Improvement of warm formability of Al-Mg sheet alloys containing coarse second-phase particles

Several alloying elements involving Zr, Cu, Zn and Sc were added to Al-Mg sheet alloys in order to obtain an excellent combination of high strength and good high-temperature formability. Microstructural examination showed that coarse intermetallic particles were formed in the microstructure and their amounts changed with variations of the alloying elements. During warm rolling of thermomechanical treatments prior to warm deformation, the coarse particles initiated cracks, decreasing the warm formability. For healing the crack damage and further improving the warm formability, a process of hot isothermal press was developed and optimized to the sheet alloys. With this process, the biaxial stretch formability at 350°C was improved by 22% for an aluminum alloy containing a large amount of coarse particles.