base metal. Welding current flows from the consumable electrode to the tungsten electrode in the free-burning indirect are. The consumable aided tungsten indirect arc welding not only rapidly melts the welding wire but also effectively restrains the excessive fusion of the base metal. The welding experiment and the theoretical analysis confirm that this method can obtain a high deposition rate and a low dilution ratio during the welding process.

Underwater Laser Welding/Cladding for High-performance Repair of Marine Metal Materials:A Review

With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must be performed in underwater environments.The underwater laser welding/cladding technique is a promising and advanced technique which could be widely applied to the maintenance of the damaged equipment.The present review paper aims to present a critical analysis and engineering overview of the underwater laser welding/cladding technique.First,we elaborated recent advances and key issues of drainage nozzles all over the world.Next,we presented the underwater laser processing and microstructural-mechanical behavior of repaired marine materials.Then,the newly developed powder-feeding based and wire-feeding based underwater laser direct metal deposition techniques were reviewed.The differences between the convection,conduction,and the metallurgical kinetics in the melt pools during underwater laser direct metal deposition and in-air laser direct metal deposition were illustrated.After that,several challenges that need to be overcame to achieve the full potential of the underwater laser welding/cladding technique are proposed.Finally,suggestions for future directions to aid the development of underwater laser welding/cladding technology and underwater metallurgical theory are provided.The present review will not only enrich the knowledge in the underwater repair technology,but also provide important guidance for the potential applications of the technology on the marine engineering.

Narrow gap space contributes to chemical metallurgy of self-shielded arc welding

The slag-free self-shielded flux-cored wire was fabricated to apply for the narrow gap welding.The results showed that narrow gap welding shows lower welding spatter compared with hardfacing except under voltage of 30 V and current of 260 A.The deposition efficiency keeps over 90%for both 12 mm and 8 mm narrow gap welding.For 12 mm narrow gap welding,when the voltage is 28 V and the current is 264 A(or 286 A),no pores are found in the narrow gap weld.In the continuous welding process,manganese vapor,aluminum vapor and CO continuously generate to form gasbag and occupy the narrow gap space,thus protecting the droplet and molten pool from the invasion of air.

Influence of welding parameters on nitrogen content in welding metal of 32Mn-7Cr-1Mo-0.3N austenitic steel

The transfer behavior of nitrogen into the welding metal during gas tungsten arc welding process of 32Mn-7Cr-1Mo-0.3N steel was investigated. The effects of gas tungsten arc welding process variables, such as the volume fraction of nitrogen in shielding gas, arc holding time and arc current on the nitrogen content in the welding metal were also evaluated. The results show that the volume fraction of nitrogen in gas mixture plays a major role in controlling the nitrogen content in the welding metal. It seems that there exhibits a maximum nitrogen content (depending) on the arc current and arc holding time. The optimum volume fraction of nitrogen in shielding gas is 4% or so. The role of gas tungsten arc welding processing parameters in controlling the transfer of nitrogen is further (confirmed) by the experimental results of gas tungsten arc welding process with feeding metal.

Gas metal arc welding of duplex stainless clad steel plates

The 2205 duplex stainless ＋ DH36 clad steel plate was welded by gas metal arc welding（GMAW）, and the welding performance of the clad steel plate was investigated. The results show that the adaptability of the welding procedure for the base metal of carbon steel, the transition layer, and the cladding material is excellent. The test results indicate that the phase proportion and component dilution of the GMAW-welded joints of clad steel plate can be effectively controlled to yield joints with good mechanical properties and corrosion resistance.

