Microstructural Aspects in FSW and TIG Welding of Cast ZE41A Magnesium Alloy
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MAGNESIUM alloys are of considerable interest to lightweight structure manufacturing, because of their low density, high specific strength, good thermal conductivity, excellent castability, and fine cutting performance.[1] On the other hand, the scarce corrosion resistance exhibited by most of the Mg alloys, as pointed out by Shi et al.,[2] poses some limits on their wide use. Some issues, related to the poor formability at room temperature and reduced creep resistance of Mg alloys, were remarked by Mordike and Ebert.[3] They argued that the further diffusion of Mg alloys relies on the development of new alloys, the improvement of the manufacturing processes, and the definition of opportune design criteria. In this regard, it has been claimed that the inclusion of well-selected alloying elements leads to a general enhancement of mechanical performance. Rare earth (RE) elements addition has many advantages, such as purifying alloy melt, modifying castability, refining the microstructure, improving the mechanical properties and anti-oxidation properties. Furthermore, Zirconium addition to RE elements has been shown to improve the mechanical properties due to grain refinement.[4,5] Some studies revealed that the dynamically recrystallized (DRX) grain size of wrought magnesium alloy was lower than that of as-cast
PIERPAOLO CARLONE and NICOLA PASQUINO, Assistant Professors, and FELICE RUBINO, Ph.D. Student, are with the Department of Industrial Engineering, University of Salerno, Fisciano, Italy. Contact e-mail:[email protected] ANTONELLO ASTARITA, Assistant Professor, is with the Department of Chemical Materials and Industrial Production Engineering, University of Naples Federico II, Naples, Italy. Manuscript submitted July 28, 2015. Article published online December 8, 2015. 1340—VOLUME 47B, APRIL 2016
magnesium alloy. In addition, the increasing rate of dynamic recrystallization in the as-cast material was considerably lower than the dynamic recrystallization in the wrought material.[6] Luka´cˇ and Trojanova´[7] discussed that the addition of rare earth (RE) elements into the material improves its ductility by weakening the basal texture. However, an enhancing of the corrosion rate is also exhibited, as evidenced by Zhao et al.[8] In this regard, recent studies proved the possibility to improve the corrosion resistance of Mg alloys containing RE elements, such as the ZE alloy, by means of heat treatments[9] and Vanadia-based[10] or epoxy-silane coatings.[11] Mg-Zn-RE alloys, such as the ZE41A alloy, manufactured by casting processes and T5 heat treated, are already successfully employed in the aeronautic and automotive industries. The development of adequate welding processes is considered as a key factor in spreading of Mg alloys for structural application. Tungsten Inert Gas (TIG) and Metal Inert Gas (MIG) processes are widely employed to join Mg alloys using high-purity shielding gases, but several issues still exist. TIG welding of Mg alloys exhibits relatively shallow penetration in single-pass welding and low
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