Role of synergistic hardening and damage evolution on the stretchability of Al1050/steel/Al1050 sheets

The configurational design of heterostructures has received considerable attention to achieve a superior combination of strength and ductility. Although heterostructuring for enhanced tensile properties has been widely analyzed, studies on the effect of heterogeneity on sheet formability are still insufficient. Sheet metal formability is one of the most crucial factors for determining hetero-materials’ industrial utilization. To broaden the industrial applicability of heterostructured layered materials, investigating the effects of heterogeneity in the layered structure on formability is necessary. This study investigated the stretch formability of aluminum-steel-aluminum clad sheets using the Erichsen cupping test. The three-layered clad sheets showed additional hardening with a slight increase in ductility owing to hetero-deformation-induced hardening because the strain-hardening exponent has a linear relationship with stretchability or necking resistance. After necking, damage evolution owing to severe internal stress concentration led to delamination at the interface. Interestingly, delamination serves as a block to full cracking through the thickness during forming. This study contributes to the industrial applicability of heterogeneous structuring by elucidating the characteristics of heterogeneity and formability.