Effects of the layer thickness ratio on the enhanced ductility of laminated aluminum

The layered structural parameters have been reported to be critical for tuning the tensile properties of laminated metals. Here, we investigated the effects of the thickness ratio (r_c/f) of coarse-grained layers (CLs) to fine-grained layers (FLs) on the enhanced ductility of the laminated Al. The local strain evolution demonstrates that the strain delocalization ability of laminated Al is improved with the decrease of r_c/f. The interfacial strain gradients, which can produce extra work hardening, gradually approach and cover the CLs with the r_c/f decreasing, explaining the trend of uniform elongation in laminated Al with various r_c/f. The integrated fracture morphology characterization reveals that the increase of the r_c/f leads to an improvement in the tolerance of the interfacial microcracks, which is corresponding to the variation of fracture elongation in the laminated Al. Moreover, there is an evident transition of transverse propagation path of interfacial microcracks from the CLs to FLs with increasing the r_c/f. Based on a geometrical criterion of microcracks connectivity, the preferential transverse propagation path of interfacial microcracks in these laminated Al was rationalized. The calculation based on this criterion also predicted the critical r_c/f corresponding to the optimal combination of strength and fracture elongation. This work deepens the understanding of the role of structural parameters of laminated metals in achieving the strength and ductility synergy.