Effect of Postweld Aging Treatment on Fatigue Behavior of Pulsed Current Welded AA7075 Aluminum Alloy Joints

This article reports the effect of postweld aging treatment on fatigue behavior of pulsed current welded AA 7075 aluminum alloy joints. AA7075 aluminum alloy (Al-Zn-Mg-Cu alloy) has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers, and railway transport systems. The preferred welding processes of AA7075 aluminum alloy are frequently gas tungsten arc welding (GTAW) process and gas metal arc welding (GMAW) process due to their comparatively easier applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique. Rolled plates of 10 mm thickness have been used as the base material for preparing multipass welded joints. Single V butt joint configuration has been prepared for joining the plates. The filler metal used for joining the plates is AA 5356 (Al-5Mg (wt.%)) grade aluminum alloy. Four different welding techniques have been used to fabricate the joints and they are: (i) continuous current GTAW (CCGTAW), (ii) pulsed current GTAW (PCGTAW), (iii) continuous current GMAW (CCGMAW), and (iv) pulsed current GMAW (PCGMAW) processes. Argon (99.99% pure) has been used as the shielding gas. Rotary bending fatigue testing machine has been used to evaluate fatigue behavior of the welded joints. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. Grain refinement is accompanied by an increase in fatigue life and endurance limit. Simple postweld aging treatment applied to the joints is found to be beneficial to enhance the fatigue performance of the welded joints.     

Effect of chemical composition on anode area formation in TIG arc welding. Effect of chemical composition on weldability in fabrication in high alloyed steel (1st Report)

Summary

This paper describes a fundamental investigation of the weldability of A5052 wrought alloy and AC7A castings in electron beam welding and gas tungsten arc welding. Microscopic observations, hardness, tensile, and impact tests were used. In electron beam welding, the tensile and impact properties of the wrought alloy weld metal and heat affected zone are satisfactory. Micro-solidification cracks are found in the weld metal, whereas micro-liquation cracks are found in the AC7A HAZ. The tensile properties of the welds produced by GTAW (or TIG) are virtually equivalent or slightly inferior to those of the electron beam welded joints.     

Joining dispersion-strengthened,rapidly solidified,P/M Al alloys

The weldability of dispersion-strengthened, rapidly solidified Al-Fe alloys is limited by the residual hydrogen content, solidification behavior, and the high-temperature deformation behavior of these alloys. Consequently, the selection and application of welding processes and conditions to join these aluminum alloys—either to themselves or with other engineering alloys—must be based on the ability of the welding process conditions to eliminate or minimize the occurrence of fusion zone porosity; “recreate” a microstructure similar to the rapidly solidified, powder metallurgy base alloy; and/or “retain” the superior base alloy microstructure in the weld zone. Toward this end, an understanding of the physical metallurgy and high-temperature deformation characteristics of the dispersion-strengthened, rapidly solidified, powder metallurgy Al-Fe alloys and the effects of welding process conditions and parameters on weld solidification behavior and microstructural development in the weld zone will enable one to optimize welding conditions to obtain desirable combinations of weld microstructure and mechanical properties.     

Gas tungsten arc welding studies on similar and dissimilar combinations of Al-Zn-Mg alloy RDE 40 and Al-Li alloy 1441

Abstract

The present study is concerned with gas tungsten arc welding of two high strength aluminium alloys, namely, an Al-Zn-Mg alloy (RDE 40) and an Al-Li based alloy of Russian grade 1441. One of the critical requirements of these two alloys is that they should be weldable. In the present work, weldability aspects of these alloys were studied in terms of solidification cracking tendency, microstructure, tensile properties, and microhardness across the welds. These studies were extended to dissimilar welds between RDE 40 and 1441 produced via conventional gas tungsten arc (GTA) welding as well as pulsed current GTA welding. It was found that RDE 40 welds were less sensitive to solidification cracking and weld metal porosity compared with 1441 alloy. The superior weldability of RDE 40 was related to the equiaxed nature of the fusion zone and a lower sensitivity to moisture pickup. It was possible to produce RDE 40-1441 welds without defects. Pulsed current welding of RDE 40 to 1441 showed improved mechanical properties compared with conventional GTA welding, and these were related to the refinement of the fusion zone microstructure.     

