Microstructure evolution and mechanical properties of backward thixoextruded 7075 aluminum alloy

The present work deals with the microstructure evolution of 7075 aluminum alloy which has been backward thixoextruded in the temperature range of 550–600 °C using different ram diameters and ram displacement velocities. The recrystallization and partial melting (RAP) route has been used to obtain the semi-solid feedstocks for thixoforming. The results indicate that the back extruded microstructures mostly consist of semisolid grains which have been elongated along extrusion direction. The finest semisolid grain size has been obtained at lower deformation temperature and higher equivalent strain. This is attributed to the higher imposed shearing force on the liquid phase which could in turn fragment the grains. The current work also explores the room temperature mechanical properties of thixoformed work-pieces using shear punch testing method. It is found that the room temperature shear strength and ductility values have been substantially influenced by the deformation temperature, ram displacement velocity, and ram diameter.

► Fully spheroidal microstructures were obtained on preheating of as-extruded material.
► Deformation parameters affected final semisolid grain sizes.
► Lower strength and higher ductility by the higher backward thixoextrusion temperature.
► Increasing the ram velocity enhanced room temperature strength and ductility.
► Increasing the punch diameter reduced the ductility values.