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Nunez E.E.N.,University of Caribe | Silgado J.U.,University of Caribe | Salcedo J.E.T.,Universidad del Norte, Colombia | Ramirez A.J.,Metals Characterization and Processing Laboratory
Soldagem e Inspecao | Year: 2014

Problems of industries and manufacturers of welded structures in aluminum alloys are centered on reduction of mechanical properties in welded joints due to heat input effects on heat affected zone (HAZ); as well as, effects of discontinuities and metallurgical defects, high cost repairs, and low productivity. The aim of this work is to evaluate the influence of gas mixtures 80Ar20He (MG1), 60Ar40He (MG2), 80Ar19He1O2 (MG3), and 60Ar39He1O2 (MG4), on aluminum alloy AA5083-O weldability using filler metal ER5183 automated GMAW-P process. Methodology has included a factorial experiment design, customization of welding parameters, characterization of base metal and welding regions. Analysis of results were carried out based on microstructure evaluation of welding regions, measurements of hardness and tensile properties, observations of discontinuities and defects, costs evaluation, and welding speed. Results show that gas mixtures with O2 are highly beneficial to obtain good weldability of studied alloy. © 2014, Universidade Federal de Uberlandia. All rights reserved.


Unfried-Silgado J.,Metals Characterization and Processing Laboratory | Unfried-Silgado J.,University of Campinas | Unfried-Silgado J.,Autonomous University of the Caribbean | Ramirez A.J.,Metals Characterization and Processing Laboratory
Metals and Materials International | Year: 2014

In part II of this work is evaluated the as-welded microstructure of Ni-Cr-Fe alloys, which were selected and modeled in part I. Detailed characterization of primary and secondary precipitates, subgrain and grain structures, partitioning, and grain boundary morphology were developed. Microstructural characterization was carried out using optical microscopy, SEM, TEM, EBSD, and XEDS techniques. These results were analyzed and compared to modeling results displaying a good agreement. The Hf additions produced the highest waviness of grain boundaries, which were related to distribution of Hf-rich carbonitrides. Experimental evidences about Mo distribution into crystal lattice have provided information about its possible role in ductility-dip cracking (DDC). Characterization results of studied alloys were analyzed and linked to their DDC resistance data aiming to establish relationships between as-welded microstructure and hot deformation performance. Wavy grain boundaries, primary carbides distribution, and strengthened crystal lattice are metallurgical characteristics related to high DDC resistance. © 2014 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.


Unfried-Silgado J.,Metals Characterization and Processing Laboratory | Unfried-Silgado J.,University of Campinas | Unfried-Silgado J.,Autonomous University of the Caribbean | Wu L.,Metals Characterization and Processing Laboratory | And 3 more authors.
Materials Science and Engineering A | Year: 2012

The stacking fault energy (SFE) in a set of experimental Ni-Cr-Fe alloys was determined using line profile analysis on synchrotron X-ray diffraction measurements. The methodology used here is supported by the Warren-Averbach calculations and the relationships among the stacking fault probability (α) and the mean-square microstrain (<ε 2 L>). These parameters were obtained experimentally from cold-worked and annealed specimens extracted from the set of studied Ni-alloys. The obtained results show that the SFE in these alloys is strongly influenced by the kind and quantity of addition elements. Different effects due to the action of carbide-forming elements and the solid solution hardening elements on the SFE are discussed here. The simultaneous addition of Nb, Hf, and, Mo, in the studied Ni-Cr-Fe alloys have generated the stronger decreasing of the SFE. The relationships between SFE and the contributions on electronic structure from each element of additions were established. © 2012 Elsevier B.V.


Unfried-Silgado J.,Metals Characterization and Processing Laboratory | Unfried-Silgado J.,University of Campinas | Unfried-Silgado J.,Autonomous University of the Caribbean | Ramirez A.J.,Metals Characterization and Processing Laboratory
Metals and Materials International | Year: 2014

This work aims the numerical modeling and characterization of as-welded microstructure of Ni-Cr-Fe alloys with additions of Nb, Mo and Hf as a key to understand their proven resistance to ductility-dip cracking. Part I deals with as-welded structure modeling, using experimental alloying ranges and Calphad methodology. Model calculates kinetic phase transformations and partitioning of elements during weld solidification using a cooling rate of 100 K.s -1, considering their consequences on solidification mode for each alloy. Calculated structures were compared with experimental observations on as-welded structures, exhibiting good agreement. Numerical calculations estimate an increase by three times of mass fraction of primary carbides precipitation, a substantial reduction of mass fraction of M23C6 precipitates and topologically closed packed phases (TCP), a homogeneously intradendritic distribution, and a slight increase of interdendritic Molybdenum distribution in these alloys. Incidences of metallurgical characteristics of modeled as-welded structures on desirable characteristics of Ni-based alloys resistant to DDC are discussed here. © 2014 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.

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