Papers by Author: Tomoya Omura

Abstract: In this study, asymmetric warm rolling (AWR) has been applied to improve the formability of bake-hardenable Al-3mass%Mg-1mass%Cu-(Ag) alloy sheets. The T4 sheets by the AWR are superior to those by conventional rolling (CR) in Lankford value and drawability. This improvement is caused by a change in the recrystallization texture to have a predominant orientation close to {111}//ND. The unusual texture for recrystallized aluminum alloy sheets is due to the shear deformation introduced during AWR. The Al-Mg-Cu alloy sheets by AWR have been confirmed to possess combined bake-hardenability and the improved formability. However, the bake-hardening response of the Al-Mg-Cu alloy by AWR is slightly inferior to that of the identical alloy by CR.

Abstract: In this work, the bake-hardening (BH) response of an Al-3.0Mg-1.0Cu (in mass%) alloy has been improved by the small addition of Ag as a good example of our proposed Nanocluster Assist Processing (NCAP) technique. From the detailed observation through high resolution transmission electron microscopy (HRTEM), it is found that the origin of the increased hardness in the Ag-added alloy is attributed to the densely and uniformly formed Z phase at the expense of Guinier-Preston- Bagaryatsky (GPB) zones and the S’ phase. It is new findings that the Z phase is formed even in the ternary alloy although the chemical composition lies in the (α+S+T) phase field. Based on the threedimensional atom probe (3DAP) results, furthermore, it is suggested that nanoclusters of Mg, Ag and/or Cu provide effective nucleation sites for the Z phase, whereas nanoclusters of Mg and Cu do less. Such unique characteristics of Ag are clearly seen in the newly constructed interaction energy map (IE map).