セミソリッド連続鋳造で作製された６０７０および７０７５アルミニウム合金のチクソフォーミング特性

Abstract

To compare the thixoformability between granular crystal structures and dendrite crystal ones of 6070 and 7075 aluminum alloy billets produced by the semisolid and conventional DC continuous casting, the thixoforming test was performed at a constant deformation speed of 4mm/s in an argon atmosphere. The test piece consisting of granular crystals of 6070 alloy reveals that the thixoforming power was less than 1 kN during three quarters of forming process and the maximum power at the final stage was 18kN. In contrast, the test piece consisting of dendrite crystal structure reveals that the power was more than 5 kN at the first stage and as the forming process proceeded, the power increased. The maximum power at the last stage was 35 kN. Granular grains of primary α aluminum coexisting with the liquid phase were possible to move easily into the die cavity, because the liquid phase played an important role of lubricant as the thixoforming was performed to the semisolid slurry. However, when dendrite network was developed throughout the billet, the liquid phase among interdendrites only moved at the first stage. Hence, the deformation resistance increased and the thixoforming power became larger at the later stages. The same results were obtained by the thixoforming of 7075 aluminum alloy.