Effects of Rolling Deformation on Microstructure, Tensile Properties and Corrosion Behaviors of High Mg Alloyed of Al-Mg Alloy

Microstructure evolutions, mechanical properties, intergranular corrosion (IGC), stress corrosion cracking (SCC) and electrochemical corrosion (EC) behaviors of high-strength Al-9.2Mg-0.8Mn-0.2Zr-0.15Ti alloy are carefully investigated by using optical microscope, transmission electron microscopy, scanning electron microscopy and x-ray diffraction (XRD). The as-studied alloys exhibit typical heavily deformed microstructures, with a high density of dislocation tangles, the dense dislocation walls and a mass of fine and dispersed strain-induced precipitates in the severely deformed grains. The ultimate tensile strength, yield strength and elongation of the hot rolled alloy are 625 ± 10 465 ± 2 MPa and 13 ± 1.5%, respectively; the counterparts of the cold rolled alloy are 697 ± 4, 599 ± 2 MPa and 7.5 ± 1%, respectively. The high strength can be mainly owing to dislocation strengthening. The hot rolled alloy shows higher IGC, SCC and EC resistance than the cold rolled alloy. The segregation of Mg atoms at grain boundaries would lead to IGC and the microstructure in ND-RD direction is more vulnerable to the IGC attack. In the process of slow strain rate tensile testing, localized pitting corrosion would be occurred first in 3.5%NaCl aqueous solution. The residual second phases would destroy oxide films during the EC process and accelerate the surrounding matrix corrosion.