RECRYSTALLIZATION KINETICS IN ALUMINIUM-ALLOYS

Abstract

Studies on recrystallisation behaviour have been conducted on en Al-1.35 weight percent Mn alloy at various deformations (90 percent, 40 percent, 10 percent) and annealing temperatures, using light microscopy and hardness measurement techniques. At 90 percent deformation, recrystallization occurs by nucleation and growth of strain free grains at all tenperaturee. At 40 per- cent and 10 percent deformations recrystallization also occurs by the movement of already existing grain boundaries (strain induced grain boundary migration) provided annealing is carried out at low temperatures (300°0 for 40 percent deformation and 400°0 for 10 percent deformation). At higher temperatures, no movement of original grain boundaries is observed. The experimental data . fit very well to the Avrami relation of the type X e -Bt But, the metallographic studies on the geometry of the recrysta-Weed grains are notAf in ull agreement with the value of k determined from the above equation. Moreover, it is also seen that during annealing at any temperature the value of k changes abruptly after a specific annealing interval. The aotivation energy for the recrystallisation at 90 percent deformation is calculated to be 38 4. 1 KcalatMole which is quite aloes to that for the diffusion of Manganese in Aluminium matrix. Wetallographic studies have shown that the grain size increases parabOlically with annealing time at all temperatures. Grain growth rate is higher, higher the annealing temperature. Results have been discussed in terms of the various driving forces for racrystalliaation, the occurrent* of precipitation reaction and the diffusion of Manganeee atoms in the Aluminium