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조민구,김한진,강민정,Phaniraj P. Madakashira,박은수,서진유,김동익,홍성태,한흥남 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.1
The high entropy alloy CrMnFeCoNi has been shown to have promising structural properties. For a new alloy to beused in a structural application it should be weldable. In the present study, friction stir welding (FSW) and laserwelding (LW) techniques were used to butt weld thin plates of CrMnFeCoNi. The microstructure, chemical homogeneityand mechanical behavior of the welds were characterized and compared with the base metal. The tensilestress-strain behavior of the welded specimens were reasonable when compared with that of the base metal. FSWrefined the grain size in the weld region by a factor of ~14 when compared with the base metal. High-angle annulardark field transmission electron microscopy in combination with energy dispersive X-ray spectroscopy showedchemical inhomogeneity between dendritic and interdendritic regions in the fusion zone of LW. Large fluctuationsin composition (up to 15 at%) did not change the crystal structure in the fusion zone. Hardness measurementswere carried out in the weld cross section and discussed in view of the grain size, low angle grain boundaries andtwin boundaries in FSW specimens and the dendritic microstructure in LW specimens.
Jeong, Hye-Jin,Kim, Moon-Jo,Park, Ju-Won,Yim, Chang Dong,Kim, Jae Joong,Kwon, Oh Duck,Madakashira, Phaniraj P.,Han, Heung Nam Elsevier 2017 Materials science & engineering. properties, micro Vol.684 No.-
<P><B>Abstract</B></P> <P>In this study, the tensile deformation behavior of as-extruded AZ91 magnesium alloy under pulsed electric current has been investigated based on microstructural observations. The flow stress decreased and the elongation increased remarkably on applying electric current in comparison with non-pulsed tensile test at both room temperature and at 70°C. The results of EBSD and EDS analysis showed that dissolution of the Mg<SUB>17</SUB>Al<SUB>12</SUB> phase obviously occurs during pulsed tensile test due to thermal effect caused by Joule heating and athermal effect of electric current. To distinguish the athermal and thermal effects of electric current, the induction heat treatment (IHT) that follows the temperature cycle measured during pulsed tensile test was carried out using a dilatometer, which could control the temperature of specimen by an induction heater in a vacuum. Additionally, electropulsing treatment (EPT) was conducted and compared with the conventional heat treatment (CHT) under the same condition. The fraction of Mg<SUB>17</SUB>Al<SUB>12</SUB> phase after pulsed tensile test and EPT was obviously lower in comparison with IHT and CHT, respectively. The results prove that applying electric current accelerates dissolution of Mg<SUB>17</SUB>Al<SUB>12</SUB> phase in as-extruded AZ91 alloy with a distinct effect from Joule heating during deformation. It is proposed that electrically-assisted manufacturing (EAM) technique can improve the efficiency of forming process for as-extruded AZ91 alloy.</P>