新規の中間加工熱処理と7475合金の超塑性

抄録

7475 alloy plates were cold rolled into sheets 1.6mm in thickness at a rolling reduction 73%, recrystallized and solutionized at 480°C at different heating and cooling rates, and were finally cold rolled to 1.2mm thickness. Tensile tests under an increasing temperature condition or hot tensile tests after warm prestraining were performed. The sheets rapidly heated and rapidly cooled in the intermediate heat-treatment show superplastic elongation 500% or more under an increasing tempuature condition and at a strain rate 2.8×10^-3/s which is one order of magnitude higher than that informed for intermediate thermomechanically treated 7475 sheets up to date. The same sheets prestrained by 15 to 30% at about 360°C also show superplasticity at the hot tensile tests. Fairly fine but elongated grains containing considerably fine subgrains 2 to 10μm in diameter are developed by ITMT and the warm prestraining. These subgrains would play a vital role during superplastic deformation.