Simultaneous improvement of strength and toughness in Al-Zn-Mg-Cu/pure Al laminated composite via heterogeneous microstructure

In the present study, high-strength and high-toughness Al-Zn-Mg-Cu/pure Al laminated composite with a heterogeneous microstructure were manufactured by the compression bonding process. Two three-layer and four-layer samples were fabricated via compression bonding at 200 degrees C with 30% and 45% thickness reductions, respectively. Bonding lines were observed on the interfaces of the three-layer sample. However, no clear bonding line was seen at the interfaces of the four-layer sample, indicating strong bonding between layers. The recrystallization texture was dominated in the as-received and solution-treated samples. However, a texture transition from recrystallization to deformation texture has occurred in both three-layer and four-layer samples. The hardness distribution of processed samples was heterogeneous. The hardness of the inner Al-Zn-Mg-Cu layers was lower than that of the outer Al-Zn-Mg-Cu layers for both three-layer and four-layer samples. Interestingly, both strength and toughness were remarkably increased in the four-layer sample compared to the as-received alloy, while ductility remained almost unchanged. The four-layer sample exhibited a three-stage strain hardening behavior due to the mechanical properties contrast and resultant strain partitioning of the heterogeneous microstructure. However, the three-layer sample did not enter the third stage of strain hardening due to the weak bonding between the layers. The extent of delamination of the three-layer sample was very large (complete debonding) owing to the weak bonding between the layers. In contrast, the interfaces of the four-layer sample after fracture did not completely separate, indicating that the four-layer sample has good interfacial bonding. Both samples revealed a heterogeneous fracture behavior.