Tool-workpiece interaction and shear layer flow during friction stir welding of aluminium alloys

Material flow phenomena during friction stir welding(FSW) and the forming mechanism of "onion rings" are complicated and currently not fully understood. In the present FSW study aluminium alloys 5083 and A356,with the latter more readily welded than the former,were used. The experiments were conducted to obtain samples of tool and workpiece "frozen" together during FSW for analysis. Two deposition modes for forming the weld nugget zone were observed,one for each alloy with the present FSW parameters. The first is the deposition of shear layers forming the "onion rings" in 5083 alloy nugget. The tool-workpiece interaction leading to the layer thickness being equal to the ratio of welding speed and tool rotation speed is suggested. The second mode is the combination of depositing the rotational shear material in the lower part on the advancing side and the drag flow of material from the retreating site forming the rest of the A356 nugget. The latter mode resulted in the absence of a clear ring structure.

Influence of Tacking Sequence on Residual Stress and Distortion of Single Sided Fillet Submerged Arc Welded Joint

Submerged arc welding （SAW） is advantageous for joining high thickness materials in large structure due to high material deposition rate. The non-uniform heating and cooling generates the thermal stresses and subsequently the residual stresses and distortion. The longitudinal and transverse residual stresses and angular distortion are generally measured in large panel structure of submerged arc welded fillet joints. Hence, the objective of this present work is to quantify the amount of residual stress and distortion in and around the weld joint due to positioning of stiffeners tack. The tacking sequence influences the level of residual stress and proper controlling of tacking sequences is required to minimize the stress. In present study, an elasto-plastic material behavior is considered to develop the thermo mechanical model which predicts the residual stress and angular distortion with varying tacking sequences. The simulated result reveals that the tacking sequence heavily influences the residual stress and deformation pattern of the single sided fillet joint. The finite element based numerical model is calibrated by comparing the experimental data from published literature. Henceforth, the angular distortions are measured from an in-house developed experimental set-up. A fair agreement between the predicted and experimental results indicates the robustness of the developed numerical model. However, the most significant conclusion from present study states that tack weld position should be placed opposite to the fillet weld side to minimize the residual stress.

Optimization of the Deposition Rate of Tungsten Inert Gas Mild Steel Using Response Surface Methodology

In welding, so many factors contribute to good quality welds. The deposition rate is the rate of weld metal deposit at fusion zone during welding, which also is a key factors affecting the quality of welded joints. Too high or low deposition rate compromises the integrity of weld. This study was carried out with the aim of providing an approach for producing better weldments by optimizing and predicting deposition rate of low carbon steel using Response Surface Methodology (RSM). 30 sets of experiments were done, adopting the central composite experimental design. The tungsten inert gas welding equipment was used to produce the welded joints. Argon gas was supplied to the welding process to shield the weld from atmospheric interference. Mild steel coupons measuring 60 × 40 × 10 mm was used for the experiments. The results obtained show that the voltage and current have very strong influence on the deposition rate. The models developed possess a variance inflation factor of 1. And P-value is less than 0.05, indicating that the model is significant. The models also possessed a high goodness of fit with R2 (Coefficient of determination) values of 91%. The model produced numerically obtained optimal solution of current of 160.00 Amp, voltage of 20 volts and a gas flow rate of 17 L/min produces a welded material having deposition rate of 0.4637 kg/hr. This solution was selected by design expert as the optimal solution with a desirability value of 98.8%. A weld simulation using the optimum value obtained produced a weld with good quality.

高效多丝熔化极气体保护焊(GMAW)工艺的研究现状及进展

随着全球制造业竞争的日益激烈,我国提出了“中国制造2025”制造强国战略,其重点发展的十大领域中,与焊接技术密切相关的就高达八个,不仅极大地推动了焊接技术的革新发展,而且对焊接效率和质量均提出了更高的要求。由于熔化极气体保护焊(Gas metal arc welding,GMAW)易于实现自动化焊接,具有生产效率高、焊接质量好及位置适应性好等优点,所以广泛应用于机械制造业中。实现高效GMAW的主要途径有提高焊接速度以及焊接熔敷率。针对以上两种途径,国内外焊接工作者在双丝GMAW的基础上,引入了第三根甚至多根焊丝,研发了各种多丝GMAW工艺。本文针对国内外研发的各类多丝GMAW工艺进行了分析,重点介绍了多丝GMAW工艺的焊接原理、工艺特点及其应用,通过上述分析对各类多丝GMAW工艺进行归纳总结,并进一步展望了多丝焊接的发展方向,即多丝GMAW工艺亟需在电弧物理理论、设备开发和新焊材研发等方面展开深入的研究工作。

