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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...[34] S. Kou, in Welding Metallurgy, (Ed: S. Kou 2002, 216– 242https://doi. org/10.1002/0471434027.ch9....
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01 Jan 2011
12 citations
Cites background from "Welding Metallurgy of"
...3d), may differ significantly from the fusion zone composition in aluminium alloys [131], [137]....
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TL;DR: In this article , the microstructural evolution of NAB alloys in the cast, wrought, friction stir processed, arc-welded, electron beam welded and laser welding conditions is discussed.
Abstract: Nickel-aluminum bronze (NAB) alloys are commonly used for marine applications such as propellers by the U.S. Navy. These NAB components are conventionally manufactured using casting techniques, but recent interest has shifted to the possibility of additive manufacturing (AM) processes. The following literature review discusses the microstructural evolution of (nominally) Cu-9Al-5Ni-5Fe-1Mn NAB alloys in the cast, wrought, friction stir processed, arc-welded, electron beam welded and laser-welded conditions. NAB alloys exhibit a complex microstructure, consisting of a mixture of five κ precipitates distributed in an α or β’ martensitic matrix. The size, morphology, and distribution of these phases are sensitive to changes in cooling rate and thermal history such as those imposed by AM and welding. Although the microstructure is well documented under casting conditions, no continuous cooling diagrams have been developed to describe phase transformations under arc and laser processing conditions for NAB. As such, this review investigates recent reports related to arc, electron beam and laser-based additive manufacturing processes and the associated microstructures and properties. Studies have reported additively manufactured NAB alloys with improved properties compared to cast material, associated with differences in microstructure. At moderate cooling rates, such as those associated with arc-based processing, the microstructure consists of Widmanstätten α and various κ phases, which become more refined with increasing cooling rate. This leads to an improvement in the tensile properties of wire-arc direct energy deposited NAB, with > 17% increase in yield strength and > 90% increase in ductility when compared to cast material. At rapid cooling rates representative of laser-based and electron beam processing, the microstructure consists primarily of a twin-related β’ martensite with nanoscale κ phases. This leads to a significant increase in yield strength (>60–100%) at the expense of ductility (<−30%) when compared to cast material. Additionally, previous studies have reported that the refined microstructure from these high cooling rate processes leads to an improvement in the corrosion resistance of as deposited NAB. There is also evidence that the conventional heat treatments for cast NAB alloys need to be optimized for additively manufactured materials. The report includes the methods and challenges associated with characterizing NAB alloys under these processing conditions and provides recommendations for future research.
12 citations
TL;DR: In this article, the effects of activating fluxes on macromorphologies, microstructures and mechanical properties of low power pulse laser beam welding of AZ31 magnesium alloy joints were investigated by microstructural observations.
Abstract: Effects of activating fluxes on macromorphologies, microstructures and mechanical properties of low power pulse laser beam welding of AZ31 magnesium alloy joints were investigated by microstructural observations and mechanical properties tests (including the ultimate tensile strength and hardness). The results showed that activating flux (SiO2) is more effective in improving the laser welded penetrations when the heat input is at a critical value (E = 53·42 J mm−1). Five typical fluxes (SiO2, TiO2, ZnCl2, CaCl2 and CaF2) all increased the weld penetrations and D/W ratios of the welded joints. The morphologies of grains in the band zones with fluxes are characterised by dendritic crystals. Moreover, the widths of the band zones with oxide and chloride fluxes are wider than that with fluorine flux. The mechanical properties of the welded joints with fluxes were lower than those without flux. The fracture surface of the welded joints with fluxes exhibited a character of a mixed fracture.
12 citations
01 Sep 2022-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper , various DED process conditions were employed to fabricate crack-free Al 7075 samples, and double aging combined with solution treatment was performed on the as-built materials thanks to the precipitation hardening nature of the material.
Abstract: Laser directed energy deposition (DED) is an attractive additive manufacturing (AM) technique to fabricate high-strength Al 7075 alloy components for various applications. However, its poor weldability and easy occurrence of cracks during the highly non-equilibrium process have limited the adoption of this material for AM. In this research, various DED process conditions were employed to fabricate crack-free Al 7075 samples, and double aging combined with solution treatment was performed on the as-built materials thanks to the precipitation hardening nature of Al 7075. The influences of DED process parameters and heat treatment on microstructure and mechanical properties were investigated. It was found that the setting of laser power at 280 W and scanning speed at 500 mm/min led to crack-free material deposition with the highest density among all conditions investigated. Compared with the as-built Al 7075, the average micro-hardness of the alloy increased from 91.73 to 144.91 HV, and the ultimate tensile strength increased from 233.18 to 342.16 MP after heat treatment. Meanwhile, it was discovered that mass Cu elements are segregated at grain boundaries (GBs) for the as-built material. The existence of Al2Cu phase at GBs is believed to effectively mitigate the hot cracking, and the coherent strengthening mechanism of Cu segregation to the Al GBs is discussed. In addition, it was shown that Mg and Zn contents increased at the GBs after heat treatment, which tend to form precipitated phases and lead to the improved mechanical properties for DED produced Al 7075.
12 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 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.
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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
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.
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