Welding Metallurgy of
01 Jan 1987-
About: The article was published on 1987-01-01 and is currently open access. It has received 991 citations till now. The article focuses on the topics: Welding.
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TL;DR: In this article, the authors present an overview of the key factors related to the formation of defects in welding methods commonly used with aluminium alloys, such as friction-stir welding, laser beam welding and arc welding.
Abstract: Transportation industries are obliged to address concerns arising from greater emphasis on energy saving and ecologically sustainable products. Engineers, therefore, have a responsibility to deliver innovative solutions that will support environmental preservation and yet meet industries’ requirements for greater productivity and minimised operational costs. Aluminium alloys have successfully contributed to meeting the rising demand for lightweight structures. Notable developments in aluminium welding techniques have resolved many welding related problems, although some issues remain to be addressed. The present study attempts to give an overview of the key factors related to the formation of defects in welding methods commonly used with aluminium alloys. First, a concise overview of defects found in friction-stir welding, laser beam welding and arc welding of aluminium alloys is presented. The review is used as a basis for analysis of the relationship between friction-stir welding process parameters and weld defects. Next, the formation and prevention of the main weld defects in laser beam welding, such as porosity and hot cracking, are discussed. Finally, metallurgical aspects influencing weld metal microstructure and contributing to defects are tabulated, as are defect prevention methods, for the most common flaws in arc welding of aluminium alloys.
129 citations
Cites background from "Welding Metallurgy of"
...Received: 12 March 2015 Accepted: 15 December 2015 Table 3 Common problems encountered in fusion welding of aluminium alloys, metallurgical aspects and prevention strategies (based on (Kou 2003))...
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Dissertation•
09 May 2012
TL;DR: In this paper, the influence of the processing conditions on microstructure and texture evolution and their resulting effect on the mechanical properties during additive manufacturing with a Ti6Al4V alloy, using three different techniques, namely, Selective laser melting (SLM), Electron beam selective melting (EBSM), and Wire arc additive manufacturing (WAAM) process.
Abstract: Additive Manufacturing (AM) is an innovative manufacturing process which offers near-net shape fabrication of complex components, directly from CAD models, without dies or substantial machining, resulting in a reduction in lead-time, waste, and cost. For example, the buy-to-fly ratio for a titanium component machined from forged billet is typically 10-20:1 compared to 5-7:1 when manufactured by AM. However, the production rates for most AM processes are relatively slow and AM is consequently largely of interest to the aerospace, automotive and biomedical industries. In addition, the solidification conditions in AM with the Ti alloy commonly lead to undesirable coarse columnar primary ? grain structures in components. The present research is focused on developing a fundamental understanding of the influence of the processing conditions on microstructure and texture evolution and their resulting effect on the mechanical properties during additive manufacturing with a Ti6Al4V alloy, using three different techniques, namely; 1) Selective laser melting (SLM) process, 2) Electron beam selective melting (EBSM) process and, 3) Wire arc additive manufacturing (WAAM) process. The most important finding in this work was that all the AM processes produced columnar ?-grain structures which grow by epitaxial re-growth up through each melted layer. By thermal modelling using TS4D (Thermal Simulation in 4 Dimensions), it has been shown that the melt pool size increased and the cooling rate decreased from SLM to EBSM and to the WAAM process. The prior ? grain size also increased with melt pool size from a finer size in the SLM to a moderate size in EBSM and to huge grains in WAAM that can be seen by eye. However, despite the large difference in power density between the processes, they all had similar G/R (thermal gradient/growth rate) ratios, which were predicted to lie in the columnar growth region in the solidification diagram. The EBSM process showed a pronounced local heterogeneity in the microstructure in local transition areas, when there was a change in geometry; for e.g. change in wall thickness, thin to thick capping section, cross-over?s, V-transitions, etc. By reconstruction of the high temperature ? microstructure, it has been shown that all the AM platforms showed primary columnar ? grains with a ? || Nz fibre texture with decreased texture strength from the WAAM to the EBSM and SLM processes. Due to a lack of variant selection, the room temperature ?-phase showed a weaker transformation ?-texture compared to the primary ?-texture with decreased texture strength in line with the reduction in ?-texture strength.The large ? grains observed in the WAAM process were not significantly affected by changes in the GTAW (Gas Tungsten Arc Welding) process parameters, such as travel speed, peak to base current ratio, pulse frequency, etc. However, an increased wire feed rate significantly improved the grain size. Another important finding from this work was that by combining deformation and AM the grain size was reduced to a greater extent than could be achieved by varying the arc or, heat source parameters. It has been shown that the large columnar ?-grain structure usually seen in the WAAM process, with a size of 20 mm in length and 2 mm in width, was refined down to ~ 150 �m by the application of a modest deformation, between each layer deposited. The EBSM process showed consistent average static tensile properties in all build directions and met the minimum specification required by ISO 5832-3 (for the wrought and annealed Ti6Al4V). The WAAM samples produced using more effective shielding and the standard pulsed GTAW system also showed average static properties that met the minimum specification required by AMS 4985C for investment casting and hipped Ti6Al4V alloy. Overall, the fatigue life of the samples that were produced by AM was very good and showed a better fatigue performance than the MMPDS design data for castings. However, there was a large scatter in the fatigue life due to the effect of pores.
