Effect of scandium content on the hot extrusion of Al-Zn-Mg-(Sc) alloy

The effects of scandium content and extrusion parameters on Al-Zn-Mg-(Sc) alloys were examined. Three kinds of Al-Zn-Mg-(Sc) alloys with up to 0.30 wt.% Sc were prepared. DSC analyses and hot compression tests were conducted to investigate the melting temperature and the microstructure evolution during hot deformation. The addition of 0.1 wt.% Sc into AA7075 was not enough to provide sufficient nucleation sites for dynamic recrystallization. On the other hand, the addition of 0.30 wt.% Sc resulted in significant grain refinement and fully equiaxed microstructure. Despite of microstructural differences in the alloys, thermal and deformation behaviors were very similar. After extrusion at 350 degrees C with the ram speed of 15 mm/s, AA7075 showed a moderate surface quality compared with other Sc containing alloys, which was attributed to low flow stresses. AA7075 showed coarse-grained bands in surface region. With the ram speed of 1.5 mm/s at 350 degrees C, the surface quality of the alloys was sound due to low friction stresses and deformation heating. As the Sc content increased, tensile strengths and elongations at room temperature improved. (c) 2006 Elsevier B.V. All rights reserved.