Physically Based Model of the Yield Strength for an Al-Mg-Si-Cu-Zn Alloy
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OVER the past five decades, tremendous amount of work has been done on developing a framework for modeling the strength as well as work hardening of face-centered cubic and body-centered cubic metals.[1–8] In 1990, Shercliff and Ashby introduced the idea of process modeling to systematically estimate the yield strength of age-hardenable Al alloys based on established principles of phase equilibria, precipitate coarsening, and dislocation–precipitate interactions.[6,7] It is generally accepted that the yield strength of precipitation-hardenable Al alloys receives contributions from intrinsic strength of aluminum as well as solid solution and precipitation strengthening effects.[6,7,9–13] Studies on the strengthening mechanisms for precipitation-hardenable alloys have been focused on understanding their yield stress in terms of dislocation–precipitate interactions since the nature of these interactions has a dominant effect on their mechanical behavior.[9,10,12,14,15] Although multiple mechanisms are known which describe the POOYA HOSSEINI-BENHANGI, formerly M.Sc. from the Department of Materials Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, P.O. Box 91775-1111, Mashhad, Iran, is now a Ph.D. Candidate with the Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC V6T 1Z3, Canada. MOHAMMAD MAZINANI, Associate Professor, and MOHSEN HADDADSABZEVAR, Professor, are with the Department of Materials Engineering, Faculty of Engineering, Ferdowsi University of Mashhad. Contact e-mail: [email protected] Manuscript submitted January 5, 2015. Article published online September 4, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS A
physical nature of these interactions, their effects often overlap in case of the alloys of commercial interest. This makes the development of detailed models very challenging. As such, recent yield stress models have assumed a generic linear relationship between the precipitate strength and size of the precipitates that are assumed to be shearable.[11,16–18] In practice, a more useful question to consider is whether the mobile dislocations pass through the precipitates (shearable) or bypass them on the basis of the Orowan mechanism (non-shearable).[19] The precipitates’ size has been used for the characterization of their shearable/non-shearable transition, and accordingly, it has been assumed as the critical adjustable parameter in developing physically based models for yield strength of precipitation-hardening alloys.[20] 6000 series aluminum alloys are considered the alloys of choice in the automotive industry for lightweight skin panel applications.[12] The widespread applications of these alloys, however, require further research and development in various areas related to process optimization and properties of this series of alloys.[21] The degree of strengthening is highly dependent on the aging process, which controls the nature of the precipitates, their volume fraction, average size, and spatial distribution,
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