Effect of heat input and filler metals on weld strength of gas tungsten arc welding of AISI 316 weldments

The present work investigates the effect of filler metals and heat input on weld bead geometry and mechanical properties of alloy316 welded by using GTAW.ER309 L,ER316 L and ERNi Cr Mo-3 filler metals,are applied to study their effect on the weldment.Weld defects are examined using radiographic testing.The mechanical properties of welds are evaluated through uniaxial testing,hardness measuring,and bending test.The mechanical properties and cooling rate decrease with increasing heat input.Tensile strength,yield stress and percentage elongation of weldments using three fillers are determined.Best results are obtained using ERNi Cr Mo-3.Besides,weld nugget area,cooling time and solidification time increases with increasing heat input.Finally,applying bending test on weld samples,cracks,tearing and surface defects are not observed.     

Search for filler metal for welding of ferrous alloys to titanium

Abstract

The use of a filler metal to facilitate the gas tungsten arc (GTA) welding of ferrous alloys to titanium alloys has been investigated. Semi-empirical rules have been applied to identify alloying elements that would resolve the important problems of brittle intermetallic formation and weld cracking. Vanadium was found appropriate. The GTA welds between a low carbon steel and Ti–15V–3Cr–3Sn–3Al made with a vanadium filler wire resisted cracking better than comparable autogenous welds. However, the presence of a hard, brittle eutectic microconstituent along the ferrous side of the fusion boundary drastically limited the gain in weldability. As anticipated, analysis of GTA welds produced with vanadium filler wire suggested the presence of a ternary (Fe,Ti,V) single phase. Although cracking was reduced with vanadium, the practical benefit of a vanadium filler wire for GTA welding is small because the weld metals remain very hard and brittle.     

Enhancing the weldability of CP titanium friction stir welds with elemental foils

ABSTRACT

Friction stir welding (FSW) has proven to be a viable technique for joining a wide variety of alloys. However, thick section welding of alpha and near-alpha Ti alloys has proven particularly challenging. Previous research at the Naval Research Laboratory using Ni markers in CP Ti friction stir welds indicated that elemental additions of Ni to the joint line can provide substantial benefits for improved weldability of these alloys. The current study surveys the effects of Ni and other elemental additions to CP Ti friction stir welds to determine their influence on the resultant weld microstructure, weld surface finish, and welding machine forces. These results reveal that Ni provides the most benefits for the concentrations examined, but other elements may also provide benefits at lower concentrations. The addition of these elements may improve the weldability and weld quality for FSW of CP Ti, enabling thick section welding of this and similar alloys.     

Fe_3Al合金与A304钢的TIG焊试验研究

采用TIG焊方法,分别选择9Cr-1Mo钢焊丝、A347焊丝和Inconel82Ni基合金焊丝作填充材料对Fe3Al合金与A304不锈钢进行焊接试验,并对接头质量进行了检测分析。结果表明:三种填充焊丝的焊缝中均有裂纹产生,并且在Fe3Al合金的热影响区还出现了微裂纹;采用Cr-Mo钢焊丝时,溶池金属沿Fe3Al母材基体结晶长大,接头区组织较均匀,而采用Ni基焊丝时,Fe3Al侧存在界线明显的熔合区。     

Effects of base and filler chemistry and weld techniques on equiaxed zone formation in Al–Zn–Mg alloy welds

Abstract

Equiaxed zone (EQZ) formation in Al–Zn–Mg alloy welds as affected by base metal, filler metal chemistry and weld techniques is studied. Filler metal chemistry and welding techniques have great influence on the formation of EQZ microstructure as base metal composition has. In an effort to characterise the equiaxed grain zone formation in Al–Zn–Mg alloy welds two commercial Al alloys AA7018 and RDE40 were selected. Gas tungsten arc welding in continuous current, pulsed current and arc oscillation mode were applied to weld the base materials. The influence of Sc containing fillers have been studied and compared with the commercial filler material. Mechanical and metallurgical characterisation were carried out in the EQZ. Intergranular corrosion in EQZ was studied according to ASTM G 110-92. Results reveals that RDE40 with low solute contents showed wider EQZ but relatively better corrosion and mechanical properties compared to AA7018 EQZ. Gas tungsten arc welding in pulsed and arc oscillation mode fusion boundary region exhibits better corrosion and mechanical properties compared to continuous current mode welds. Addition of Sc to the AA5556 filler combined with pulsed mode resulted in elimination of EQZ, better corrosion and mechanical properties compared to welds made with conventional AA5556 filler and also the presence of Sc within the EQZ so called unmixed zone has been observed.     

