Recrystallization kinetics and grain growth studies in twin-roll cast strips of commercial purity aluminium (1050) and aluminium-magnesium alloy (5005)

Abstract

Recrystallization kinetics and grain size distribution have been studied in commercial purity aluminium (1050) and Al-Mg alloy (5005) which had been previously twin-roll cast to thicknesses of 1.5 mm and 3 mm. The samples were annealed at 300 °C for different times up to 20 hours. The index of recrystallization was found to be 3.2 ± 0.2 for each type of material, which implied a three-dimensional nature of recrystallization. The 1.5 mm thick samples had higher nucleation rates and, therefore, a smaller final average recrystallized grain size. The grain size distribution was more stabilised in the 1050 samples than in the 5005 samples, and this may be due to the drag effect of the FeAl3 particles on the grain boundaries in the commercial aluminium samples. The degree of spread in the distribution of the grain sizes was bigger in samples rolled to 3 mm than those rolled to 1.5 mm. Anisotropy in the microstructure was observed in the 1050 sheets of thickness 3 mm, in that, the average grain size in the rolling direction (RD) was larger than that in the transverse direction (TD). However, during annealing at 500 °C, the 1.5 mm-thick samples of the 1050 sheet preceded the 3.0 mm-thick samples in achieving an equiaxed grain structure.