Effectiveness of cold metal transfer process for welding 7075 aluminium alloys

Abstract

Cold metal transfer (CMT) welding is a promising process to improve the mechanical characteristics of the hard to weld 7075-T6 aluminium alloy owing to its unique advantages in contrast to conventional metal inert gas welding process. The welded joints, using ER5356, were identified and characterised by means of optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. Mechanical properties were measured by tensile and hardness tests. Results indicate that CMT provides better joint tensile strength and ductility compared to metal inert gas welding. The softness in the heat affected zone was very low, but a big hardness gap was recognised in the welded metal compared to base metal. The joint had mechanical property coefficients of 77%, 60% and 69% for yield strength, ultimate tensile strength and elongation respectively.     

超薄板MIG/MAG焊--CMT冷金属过渡技术

Fronius公司CMT（Cold Metal Transfer）冷金属过渡技术是在MIG／MAG焊基础上开发的一种革新技术．第一次将送丝运动与熔漓过渡过程进行数字化协调。当焊机的DSP处理器监测到一个熔滴短路信号。就会反馈给送丝机构,并回抽焊丝帮助溶滴脱落。使熔滴过渡在几乎无电流的状态下进行。整个焊接过程实现“热-冷-热”交替转换,每秒钟转换达70次。焊接热输入量大幅降低。实现0．3mm以上薄板的无飞溅、离质量MIG／MAG熔焊和MIG钎焊。更值得一提的是使用此种工艺还可进行只有激光和电了束才可实现的钢与铝的异种焊接。     

Effect of process parameters on the quality of aluminium alloy Al5Si deposits in wire and arc additive manufacturing using a cold metal transfer process

A 3D print device using a cold metal transfer arc welding station to melt a metallic filler wire is developed to build aluminium part by optimising the process parameters. First tests achieved using standard pre-recorded process parameters allow to study the effect of the travel speed and the average welding power on the geometrical characteristics of mono-layer deposits and on walls built by layers superposition. Finally, a parametric study of the effect of each process parameter controlling the shape of the arc current or voltage and the filler wire feeding is carried out in order to try to improve the geometrical regularity of the deposits, and to better understand the effect of each parameter on the melting of the filler wire, its transfer on the support plate, and the geometry of the formed bead.     

Indirect approaches for estimating the efficiency of the cold metal transfer welding process

In this work, two indirect approaches are compared to estimate the efficiency of the cold metal transfer welding process with two different current waveforms. The first approach is based on an analytical heat transfer model coupled with thermocouple measurements. The second method includes numerical heat transfer simulation of aluminium filler on the galvanised steel sheet. Then a diffusional-growth model allows evaluating the thickness of the Fe–Al intermetallic layer that was compared it to that of the experimental one. Results show that both methods give very similar process efficiencies. The process efficiency reaches a high value (0.92) with current waveforms using high-intensity pulses of short duration, whereas it decreases to 0.78 with current waveforms using low-intensity pulses of long duration.     

Al6061/TA2异种金属冷金属过渡焊接性分析

以AlSi₅ 焊丝对6061铝合金和TA2纯钛进行CMT熔钎焊,采用SEM,EDS分析焊接接头的微观组织特征,并通过拉伸试验对接头进行力学性能评定.结果表明,焊接过程稳定,焊缝成形美观.所得到的焊接接头具有熔焊和钎焊两部分,其中局部熔化的铝母材与熔融的焊丝混合后形成焊缝,焊缝金属与微熔的钛母材形成三个钎焊界面.钎焊界面主要成分为TiAl₃金属间化合物,其厚度较薄.此外,界面附近还有一些随机分布的棒状的TiAl₃金属间化合物.焊接过程中,随着焊丝偏移量的增加,焊缝力学性能提高.参数优化后的接头抗拉强度较高,且断裂在铝热影响区.     

SUS301L不锈钢冷金属过渡焊接接头焊接工艺、微观组织及力学性能

随着我国轨道交通行业的飞速发展,车体减重对于节省能源意义重大.采用CMT冷金属过渡焊接技术对4-0.8 mm SUS301L-MT不锈钢搭接接头进行了工艺研究,获得最优工艺参数;同时,对焊接接头进行了宏观形貌、微观组织观察、力学性能以及变形测量.结果表明,在最优工艺参数下,焊缝成形美观,无明显缺陷,焊缝区组织主要为奥氏体柱状晶和枝晶状铁素体;焊接接头拉伸剪切最大力达到了22 234.42 N,硬度测试最小值均出现在焊缝区;焊后试板呈现波浪变形,最大Z方向变形量出现在试板边缘.     