Fe3Al合金与A304钢的TIG焊试验研究

采用TIG焊方法，分别选择9Cr-1Mo钢焊丝、A347焊丝和Inconel82Ni基合金焊丝作填充材料对Fe3Al合金与A304不锈钢进行焊接试验，并对接头质量进行了检测分析。结果表明：三种填充焊丝的焊缝中均有裂纹产生，并且在Fe3Al合金的热影响区还出现了微裂纹；采用Cr—Mo钢焊丝时，溶池金属沿FeAl母材基体结晶长大，接头区组织较均匀，而采用Ni基焊丝时，Fe3Al侧存在界线明显的熔合区。     

Laser welding of high-strength aluminium–lithium alloys with a filler wire

The possibilities of using laser welding with a filler wire for joining sheet materials made of V-1469 and V-1461 high-strength aluminium–lithium alloys are investigated. The optimum conditions of placing the filler wire in relation to the laser beam in the weld pool are determined. The optimum welding parameters resulting in the high-quality formation of the welded joint with equal sagging and excess metal and the absence of porosity and cracks are also determined. The mechanical properties of welded joints are outlined and the microstructure of the welded joint is investigated. The corrosion resistance of the produced welded joints is studied.     

254SMO/Q235B异种钢焊接接头显微组织

分别选用ERNiCrMo-2,ERNiCrMo-3,ERNiCrMo-10,ERNiCrMo-12,ERNiCrMo-13及ERNiCrMo-14 6种镍基合金焊丝,采用手工TIG焊对254SMO/Q235B异种钢板进行焊接试验解决254SMO波纹管与Q235B钢管焊接时出现的裂纹问题,.焊后利用光学显微镜、X射线衍射仪、扫描电子显微镜和能谱仪对焊接接头进行了分析研究.发现采用ERNiCrMo-2,ERNiCrMo-3和ERNiCrMo-14焊丝时,焊缝中有较多的微裂纹出现;选用另外3种焊丝进行焊接时,焊缝成形良好,未出现焊接裂纹.结果表明,该焊接裂纹为热裂纹,异种钢物理性能的差异及焊缝中杂质元素的偏析是造成焊接裂纹的关键因素.     

Influence of scandium on weldability of 7010 aluminium alloy

Abstract

The commercial 7000 series aluminium alloys are based on medium strength Al–Zn–Mg and high strength Al–Zn–Mg–Cu systems. The medium strength alloys are weldable, whereas the high strength alloys are non-weldable. This is because the amount of copper present in these alloys gives rise to hot cracking during solidification of welds. As a result, the high strength Al–Zn–Mg– Cu base alloys are not used for applications where joining of components by welding is an essential step. In the present study, using a combination of qualitative Houldcroft test and quantitative Varestraint test, it is shown that a small addition of scandium to the commercial 7010 alloy reduces the hot cracking susceptibility during solidification of welds produced by the gas tungsten arc welding process. The improvement in weldability is found to be the result of the considerable grain refinement in the weld structure following the scandium addition. The results of microhardness and tensile tests are further described within the context of the present work to demonstrate that the 7010+Sc welds also exhibit a combination of improved strength and ductility.     

Characterisation of solidification cracking in pulsed Nd:YAG laser welding of 2024 aluminium alloy

Abstract

Aluminium alloy AA2024 is one of the most susceptible alloys to solidification cracking. The influence of Nd:YAG laser welding parameters on cracking severity of AA 2024 alloy was studied. Welding was performed in two modes: single spot welding and overlap spot welding. In single spot welding mode, the formation of columnar zone increases cracking severity in the fusion zone. In overlap spot welding mode, the solidification cracks were characterised as: cracks propagated from previous spot, cracks initiated from the fusion line with the previous spot, and cracks initiated from the fusion line with the base metal. It was established that in comparison there is very limited tendency for initiation of new cracks from the fusion line with the weld metal of a previous spot.     

Microcracking in multipass weld metal of alloy 690 Part 3 – Prevention of microcracking in reheated weld metal by addition of La to filler metal

Abstract

The effect of addition of La to a filler metal on microcracking (ductility dip cracking) in the multipass weld metal of alloy 690 was investigated with the aim of improving its microcracking susceptibility. The susceptibility to ductility dip cracking in the reheated weld metal could be greatly improved by adding 0·01–0·02 wt-%La to the weld metal. Conversely, excessive La addition to the weld metal led to liquation and solidification cracking in the weld metal. Hot ductility of the weld metal at the cracking temperature was greatly improved by adding 0·01–0·02 wt-%La to the weld metal, implying that the ductility dip cracking susceptibility was decreased as a result of the desegregation of impurity elements of P and S to grain boundaries due to the scavenging effect of La. The liquation and solidification cracking resulting from excessive addition of La to the weld metal is attributed to the formation of liquefiable Ni–La intermetallic compound. A multipass welding test confirmed that microcracks in the multipass weldment were completely prevented by using a filler metal containing an addition of 0·01 wt-%La.     

