Investigation of Fe-rich fragments in aluminum-steel friction stir welds via simultaneous Transmission Kikuchi Diffraction and EDS

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• 作者：Majid Abbasi^a ; ¹ ; ^{majid.abbasi@kist.re.kr" class="auth_mail" title="E-mail the corresponding author} ; ^{majid.abbasi.g@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Morteza Dehghani^b ; ^c ; ¹ ; ^{mdehghany@ut.ac.ir" class="auth_mail" title="E-mail the corresponding author} ; Hwan-Uk Guim^d ; Dong-Ik Kim^a ; ^{dongikkim@kist.re.kr" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Friction stir welding (FSW) ; Transmission Kikuchi diffraction (TKD) ; Transmission electron backscattered diffraction (t-EBSD) ; Al-Fe intermetallics ; Nano-twinning ; Texture
• 刊名：Acta Materialia
• 出版年：2016
• 出版时间：15 September 2016
• 年：2016
• 卷：117
• 期：Complete
• 页码：262-269
• 全文大小：4270 K

文摘

An attempt has been made to investigate Fe-rich fragments and surrounding intermetallic compounds in aluminum-steel friction stir welds using conventional EBSD + EDS as well as advanced Transmission Kikuchi Diffraction (TKD). Results indicate that the fragments are covered by a layer of orthorhombic Al₅Fe₂. This layer is surrounded by a mixed region composed of sub-micrometer Al₃Fe crystals in a matrix of Al nano grains. Employing high beam current TKD on electron-transparent samples enables investigation of sub-micrometer grains in the mixed region with a higher spatial resolution than conventional EBSD. As a result, nano-twinning in Al in the mixed region has been observed. Microstructural and texture results imply that Fe-rich fragments travel through the Al matrix under extreme shear forces, severely refining Al grains, and inducing nano-twinning. Due to extreme shear forces and Fe outward diffusion, fine steel fragments dissolve in the surroundings leading to the nucleation of nano Al₃Fe crystals particularly along Al grain boundaries. Al₃Fe crystals consume the Al matrix as they grow in size and fraction.