Subgrain development in hot working of Al and Al-5Mg

Over the range 400-500 degrees C at 1.16 s(-1), Al flow curves exhibit monotonic hardening to attain, by strains of 0.9-2.8, true steady states. The elongated helicoidal grains were observed on planes normal to the radius by both SEM-EBSI and by TEM. The equiaxed subgrain sizes in Al exhibited a log normal distribution, as temperature rises, the mean and S.D. rise so that the distribution widens considerably at the upper end. In contrast for Al-5Mg, the flow curves rise to a peak and decline slowly at a diminishing rate, the maximum strength is about four times that of Al. In TEM, the dislocations are in long planar arrays at epsilon = 0.2 whereas the SEM-EBSI indicates only indistinct distortions. At 0.45 the subgrains are very elongated. At 1.8 and 2.8, the subgrains are equiaxed at 1.4 mu m, being about 1/3 that of Al (similar to 3.9 Gun). (C) 1997 Elsevier Science S.A.