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Microstructure and Quasi-Static Mechanical Behavior of Cryoforged AA2519 Alloy

Materials Sciences and Applications 2019年第2期10卷 137-149页

作者： Amin Azimi gbadebo moses owolabi Hamid Fallahdoost Nikhil Kumar Horace Whitworth Department of Mechanical Engineering Howard University Washington DC USA Department of Mechanical Engineering Materials Science and Engineering Program Binghamton University (SUNY) Binghamton NY USA

In this study, AA2519 alloy was initially processed by multi axial forging (MAF) at room and cryogenic temperatures. Subsequently, the microstructure and the mechanical behavior of the processed samples under quasi-static loading were investigated to determine the influence of cryogenic forging on alloys’ subgrains dimensions, grain boundaries interactions, strength, ductility and toughness. In addition, the failure mechanisms at the tensile rupture surfaces were characterized using scanning electron micro-scope (SEM). The results show significant improvements in the strength, ductility and toughness of the alloy as a result of the cryogenic MAF process. The formation of nanoscale crystallite microstructure, heavily deformed grains with high density of grain boundaries and second phase breakage to finer particles were characterized as the main reasons for the increase in the mechanical properties of the cryogenic forged samples. The cryogenic processing of the alloy resulted in the formation of an ultrafine grained material with tensile strength and toughness that are ~41% and ~80% higher respectively after 2 cycles MAF when compared with the materials processed at ambient temperature. The fractography analysis on the tested materials shows a substantial ductility improvement in the cryoforged (CF) samples when compared to the room temperature forged (RTF) samples which is in alignment with their stress-strain profiles. However, extended forging at higher cycles than 2 cycles led only to increase in strength at the expense of ductility for both the CF and RTF samples.

关键词： AA2519 Aluminum Alloy Cryogenic Forging Quasi-Static Mechanical Behavior Microstructure Investigation Fractography Analysis

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Fatigue Responses of Three AA 2000 Series Aluminum Alloys

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Journal of Materials Science and Chemical Engineering 2019年第3期7卷 32-48页

作者： gbadebo moses owolabi Mark Thom Olusegun Ajide Nikhil Kumar Amin Azimi Horace Whitworth Grant Warner Department of Mechanical Engineering Howard University Washington DC USA Department of Mechanical Engineering University of Ibadan Ibadan Nigeria

In this paper, smooth specimens of three aluminum alloys: AA 2219-T8, AA 2519-T8 and AA 2624-T351, were subjected to the same level of uniaxial (tension/compression) fatigue loading to compare their fatigue responses. Fractographic investigations of the failed specimens after fatigue loading was also conducted using a scanning electron microscope. The fatigue test results showed considerable differences in the fatigue lives of the three investigated alloys with AA 2219-T8 having the shortest fatigue life and AA 2624-T351 the longest fatigue life. The fractographic analysis showed that coalescence of micropores, microvoids, particles cleavage and microcracks are the predominant features in the fracture surface of AA 2219-T8. The fracture surface features of AA 2519-T8 revealed higher resistance to fatigue cracks nucleation and growth when compared to AA 2219-T8. The features depicted mainly partly ductile and partly brittle fracture. The AA 2624-T351 fracture surface features revealed noteworthy ductile failure mechanism. The results suggest a strong correlation between the surface fractographic features and the fatigue lives of the alloys. It is also observed that in addition to the yield strengths and ultimate tensile strengths, the total strain energy densities (SED) may provide a reasonable indication of the relative fatigue performance of the three alloys. AA 2219-T8 had the lowest SED and the lowest fatigue life, while AA 2624-T351 had the highest SED and the highest fatigue life. Thus, AA 2624-T351 would be the most suitable materials for components subjected to fatigue loading.

关键词： Fatigue Life Aluminum Alloy Strain Energy Density Fractography

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