Sc对ER5356焊丝接头组织与性能的影响

分别以Al-Mg和Al-Mg-Sc焊丝作为填充材料,采用MIG焊接工艺对20 mm厚7A52铝合金板进行对接焊。分析了Sc对接头显微组织、力学性能、孔隙率的影响。结果表明:Sc的添加使熔敷金属的抗拉强度和断后伸长率分别提高了3.1%和9.1%,使其横截面的气孔率下降了66.4%;焊接接头抗拉强度和断后伸长率分别提高了3.5%和1.6%,拉伸断裂机制为韧性断裂。此外,Sc的添加细化了熔敷金属和焊缝的晶粒;使焊缝边缘组织的柱状晶的轴比降低;并在熔合区生成Al_(3)Sc粒子,成为MgZn_(2)的形核点,促进Zn向熔合区扩散。

Influence of carbon content on microstructure and mechanical properties of 1000 MPa deposited metal by gas metal arc welding

The effects of carbon content (0.078-0.100 wt.%) on the microstructure and properties of 1000 MPa grade deposited metal produced by gas metal arc welding have been investigated. Experimental results show that the microstructure of the deposited metal was mainly composed of martensite, bainite and retained austenite. With increasing carbon content, the proportion of martensite increased, and the amount of bainite was reduced. High carbon content is beneficial to strength, but harmful to impact toughness, and thus, carbon reductions lead to the increase in impact toughness. When the carbon content was 0.100 wt.%, the lowest Charpy absorbed energy of 47 J at — 40℃ for the deposited metal was achieved, the highest yield strength of 1038 MPa was attained, and the yield-to-tensile ratio was more than 0.88, while the highest Charpy absorbed energy of 55.7 J at — 40℃ and the lowest yield strength of 915 MPa were obtained when the deposited metal contains 0.078 wt.% C, and the yield-to-tensile ratio was less than 0.85. It is concluded that bainite fraction and fine effective grain size were the dominant factors to achieve good comprehensive mechanical properties (the required strength and an acceptable toughness) of deposited metals with various carbon contents.

热处理温度对1000 MPa级高强钢熔敷金属组织和性能的作用机制

采用丝级埋弧焊方法制备1000 MPa级高强钢熔敷金属,利用SEM、EBSD、XRD和TEM等微观分析方法研究了焊后热处理温度(500~620℃)对1000 MPa级高强钢熔敷金属组织演变的影响,并通过拉伸和冲击试验评估其力学性能.结果表明,随着热处理温度升高,1000 MPa级高强钢熔敷金属抗拉强度和屈服强度对比焊态(as welded,AW)先升高后降低,熔敷金属热处理后比AW韧性降低.1000 MPa级高强钢熔敷金属在540℃热处理时获得较好强韧匹配效果,抗拉强度1030MPa,屈服强度970 MPa,-40℃冲击韧性58 J.1000 MPa级高强钢熔敷金属在500~620℃热处理过程中M/A组元中的A逐渐分解为碳化物和铁素体,M在620℃热处理时生成逆转变奥氏体并保留至室温.碳化物对于位错具有钉扎作用,但随热处理温度升高碳化物对位错的钉扎作用减弱,位错通过滑移和攀移不断减少.熔敷金属析出的碳化物对位错的钉扎作用强于位错滑移的软化作用时,熔敷金属强度提高,碳化物对位错的钉扎作用弱于位错滑移的软化作用时基体组织软化,熔敷金属强度降低.析出的碳化物导致位错塞积,产生的应力集中区域成为裂纹源,使热处理态熔敷金属韧性低于AW.