SUS 301L不锈钢冷金属过渡焊搭接接头焊接工艺、微观组织及力学性能

随着我国轨道交通行业的飞速发展,车体减重对于节省能源有着重大意义。利用CMT冷金属过渡焊接技术对4—0.8 mm SUS301L-MT不锈钢搭接接头进行工艺研究,获取最优工艺参数;同时,观察焊接接头的宏观形貌、微观组织,测量其力学性能及变形。结果表明,在最优工艺参数下,焊缝成形美观,无明显缺陷,焊缝区组织主要为奥氏体柱状晶和枝晶状铁素体;焊接接头最大拉伸剪切力达到22 234.42 N,硬度测试最小值均出现在焊缝区;此外,焊后试板呈现波浪变形,最大Z方向变形量出现在试板边缘。     

The effect of metal transfer stability (spattering) on fume generation,morphology and composition in short-circuit MAG welding

The main objective of this work was to evaluate the hypothesis that the greater transfer stability leads also to less volume of fumes. Using an Ar + 25%CO₂ blend as shielding gas and maintaining constant the average current, wire feed speed and welding speed, bead-on-plate welds were carried out with plain carbon steel solid wire. The welding voltage was scanned to progressively vary the transfer stability. Using two conditions of low stability and one with high stability, fume generation was evaluated by means of the AWS F1.2:2006 standard. The influence of these conditions on fume morphology and composition was also verified. A condition with greater transfer stability does not generate less fume quantity, despite the fact that this condition produces fewer spatters. Other factors such as short-circuit current, arcing time, droplet diameters and arc length are the likely governing factors, but in an interrelated way. Metal transfer stability does not influence either the composition or the size/morphology of fume particulates.     

汽车车身用铝合金冷金属过渡点塞焊工艺分析

采用AlSi₅铝合金焊丝,冷金属过渡方法对汽车车身用6061铝合金进行了搭接点塞焊试验,研究了送丝速度、铝板孔直径、点塞焊时间对点塞焊接头焊点直径、焊核直径和拉伸载荷的影响.结果表明,送丝速度主要影响焊点直径的大小,点塞焊时间和铝板孔直径主要影响焊核直径和拉伸载荷.接头拉伸载荷主要取决于焊核直径的大小,焊核直径越大,拉伸载荷越大,与焊点直径关系不大.接头为典型的熔焊接头,焊缝主要由α-Al固溶体和Al-Si共晶相组成,点塞焊接头断裂方式为撕裂型断裂.     

汽车用镁/钢异种金属冷金属过渡点焊工艺特性

采用冷金属过渡的方法对AZ31B变形镁合金和镀锌钢板进行搭接点焊试验,运用正交试验法优化工艺参数,同时利用光学显微镜、扫描电镜和万能拉伸试验机对焊接接头的微观组织和力学性能进行研究.结果表明,运用冷金属过渡方法能够获得成形美观和性能良好的焊接接头;工艺参数显著性顺序为镀锌钢板孔径大小、送丝速度、点焊时间;接头为典型的点熔钎焊接头,由钎焊结合区和熔焊结合区组成;接头的抗拉剪载荷可达3.12 kN,远大于相同尺寸下镁镁点焊试样的抗拉剪载荷,接头的断裂方式为剪切型断裂和撕裂型断裂.     

