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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06 Aug 2012TL;DR: In this paper, beam modulation has been used in conventional fusion welding to promote grain refinement for additive manufacturing processes including electron beam freeform fabrication (EBF(sup 3)) and gas-tungsten arc (GTA) deposition to alter solidification behavior and produce a refined microstructure.
Abstract: Grain refinement can significantly improve the mechanical properties of freeform-fabricated Ti-6Al-4V alloy, promoting increased strength and enhanced isotropy compared with coarser grained material. Large beta-grains can lead to a segregated microstructure, in regard to both alpha-phase morphology and alpha-lath orientation. Beam modulation, which has been used in conventional fusion welding to promote grain refinement, is explored in this study for use in additive manufacturing processes including electron beam freeform fabrication (EBF(sup 3)) and gas-tungsten arc (GTA) deposition to alter solidification behavior and produce a refined microstructure. The dynamic molten pool size induced by beam modulation causes rapid heat flow variance and results in a more competitive grain growth environment, reducing grain size. Consequently, improved isotropy and strength can be achieved with relatively small adjustments to deposition parameters.
13 citations
Cites background from "Welding Metallurgy of"
...Beam and arc modulation are common methods of microstructural refinement in traditional fusion welding of Ti-6Al-4V for many reasons, including decreased hot cracking and increased fracture toughness [17-20]....
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TL;DR: In this paper, the susceptibility of austenitic, ferritic, and duplex stainless steels to solidification cracking was evaluated by the Transverse Motion Weldability (TMW) test.
Abstract: The susceptibility of austenitic, ferritic, and duplex stain-less steels to solidification cracking was evaluated by the new Transverse Motion Weldability (TMW) test. The focus was on austenitic stainless steels. 304L and 316L were least susceptible, 321 was significantly more susceptible, and 310 was much more susceptible. However, some 321 welds were even less susceptible than 304L welds. These 321 welds were found to have much finer grains to better resist solidification cracking. Quenching 321 during welding revealed spontaneous grain refining could occur by heterogeneous nucleation. For 304L, 316L, and 310, a new explanation for the susceptibility was proposed based on the continuity of the liquid between columnar dendrites; a discontinuous, isolated liquid allows bonding between dendrites to occur early to better resist cracking. In 304L and 316L, the dendrite-boundary liquid was discontinuous and isolated, as revealed by quenching. The liquid was likely depleted by both fast back diffusion into -dendrites (body-centered cubic) and the L + + reaction, which consumed L while forming . In 310, however, the dendrites were separated by a continuous liquid that prevented early bonding between them. Back diffusion into -dendrites (face-centered cubic) was much slower, and the L + + reaction formed little . Quenching also revealed skeletal/lacy formed in 304L and 316L well after solidification ended; thus, skeletal/lacy did not resist solidification cracking, as had been widely believed for decades. The TMW test further demonstrated that both more sulfur and slower welding can increase susceptibility.
13 citations
TL;DR: In this article, the weldability of resistance spot welding affected by different thermal, physical, and metallurgical properties is extensively investigated by realistically computing transient mass, momentum, energy, species, and magnetic field intensity transport in the alloy workpieces and electrodes.
Abstract: The weldability of resistance spot welding affected by different thermal, physical, and metallurgical properties is extensively investigated by realistically computing transient mass, momentum, energy, species, and magnetic field intensity transport in the alloy workpieces and electrodes. The properties considered are the thickness, radius, equilibrium partition coefficient of workpieces, electrode-to-workpiece electrical conductivity ratio, thermal conductivity ratio, and a joule heat-to-enthalpy change parameter. Resistance spot welding has been widely used in joining thin workpieces in various electronic packaging and manufacturing industries. Understanding of physical mechanisms for easily manipulating and controlling weld qualities in advance is important. This paper accounts for electromagnetic force, heat generations due to contact resistances at the electrode-workpiece interface and faying surface between workpieces, and temperature-dependent bulk resistance of the workpiece. The contact resistances are functions of hardness, temperature, electrode force, and surface condition. The computed results in general dimensionless expressions show that the welding is feasible or onset time is shortened by decreasing thickness, radius, equilibrium partition coefficient of the workpiece, and electrode-to-workpiece electrical conductivity and thermal conductivity ratios, and increasing the joule heat-to-enthalpy change parameter. The corresponding heat transfer and species patterns are also presented.
13 citations
Cites background from "Welding Metallurgy of"
...2175226 Heating a metal during welding affects its structure, determined by the welding time, fusion zone shape, temperature, cooling rate, and the composition of the metal [9], [10]....
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TL;DR: In this article, a microstructural characterisation of welds performed by resistance seam welding was carried out, with special focus on weld defect analysis, in order to perform a comparative weldability analysis, the welds were performed using similar welding procedures.
Abstract: In the present investigation, a microstructural characterisation of welds performed by resistance seam welding was carried out, with special focus on weld defect analysis. In order to perform a comparative weldability analysis, the welds were performed using similar welding procedures. Similar welds in aluminium (5754-H22) and zinc (Zintek) alloys, as well as dissimilar welds between galvanised steel and zinc, were studied. The defective aluminium welds were found to be characterised by important grain growth inside an inhomogeneous nugget and by the presence of important voids and cracks. The zinc welds showed a well defined nugget, but with porosities and some cracks. In the dissimilar steel–zinc welds, important macroscopic defects were observed. Microstructural analysis evidenced the occurrence of melting at the zinc side of the welds; meanwhile, no microstructural modifications could be observed for the steel side. Defect formation, as well as weld morphologies, was related to the variation i...
13 citations
Cites background from "Welding Metallurgy of"
...Formation of equiaxed grains takes place in this zone of the weld where the thermal gradients become insignificant.(7,28) Depending on the application to which this material will be subjected, a greater overlap between successive weld nuggets may be required, in order to confer a better mechanical resistance to the weld....
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01 Jan 1998
Abstract: AbstractCracking, or disbonding, along the fusion boundary in dissimilar metal welds has been a persistent problem, particularly in applications where austenitic alloys are clad on to structural steels for corrosion protection. Many failures in dissimilar metal welds occur as a result of cracking along a boundary that runs parallel to the fusion boundary in the adjacent weld metal. A preliminary investigation was undertaken to determine the nature and evolution of boundaries and structure in dissimilar metal welds using a simple ternary system composed of a pure iron substrate and a 70Ni–30Cu (Monel) filler metal. Changes in base metal dilution were found to alter the evolution of boundaries and structures near the fusion boundary dramatically. Optical metallography and electron microanalysis reveal that the resulting weld microstructures and boundaries are similar to those observed in engineering materials used for cladding and corrosion resistant overlay. Transmission electron diffraction analysis revea...
13 citations
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.
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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
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