Mn含量对ENiCrMo-2镍基焊条熔敷金属组织和性能的影响

采用焊条电弧焊方法制备了ENiCrMo-2镍基焊条合金熔敷金属。采用光学显微镜(OM)、扫描电子显微镜(SEM)以及能谱分析(EDS)方法对熔敷金属的晶界形貌、析出相成分、析出相形貌特征加以研究;对熔敷金属进行拉伸试验并分析断口形貌,研究了Mn含量对熔敷金属组织及力学性能的影响。结果表明,显微组织以奥氏体柱状晶为主,Mn含量的提高改变了偏析带宽度,但对析出相的影响并不明显。析出相包括富Cr碳化物(M_(7)C_(3))以及富Mo、Cr碳化物(M_(23)C_(6)),部分析出物为M7C3包裹着M_(23)C_(6);随着Mn含量从0.16 wt.%升高到0.91 wt.%,熔敷金属的塑韧性和抗裂性得到提高,熔敷金属力学性能良好。通过断口分析发现,当Mn含量为0.16 wt.%时,存在较弱的结晶裂纹和高温失塑裂纹倾向,Mn含量的提高使裂纹倾向减弱,沿晶开裂的断裂面上的韧窝形貌逐渐均匀变深。因此,适当增加Mn含量可优化ENiCrMo-2镍基焊条合金熔敷金属的组织和力学性能,当Mn含量增加至0.91 wt.%时熔敷金属的力学性能最优。

存放时间对铝合金焊丝熔敷金属及焊接性能的影响

针对已开封的铝合金焊丝,对其存放期限进行研究。分别选取存放时间为0、24 h、48 h、72 h、168 h、360 h的焊丝进行熔敷金属抗气孔性能试验和力学性能试验,并测试焊接接头疲劳性能,探究存放时间对铝合金焊丝性能的影响。研究结果表明:存放时间在0~360 h,熔敷金属的抗气孔性能均可以满足标准要求,熔敷金属的气孔数与存放时间呈线性递增关系,拟合度R 2因子达0.94;熔敷金属的力学性能均可以满足标准要求;随着存放时间的增加,熔敷金属的σb、σ0.2、断后延伸率A没有显现出特定的变化规律;随着存放时间的增加,焊接接头疲劳极限σ-1呈现出下降的趋势,存放时间0~24 h,焊接接头疲劳性能良好,承受动载荷能力较强;从实际应用的角度上讲,存放时间0~360 h的铝合金焊丝可以用于生产承受静载荷的构件,而对于承受动载荷的关键构件,焊接所用铝合金焊丝的存放时间不宜超过24 h。

无熔深熔覆铜工艺

针对钢表面熔覆纯铜层 ,提出了感应、电弧、连续炉和熔铸“熔覆铜”的工艺方法。SEM组织分析检测表明 ,这些工艺实现了钢基体与熔覆层的无熔深焊接 ,熔覆层与钢基体有良好的冶金结合 ,界面无未焊合、夹渣等缺陷。力学性能试验表明 ,焊接界面结合剪切强度超过了熔覆层的强度。EDAX面、线扫描和成分分析表明 ,钢基体未发生熔化 ,基体与铜熔覆层的过渡区域宽仅几十微米 ,熔覆层中基体成分含量小于 1%

双钨极氩弧焊工艺及焊缝成形机理分析

针对3 mm和4 mm厚度低碳钢板,对双钨极氩弧焊的焊接工艺进行了研究。与常规钨极氩弧焊的对比分析表明,由于双钨极氩弧焊降低了电弧压力,提高了焊丝的熔敷率,因而在大电流高速度焊接时,极大地减少了凹坑、咬边等缺陷,实现了良好的焊缝成形,从而改善了常规钨极氩弧焊不适合大电流高速度焊接的不足,拓宽了钨极氩弧焊的使用范围,提高了焊接生产率。此外,在焊接试验的基础上,进一步对双钨极氩弧焊降低电弧压力、减少焊接缺陷的机理进行了分析。