The 7000 series aluminum alloy has high strength and it is expected as a material with large weight saving effect in the field of transport including automobiles. However, extrusions sometimes generate coarse recrystallized grains on their surfaces. In particular for 7000 series alloy, these coarse grains may decrease the resistance for stress-corrosion cracking, resulting in potential failure in practical use. For this reason, transition elements have generally been added to 7000 series alloy, and the dispersoids composed of these transition elements suppress the coarsening recrystallized grains. As transition elements added to practical alloys, Mn and Zr are often selected. Some papers report that the addition of transition elements sharpens quench sensitivity, and thus often decreases its strength [1-4]. Therefore, it is important for structural materials, to quantitatively investigate the effect of the addition of transition elements on the strength of extrusion. In this study, the effects of Mn and Zr on the recrystallization suppression effect and strength in 7000 series aluminum alloy have been investigated. It was found that Zr has larger effect on recrystallization suppression than Mn. In addition, it was found that as the addition of Mn increased, quench sensitivity sharpened, resulting in larger reduction in strength. On the other hand, Zr addition hardly gave effect on quench sensitivity. From these results, it became clear that Zr addition is preferable than Mn addition from the viewpoints of recrystallization suppression and strength.
