Influences of Hydrogen Micropores and Intermetallic Particles on Fracture Behaviors of Al-Zn-Mg-Cu Aluminum Alloys
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INTRODUCTION
AL-ZN-MG-CU aluminum alloys are widely used in the fields of aerospace because of their high strength and strength-to-weight ratio.[1–3] Fracture toughness is also being treated as a crucial parameter for such an application.[4] Fracture mechanisms of ductile metals are often attributed to microscopic void evolution that is consisted of void initiation, growth, and coalescence.[5–9] It is reasonable to assume that the growth and coalescence of voids, which are nucleated on intermetallic particles, are influenced by the strength, distribution, and morphology of particles.[10,11] For Al-Zn-Mg-Cu aluminum alloys, a variety of intermetallic particles, such as Al7Cu2Fe (incoherent inclusions), Mg2Si (incoherent inclusions), MgZn2 (incoherent precipitates), Al32(Mg,Zn)49 (coherent T phase particles), and Al2CuMg (incoherent S phase particles), have been identified.[12,13] However, the particles’ fracture and related void evolution during the fracture process of Al-Zn-Mg-Cu aluminum alloys have not been fully understood yet.
HANG SU, Ph.D. Candidate, TAKURO YOSHIMURA, Graduate Student, HIROYUKI TODA, Professor, and MD. SHAHNEWAZ BHUIYAN, Research Assistant Professor, are with the Department of Mechanical Engineering, Kyushu University, 744, Motooka, Nishiward, Fukuoka 819-0395, Japan. Contact e-mail: [email protected] KENTARO UESUGI and AKIHISA TAKEUCHI, Researchers, are with Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1, Kouto, Mikazuki-cho, Sayogun, Hyogo 679-5198, Japan. NOBUHITO SAKAGUCHI and YOSHIO WATANABE, Researchers, are with UACJ Coporation, Chitose 3-1-12, Minato-ward, Nagoya, Aichi 455-8670, Japan. Manuscript submitted April 18, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
In recent studies, it has been revealed that pre-existing hydrogen micropores in aluminum alloys play a significant role in a ductile fracture process.[14,15] Several studies have reported that hydrogen micropores which are initiated heterogeneously on intermetallic particles during the homogenization process grow during a high-temperature heat treatment and remain even after extensive plastic deformation during hot and cold rolling.[16,17] In addition, hydrogen micropores that are nucleated on particles influence triaxial stress field and associated particles damage.[15,18,19] It has been well documented that hydrogen micropores exhibit premature growth together with void growth due to the fracture of Al2CuMg particles during loading in wrought Al-Cu-Mg aluminum alloys.[20–22] For Al-Zn-Mg-Cu aluminum alloys, which contain a variety of intermetallic particles, little is known about the influence of pre-existing hydrogen micropores on intermetallic particles fracture and related voids evolution during a fracture process. Except pre-existing hydrogen micropores, hydrogen atoms trapped in other defects also influence the fracture of Al-Zn-Mg-Cu aluminum alloys. Sofronis et al. have suggested that hydrogen atoms enhance the mobility of dislocations that result in the reduction of plastic instabilities during uniax
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