Heterogeneity and Homogeneity in 2/4 N Multilayered Al Fabricated by Accumulative Roll Bonding and Annealing

Abstract

Multilayered Al sheets having alternative stacking of 2 N Al (99.21 wt.% purity, N is short for nine) and 4 N Al (99.993 wt.% purity, N is short for nine) with various layer thicknesses from 16 to 1 μm were fabricated by 6 to 10 accumulative roll bonding (ARB) cycles, followed by annealing. The effects of layer thickness and annealing treatment on mechanical properties were studied. In all samples, the grain sizes in the 4 N layers were larger than those in the 2 N layers due to the purity difference. The grain size and mechanical properties saturated after 6 ARB cycles, but the layer thickness gradually decreases with increasing cycles and accordingly, more homogeneous microstructures were obtained with higher cycles. After annealing, heterogeneous structures were retained in 6-cycle sample, while most homogenous structures were observed in 10-cycle sample. Yield-drop phenomenon widely observed in the homogeneous samples disappeared in the heterogeneous 6-cycle sample after annealing at 225 and 250 °C.