Breakthrough the strength-ductility trade-off in AA7075 alloy by gradient microstructure

In this research, AA7075 aluminum alloy cladded with pure aluminum was processed by compression bonding at three different temperatures. The AA7075 layers in the compression-bonded samples revealed a gradient microstructure through the thickness. The grains near the interfaces of pure Al/AA7075 were significantly elongated (hard domain), while the grains in the midthickness of AA7075 layers were slightly elongated (soft domain). The bonding quality between pure aluminum layers was improved with the increase in the compression bonding temperature. The characteristic peaks of α-aluminum in the compression-bonded sample at 25 °C shifted to the right owing to the cold plastic deformation. By increasing the compression temperature from 25 to 200 °C, the shift value was decreased due to the occurrence of dynamic and static recovery. By increasing the temperature of compression bonding from 25 to 200 °C, the texture parameter value of recrystallization texture was decreased from ~ 2.6 to ~ 1.4, while the texture parameter of deformation texture was increased from ~ 1.8 to ~ 4.1. A texture transition from recrystallization texture to deformation texture occurred by increasing the compression temperature. By increasing the compression bonding temperature from 25 to 200 °C, the hardness and strength of samples were reduced owing to the promotion of dynamic and static recovery. Interestingly, the strength, ductility, and toughness of the compression-bonded sample at 200 °C were increased simultaneously compared to the as-received alloy. Introducing gradient microstructure in the AA7075 layer could overcome the trade-off of strength and ductility, and as a result, toughness was enhanced significantly. By increasing the temperature of the compression bonding process from 25 to 200 °C, the number and size of dimples were increased and a transition in fracture mechanism from intergranular to transgranular ductile fracture occurred.