Development of Ag based brazing filler metal with low melting point

Abstract

This study was carried out to develop cadmium free silver based brazing filler metals that meet the following requirements. First, they have to have a melting point lower than that of BAg-1 brazing filler metal. Second, they have to have not only good wetting characteristics and the ability to produce a sound joint with excellent mechanical properties but also plastic formability. Using the calculated phase diagrams on Ag–Cu–Zn–Sn quaternary system alloys, the authors selected several alloys with a possibility of meeting the above requirements. The melting point and other properties, such as hardness and brazeability of the selected alloys, were evaluated. As a result, the authors successfully developed silver based brazing filler metals that have a low melting point below ～600°C and meet the above requirements by adding a small amount of indium as an alloying element into the Ag–Cu–Zn–Sn quaternary system alloy. The newly developed brazing filler metals are slightly inferior in wetting characteristics to BAg-1; however, the brazing filler metal containing ～3 mass-% indium element showed wetting characteristics comparable to those of BAg-1. Furthermore, the new brazing filler metals could produce joints with a high tensile strength equivalent to ～83% of that of a joint brazed using BAg-1.     

高强度低合金结构钢焊缝与母材的强度匹配研究

焊缝金属与母材的强度匹配系数是焊接接头力学性能非均匀参数之一，匹配方式不仅取决于焊缝金属和母材的名义强度，还取决于它们的分布形式和特征参数。试验和统计计算结果表明，12Ni3CrMoV钢和10Ni5CrMoV钢母材和焊缝金属的抗拉强度都服从正态分布。12Ni3CrMoV钢和其焊缝金属的强度匹配属于低强匹配，其低强、等强和超强匹配的概率分别为59.33%,37.03%和3.64%,低强匹配特征明显。10Ni5CrMoV钢和其焊缝金属的强度匹配属于等强匹配，其低强、等强和超强匹配概率分别为47%,48%和5%，其等强匹配分布比较明显。对应的两种钢的焊接接头，其超强匹配概率分别为3.64%和5%，在结构、焊接材料、工艺设计中值得注意。由于强度匹配系数的随机性，如何确定强度匹配系数，在什么范围内分别属于超强、等强、低强匹配，特别是等强匹配的界定方式应有别于低强和超强匹配，都是有特研究的问题。     

Controlled bridge transfer (CBT) gas metal arc process for steel sheets joining

In non-pulsed gas metal arc welding (GMAW), spatter can be reduced by lowering the short-circuit current to a low level just before the re-arcing. The reduction in spatter requires an improvement in the accuracy of predicting the re-arcing by stabilizing the metal transfer and improving the robustness of the accuracy against disturbances. The controlled bridge transfer (CBT) process optimizes the accuracy of predicting the re-arcing in real time in response to the metal transfer, realizes spatter reduction and stable arc in non-pulsed GMAW. Traditionally, GMAW is carried out using electrode positive polarity. However, this polarity is not sufficient for welding extra-thin steel sheets, specifically those thinner than 1.0 mm. With electrode negative (EN) CBT process, although slight arc voltage fluctuation occurs caused by the behaviour of cathode spots on the tip of the wire during EN polarity GMAW, instantaneous voltage uses command computation to improve the transient response against the disturbance. Consequently, a stable arc can be obtained without increasing the number of short circuits in a unit time to obtain spatter-free welds.     

Microstructure and mechanical properties of dissimilar joint between aluminum and aluminum-coated steel by cold metal transfer process

Two dissimilar materials, aluminum alloy and aluminum-coated steel, were joined by cold metal transfer process using AlSi₅ filler wire. To this end, the steel was coated with Al-Si. The steel did not melt and aluminum was melt to form the joint during the process, it was actually cold metal transfer welding-brazing. The macrostructure, microstructure, alloy element distribution, and inter-metallic compounds were analyzed by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. It was found that the Al-Si coating dissolved into the weld metal. The pre-existing thin Fe-Al-Si ternary inter-metallic compounds in the interface between the Al-Si coating layer and base metal steel also partially dissolved into the weld zone, tending to reduce the thickness of inter-metallic compounds. Approximate 3 μm thick undissolved inter-metallic compound was found at the interface after welding which could guarantee sound bonding strength in dissimilar materials joining. The sample was fractured at the fusion zone near the aluminum side in the tensile test. The ultimate tensile strength was about 156 MPa, and the fracture mode is ductile failure in nature according to its morphology.     

