Tensile fracture behavior of AA7075 alloy produced by thixocasting
(Department of Metallurgical and Materials Engineering, Faculty of Technology,
Gazi University, 06500 Teknikokullar, Ankara, Turkey)
Gazi University, 06500 Teknikokullar, Ankara, Turkey)
Abstract: Tensile fracture behaviors of thixocast, artificially aged thixocast (thixocast+T6) and as-extruded AA7075 alloys were investigated. The microstructural and fractographic observations were carried out using optical microscope (OM) and scanning electron microscope (SEM). Experimental studies showed that as-extruded and thixocast+T6 specimens exhibited considerably more excellent mechanical properties than as-thixocast AA7075 specimen. T6 artificial heat treatment with prolonged solution treatment significantly improved the tensile properties of the thixocast AA7075 alloy. The tensile properties of as-extruded and thixocast+T6 specimens were close to each other. In as-thixocast specimen having remarkable micro-cracks, fracture was intergranular brittle type. The ductile fracture surfaces were observed in as-extruded and thixocast+T6 specimens. In as-thixocast specimens, decohesion started between the eutectic-matrix interfaces and propagated through grains. Micro-void coalescence was the dominant form of fracture in thixocast+T6 heat treated specimens. The micro-voids nucleation was initiated at the interface between the matrix and multinary eutectic structure.
Key words: AA7075 alloy; semi-solid processing; thixocasting; tensile fracture behavior; tensile properties