Macro and Microstructural Effects of the Application of an Induced Axial Magnetic Field During the Deposition of Aluminu
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Macro and Microstructural Effects of the Application of an Induced Axial Magnetic Field During the Deposition of Aluminum Weld Beads M. A. García, V. H. López M., R. García H., F. F. Curiel L., R. R. Ambríz R. Instituto de Investigaciones Metalúrgicas. Universidad Michoacana de San Nicolás de Hidalgo. Apdo. postal 888, Centro, C.P. 58000. Morelia, Mich., México. E-mail: [email protected].
ABSTRACT In this work, aluminum weld beads were deposited on aluminum plates of commercial purity (12.7 mm thick), using an ER-5356 filler wire. The aim of the experiments was to assess the effects that yield the induction of an axial magnetic field (AMF) during the application of the weld beads using the direct current gas metal arc welding process (DC-GMAW). An external power source was use to induce magnetic fields between 0 to 28 mT. The effects of the magnetic fields were assessed in terms of the macrostructural features of the deposits, morphology of the grain structure, grain size and grain size distribution in the weld metal. Macrostructural characteristics of the weld beads revealed that increasing the intensity of the magnetic induction to produce a magnetic field above 14 mT, leads to a significant loss of feeding material and there is a tendency of the deposits to increase their width and reduce penetration. Perturbation of the weld pool induced by the application of the AMF noticeably modified the grain structure in the weld metal. In particular, for the intensities of 5 and 14 mT, columnar growth was essentially non-existent. Grain size distribution plots showed, generally speaking, that the use of magnetic fields is an efficient method to produce homogeneous grain structures within the weld metal. Finite element analysis was used to explain the weld bead geometry with the intensity of the magnetic field. INTRODUCTION Typically, fusion welding processes exhibit a columnar grain structure in the region adjacent to the fusion line. Aluminum and its alloys are not an exception to this type of solidification. This feature represents a microstructural discontinuity which affects the mechanical properties of the welded joint. A number of attempts have been made to suppress this type of structure. Literature review shows that the induction of magnetic fields during welding can be effective in homogenizing the grain structure in the weld metal, in steel, aluminum and titanium alloys [110]. In particular, for aluminum alloys some success has been found with the gas tungsten arc welding process [1, 3, 6, 9]. Also, it has been reported that the use of magnetic fields prevents hot cracking that occurs in some aluminum alloys [1, 9]. According to Kou [2], in a weld, several mechanisms are involved in the formation of new substrates for the nucleation of grains in the weld pool; a) heterogeneous nucleation due to the presence of inoculants or a possible increase of the constituents in the undercooling, b) separation of the grains as a result of convective flow, c) fragmentation of the dendrites or their arms and d) surface nuclea
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