Texture Development in a Friction Stir Lap-Welded AZ31B Magnesium Alloy
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INTRODUCTION
THE considerable challenges facing the transportation industry are rooted to the increasing concerns about global climate change in conjunction with highly volatile and rising energy prices.[1–6] With the understanding that roughly 85 pct of the anthropogenic environment-damaging emissions generated by aircraft and ground vehicles occur from their useful life, it is unsurprising that lightweight design has become a key strategy by which the transportation sector can address the greater world-wide societal demands for environmental and ecological stewardship and consumer demands for improved fuel efficiency and economy.[7–10] With due consideration of different lightweight materials (e.g., aluminum alloys, advanced high strength steels, magneB.S. NAIK, Ph.D. Student, and D.L. CHEN, Professor and Ryerson Research Chair, are with the Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada. Contact e-mail: [email protected] X.CAO, Adjunct Professor, is with the Department of Mechanical and Industrial Engineering, Ryerson University, and also Senior Research Officer with the National Research Council Canada - Aerospace, 5145 Decelles Avenue, Montreal, QC H3T 2B2, Canada. P. WANJARA, Group Leader, is with the National Research Council Canada - Aerospace. This note applies only to authors Cao and Wanjara: Published with permission of the National Research Council of Canada in right of the Crown of Canada. Manuscript submitted August 2, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
sium alloys, titanium alloys, and composites) for nextgeneration transportation aircraft and vehicles in the aerospace, automotive and rail industries, magnesium alloys offer a good combination of properties including low density, high strength-to-weight ratio, environmental friendliness, castability, and recyclability.[1,11–17] However, due to the limited number of slip systems in the hexagonal close-packed (hcp) crystal structure, magnesium alloys may be restricted in their widespread use by their poor ductility at room temperature. To diversify and expand the use of magnesium alloys in the transportation sector, enabling joining technologies are enviable for realizing cost-effective manufacturing and high performance assemblies. Several joining technologies have shown potential for assembly of magnesium alloys including conventional arc and advanced fusion (e.g., laser and electron beam) welding as well as friction stir welding (FSW). As the solidification defects and structure (e.g., dendritic, coarse grains) in the fusion zone of welded magnesium alloys limit the mechanical performance, the realization of a solid-state joint using FSW is especially propitious for mitigating the formation of gas porosity, reducing the susceptibility to solidification cracking, limiting the compositional segregation of alloying elements and promoting/maintaining a wrought microstructure in the weldment. Moreover, the low heat input and process flexibility of FSW enable assembly of different
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