Microstructure and Properties Evolution Mechanism of AA7020 Twin-Roll Cast Sheets with Different Zirconium Contents

AA7020 sheets with different Zr contents were successfully fabricated by twin-roll casting process. In order to investigate the effect of Zr content on AA7020 twin-roll cast sheets, the microstructure and mechanical properties were detected by optical microscope, scanning electron microscope, transmission electron microscope, hardness tester and universal testing machine. The results show that proper addition of Zr content can effectively improve surface cracks, refine grains, and mechanical properties of twin-roll casting sheet. Zr mainly exists in the form of Al₃Zr in aluminum alloy. With increasing of Zr content, Al₃Zr phase tends to aggregate, even become potential cause of crack formation at 0.83% of Zr content. When the content of Zr is 0.33%, the comprehensive properties of AA7020 twin-roll cast sheets reach an idea value, i.e., yield strength 234.9 MPa, tensile strength 254.3 MPa, elongation is 10.8%, and hardness 176 HV.