Effect of scandium on the hot extrudability of 7075 aluminum alloy

This study investigated the effect of the addition of scandium on the hot extrudability of 7075 alloys. Three kinds of Al-Zn-Mg-(Sc) alloys with up to 0.30 wt.% Sc were prepared, including 7075 aluminum alloy without Sc (AA7075). Differential scanning calorimetry (DSC) analyses and hot compression tests were conducted to examine the incipient melting temperature of the alloys produced. The addition of 0.30 wt.% Sc resulted in significant grain refinement and a fully equiaxed microstructure. Hot compression tests were conducted to determine the critical damage values based on Cockroft-Latham criterion. Then, the surface quality of an extruded bar of each alloy was simulated with a finite element code. The surface condition of an extruded bar was predicted and compared with the experimental results. After hot extrusion, AA7075 without the addition of Sc showed a more moderate surface quality than the alloys modified with Sc. However, AA7075 revealed coarse-grained bands just below the surface area. Extrusion limit diagrams were constructed for the three alloys.