129 citations
Cites background or methods from "Welding Metallurgy of"
...12: Effect of constitutional supercooling on solidification mode: (a) planar; (b) cellular; (c) columnar dendritic; and (d) equiaxed dendritic morphology ( S, L, and M denotes solid, liquid and mushy zone respectively) [46]....
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...S ]; Efficiency of GTAW process ~ 80 % [44, 46]...
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...The laser beam and electric arc efficiency was assumed to be 35 and 80 %, respectively [46, 48, 118]....
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...10: Nonplanar solidification structures in alloys; (a) transverse section of a cellularly solidified Pb–Sn alloy; (b) columnar dendrites in a Ni alloy; (c) equiaxed dendrites of a Mg–Zn alloy ; (d) three-dimensional view of dendrites in a Ni-base superalloy [44, 46]....
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...9: Basic solidification modes; (a) planar solidification of carbon tetrabromide; (b) cellular solidification of carbon tetrabromide with a small amount of impurity present; (c) columnar dendritic solidification of carbon tetrabromide with several percent impurity; (d) equiaxed dendritic solidification of cyclohexanol with impurity [46]....
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TL;DR: In this paper, the evolution of grain structure and topology in three dimensions in both the FZ and the HAZ considering the motion of the liquid pool was investigated. And the results showed that the grain size distributions and topological class distributions were largely unaffected by the temporal and spatial variations of the temperature created by different welding parameters.
126 citations
Cites background from "Welding Metallurgy of"
...This is because the FZ microstructure is influenced by the evolution of HAZ microstructure and both are affected by the transient three dimensional temperature field which depend on process variables [13,14]....
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...The propagating direction of a grain is determined by the local maximum heat flow direction [13]....
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...Both equiaxed and columnar grains form during welding and additivemanufacturing and curved columnar grains have been observed in the FZ of aluminum alloys [13]....
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...Grains with crystallographic directions closest to the heat flow direction compete more favorably over other grains and dominate the grain structure very close to the weld pool boundary [13]....
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...The subsequent growth is influenced by both the preferred crystallographic direction and the dominant local heat flow direction at the growth interface [13,14]....
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TL;DR: In this article, the authors summarize the recent progress in FSW of aluminium-magnesium alloys and recommend the upcoming guidance concerning to fabrication of aluminum-mag magnesium alloys through FSW.
Abstract: At present aluminium-magnesium alloys are widely used in various engineering applications due to its light weight and superior properties. Joining is considered as one of the most complex phenomenon in various precision industries like aerospace, railway, automotive and marine structures because inflexible tolerances are required during different product assembly. The friction stir welding (FSW) of aluminium-magnesium of various grade has incited substantial scientific and industrial importance since it has a potency to transform the product with a good quality joint. The fabrication of such alloys is a challenging task through conventional fusion welding due to its various metallurgical concerns. Therefore, the present work is intended to summarize the recent progress in FSW of aluminium-magnesium alloys. Particular attention has been paid to microstructural evolution, phase transformation, recrystallization mechanism, material flow behaviour and how the process parameters influence the various mechanical properties and associated defects during FSW. Various experimental and numerical simulation results have been mentioned for weld property comparison. Finally, this work not only points out the prominent conclusions of the preceding research but also recommends the upcoming guidance concerning to fabrication of aluminium-magnesium alloys through FSW.
120 citations
Additional excerpts
...welding process is a non-equilibrium process [95]....
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References
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TL;DR: In this article, the state of the art in selective laser sintering/melting (SLS/SLM) processing of aluminium powders is reviewed from different perspectives, including powder metallurgy (P/M), pulsed electric current (PECS), and laser welding of aluminium alloys.
1,172 citations
TL;DR: In this article, the authors show that the pre-existing dislocation network, which maintains its configuration during the entire plastic deformation, is an ideal modulator that is able to slow down but not entirely block the dislocation motion.
557 citations
TL;DR: In this article, the fundamental understanding of structure-properties relationship in automotive steels resistance spot welds is discussed. And a brief review of friction stir spot welding, as an alternative to RSW, is also included.
Abstract: Spot welding, particularly resistance spot welding (RSW), is a critical joining process in automotive industry. The development of advanced high strength steels for applications in automotive industry is accompanied with a challenge to better understand the physical and mechanical metallurgy of these materials during RSW. The present paper critically reviews the fundamental understanding of structure–properties relationship in automotive steels resistance spot welds. The focus is on the metallurgical characteristics, hardness–microstructure correlation, interfacial to pullout failure mode transition and mechanical performance of steel resistance spot welds under quasi-static, fatigue and impact loading conditions. A brief review of friction stir spot welding, as an alternative to RSW, is also included.
369 citations
TL;DR: In this article, a unified equation to compute the energy density is proposed to compare works performed with distinct equipment and experimental conditions, covering the major process parameters: power, travel speed, heat source dimension, hatch distance, deposited layer thickness and material grain size.
369 citations
TL;DR: This study attempted to predict solidification defects by DNN regression with a small dataset that contains 487 data points and found that a pre-trained and fine-tuned DNN shows better generalization performance over shallow neural network, support vector machine, and DNN trained by conventional methods.
314 citations