不同CMT工艺2014-T6焊缝成形及气孔分析

分别采用3种不同的冷金属过渡(CMT)焊接工艺进行2014-T6铝合金平板堆焊成形,研究不同CMT工艺对铝合金焊缝成形特征及气孔的影响. 结果表明,保持送丝速度7.5 m/min、电弧长度和保护气体纯Ar流量25L/min不变,2014-T6铝合金常规CMT焊缝具有明显的指状熔深特征,焊缝气孔缺陷严重且呈全焊缝分布特征;脉冲CMT(CMT-P)焊缝的指状熔深特征减缓,气孔显著减少,焊接速度0.6 m/min时焊缝基本无气孔;变极性复合脉冲CMT(CMT-PADV)焊缝熔深仅约0.4 mm,成形呈显著球形特征,气孔明显减少,焊接速度0.4 m/min时基本无气孔.     

数控自动编程中顺（逆）时针方向判别的数学建模及应用

在数控系统中，对顺（逆）时钟方向的判别是圆弧加工自动编程的关键技术之一，本文通过已知圆弧三点坐标值建立了顺（逆）时钟方向的判别的数学模型，并在FANUC-0TF数控系统的宏程序开发中成功地进行了应用，该数学模型具有效率高，通用性强的优点。     

激光-MIC复合焊工艺及其在轨道交通领域应用现状

阐述了激光-MIG复合焊接的基本原理和特点;介绍了铝合金激光-MIG复合焊接的工艺特性、研究现状及其在轨道交通车辆行业的工业应用.激光-MIG复合焊接充分集成激光焊接与MIG焊接的优点,能有效解决铝合金焊接的诸多问题,在轨道交通领域将会得到更加广泛的应用.     

An analysis of the cold spray process and its coatings

In this study, computational fluid dynamics (CFD) and extensive spray tests were performed for detailed analyses of the cold spray process. The modeling of the gas and particle flow field for different nozzle geometries and process parameters in correlation with the results of the experiments reveal that adhesion only occurs when the powder particles exceed a critical impact velocity that is specific to the spray material. For spherical copper powder with low oxygen content, the critical velocity was determined to be about 570 m/s. With nitrogen as the process gas and particle grain sizes from 5–25 μm, deposition efficiencies of more than 70% were achieved. The cold sprayed coatings show negligible porosity and oxygen contents comparable to the initial powder feedstock. Therefore, properties such as the electrical conductivity at room temperature correspond to those of the bulk material. The methods presented here can also be applied to develop strategies for cold spraying of other materials such as zinc, stainless steel, or nickel-based super-alloys.     

A contribution to the study of the cold wire TIG process in the flat,horizontal and overhead position with new torch designs and wire feed methodologies

This line of research aims to improve current procedures in the welding of boiler tubes, where manual welding processes are used and the quality of the welded joints depend exclusively on the welder’s skill. In this connection, what is proposed is to effect repairs with a more productive welding process called cold wire TIG with mechanized feed of cold wire, with the aim of achieving improvements in weldment quality and repeatability. The weld beads were assessed according to surface appearance, morphology, degree of dilution and convexity index. Tests were carried out with two wire guides (20° and 48°) for verifying the influence of the angle of introduction of the wire in the arc. The results indicate a considerable increase in productivity of the TIG process with mechanized wire feed, when the guide developed is employed with a wire entry angle of 20°, approaching the deposition rate obtained with the MIG/MAG process for the same wire diameter. Two configurations of wire feed could be tested: continuous and pulsed. The results showed that the pulsed wire feed configuration proposed was applied successfully in all positions, ensuring repeatability, process stability and stability of the molten pool.     

Determination of the metal/die interfacial heat transfer coefficient and its application in evaluating the pressure distribution inside the casting during the high pressure die casting process

Abstract

High pressure die casting (HPDC) experiments were conducted on a 650 t cold chamber die casting machine to study the interfacial heat transfer behaviour between casting and die. A 'step shape' casting and two commercial alloys namely ADC12 and AM50 were used during the experiments. Temperature and pressure measurements were made inside the die and at the die surface. The metal/die interfacial heat transfer coefficient (IHTC) was successfully determined based on the measured temperature inside the die by solving the inverse heat transfer problem. The IHTC was then used as the boundary condition to determine the 3-D temperature field inside the casting. Based on the predicted temperature distribution, the pressure distribution inside the casting was evaluated by assuming that the transferred pressure from the plunger tip of the injection side to the casting is primarily influenced by the solid fraction of the casting. Reasonable agreement was found between the determined pressure values and the measured pressures at the die surface of the casting.