The Effect of Mg Content on Intergranular Corrosion of Al-Mg-Mn Alloys after Annealing

Abstract

The Intergranular Corrosion (IGC) properties of Al-xMg-0.6Mn (x=3, 4, 5, 6 and 7) wt.% alloys were studied using the mass loss test. The mass loss test results of the alloys annealed at 100-300 ̊C for 1h indicated that the alloys with 3 and 4% Mg were resistant to IGC. While the mass loss values of the 6 and 7% Mg alloys were increased to IGC severe sensitive region, and then abruptly fallen to the IGC-resistant region with the increasing temperature. The mass loss-temperature curve of 5% Mg alloy was actually located between them. After isothermal annealing, the mass loss results indicated a stabilization temperature of the alloys with 5, 6 and 7% Mg appeared at the temperature beyond 220 ̊C, 250 ̊C and 270 ̊C, respectively. Furthermore, below the stabilization temperature 10-20 ̊C, it was observed a type of “special mass loss curve ” in so-called transition region that was showed a quick mass loss increasing to sensitization region and then a decrease to the IGC resistant region with a prolonged annealing time. To explore the “special curve” in transition region, the TEM observation of Al-7Mg alloy annealing at 250 ̊C was conducted, which indicated the sensitization resulted from the continuity of β phase, while the descending to the IGC might to be attributed to the spheroidization of β phase.