Investigation of microstructural homogeneity and thermal stability of equal channel angular pressed and aged 2024 Al alloy

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Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2014

Öğrenci: GÜHER KOTAN

Eş Danışman: YUNUS EREN KALAY, CEMİL HAKAN GÜR

Özet:

Attributed primarily to its uniqueness, simplicity and ability for effective strengthening through grain refinement without reduction in cross sectional area, equal channel angular pressing (ECAP) has been known as one of the most important metal working process. The implementation of ECAP with precipitation hardening exhibits a promising strengthening mechanism to be applied to age-hardenable metals. On the other hand, the combined effect of precipitation hardening and excessive plastic strain is quite complicated and needs detailed investigations to understand the basics of strengthening mechanisms. In this respect, the experimental work in this thesis represents a substantial step forward to understand the strengthening mechanism resulted by a combined implementation of ECAP and precipitation hardening in aluminum 2024. In the first part of this study, various aspects of ECAP and post ECAP precipitation in comparison to solutionized and aged counterpart were investigated. Homogenization contribution of precipitation process was monitored via micro-hardness indentation and the degree of homogenization was characterized by hardness inhomogeneity index (HII). The variation of hardness, hence strain levels, observed in two different samples was also investigated considering level of back pressure, magnesium content and sample conditions. In the second part, the response of ECAPed and post-ECAP aged samples, when subjected to long term and moderate temperatures up to 1000 hours was investigated. A limiting temperature was suggested for the safe use of an ECAPed Al 2024. Throughout the study microstructural characterizations were performed using high resolution electron microscopy (HREM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and optical microscopy.