新型电阻塞焊连接方法分析

使用一种新型的"电阻塞焊"连接方法焊接7075铝合金搭接接头. "电阻塞焊"的工艺过程是先在两板材搭接部分的中心位置打一个孔,将圆柱填充物压入,最后用电阻点焊的方法将填充物与板材焊在一起.该工艺方法旨在保持点焊原有优点的同时,提高其强度等接头性能.研究分析了该新方法的工艺、形核过程、力学性能以及微观组织,并对比研究了同参数下电阻点焊试件的接头性能.结果表明,采用新型电阻塞焊方法的接头在强度等力学性能方面优于同参数下的电阻点焊试件,同时焊点处的裂纹等缺陷也较少,接头的综合性能更为优良.     

Study and prevention of cracking during weld-repair of heat-resistant cast steels

Heat-resistant cast steels are highly sensitive to cracking as they are weld-repaired because of their very low ductility. To prevent weld-repair cracking of three different heat-resistant cast steels used for the manufacturing of superplastic forming (SPF) dies, the effect of various welding parameters, such as the choice of the filler material, the number of weld passes and the pre-heating temperature has been investigated. The choice of an appropriate filler metal and the pre-heating to 400 °C of the material prior to welding drastically lower the propensity to cracking, but remain unable to eliminate cracks entirely. To further reduce weld-repair cracking and hopefully prevent it completely, a buttering technique has been developed. Buttering of the base metal surface with nickel alloys before weld-repair has been shown to prevent cracking of the base metal, but results in some hot-cracking of the buttering layer itself. On the other hand, buttering with Ni–Fe alloys, less sensitive to hot-cracking, results in crack-free weld-repairs.     

2090Ce铝锂合金的焊缝热裂纹敏感性及接头力学性能

采用焊缝合金化手段，通过设计新型焊丝向焊缝中添加Ｌｉ、Ｚｒ和Ｃｅ等合金化元素，研究了２０９０Ｃｅ稀土铝锂合金焊缝金属的热裂纹敏感性；探讨了合金元素对接头力学性能的影响及作用规律；进而研究了适用于焊接２０９０Ｃｅ合金的焊丝合金成分。试验结果表明，向焊缝金属中添加适量的合金元素Ｌｉ、Ｚｒ和Ｃｅ，能够细化晶粒；增加焊缝中的共晶数量并改善其分布形态，从而有助于降低焊缝金属的热裂纹敏感性。另外，适量的Ｌｉ、Ｚｒ和Ｃｅ等合金元素还能够在不降低接头塑性的同时，明显改善接头的强度；但Ｌｉ和Ｃｅ含量过多则会对接头性能，特别是塑性造成损害。所设计的焊丝材料能够适用于焊接２０９０Ｃｅ稀土铝锂合金。     

薄片状TiNi合金/不锈钢激光微焊接接头组织特征

采用微型脉冲激光对0.2 mm厚的薄片状TiNi形状记忆合金/不锈钢异种材料进行对接焊,研究了接头的微观组织特征。结果表明,以纯Ni丝为填充材料、以微型脉冲激光为热源可以实现TiNi合金/不锈钢异种材料的良好焊接。焊缝中心区为细小的等轴晶组织,主要元素为Ti、Ni、Fe。Ti元素的含量和不锈钢母材基本接近, Ni元素的含量略高于TiNi合金母材,远高于不锈钢母材,但TiNi合金母材一侧基本没有Fe元素。TiNi合金母材与焊缝之间存在明显的界面区,宽度为10～20 μm,界面区有从不锈钢母材扩散而来的Fe、Cr元素。不锈钢母材与焊缝之间界面区的宽度较小,表现为界面线     

Microstructure and Mechanical Behavior in Dissimilar SAF 2205/API X52 Welded Pipes

The welding of a duplex stainless steel SAF 2205 DSS(UNS 31803) and high strength low alloy steel API X52 by shielded metal arc welding process was conducted using two different filler metals,the duplex E2209 and austenitic E309 grade.The microstructures of the dissimilar metal joints have been investigated by optical microscopy,scanning electron microscopy,energy-dispersive spectroscopy(EDS) and X-ray diffraction.EDS analysis at the interface X52 weld metal showed an evident gradient variation of Cr and Ni between boundaries of fusion and type II,where the highest hardness value was recorded.Tensile strength and toughness values of the weld metal produced by E309 electrode are slightly higher than those of the weld metal produced by E2209 electrode.Potentiodynamic polarization tests of different regions of the welded joints evaluated in 3.5%NaCl solution exhibit a high corrosion resistance of both weld metals.