The effect of quench rate and overageing temper on the corrosion behaviour of AA7050

Pitting corrosion of naturally aged AA 7075 aluminum alloys with bimodal grain size

“…Both anodic and cathodic Tafel slopes (b a and b c ) increased with the increasing ratio of fine grains, implying that both the anodic and cathodic reactions of corrosion were retarded on fine grains. The b a in this work was far bigger than the values of 20-30 mV/dec caused by aluminum oxidation to Al 3+ [9,43], this could be attributed to the passivation of alloys. The b c also showed higher values than the cathodic reactions controlled by oxygen reduction (about 120 mV/dec) [9,[44][45][46][47].…”

“…For example, Al-Zn-Mg-Cu series alloys are widely used in aerospace industry because of their low density and high strength, but they are very susceptible to localized corrosion, such as pitting, intergranular corrosion (IGC) and exfoliation corrosion (EXCO). Both the anodic particles (usually containing Al, Zn and Mg) and the cathodic particles (usually containing Al, Fe, Cu and Mn) can induce pitting corrosion, because they exhibit different electrochemical activity and passivation ability compared to the surrounding matrix [7][8][9][10].…”

Mechanism of low exfoliation corrosion resistance due to slow quenching in high strength aluminium alloy

“…Moreover, it was found precipitates free zones (PFZs) adjacent to grain boundaries may play an important role. Wide PFZs may increase the susceptibility to intergranular corrosion [27]; depletion of Cu within PFZs was believed to be the primary reason for the increased resistance to stress corrosion cracking of 7075 alloys after T73 and retrogression and re-aging treatments [28].…”

“…For alloys with a high Cu concentration, the decrease of quench rate often leads to lower resistance to intergranular corrosion, exfoliation corrosion and stress corrosion cracking [3,27,[29][30][31]; but for alloys with a low Cu concentration, the decrease of quench rate seems to increase resistance to stress corrosion cracking [25,32]. For a 7085 aluminium alloy forging, it was shown that the content of Zn and Cu in GBPs decreased with the decrease of quench rate, and the low content of Cu in GBPs was supposed to be the reason for the worst resistance to stress corrosion cracking of the slowly quenched specimens [31].…”

Critical quenching rate for high hardness and good exfoliation corrosion resistance of Al-Zn-Mg-Cu alloy plate

“…The decrease in quenching rate also tends to decrease localized corrosion resistance, which is closely related to the changes in the microstructure and microchemistry of GBs. After slow quenching, the grain-boundary particles (GBPs) often become larger with greater interparticle spacing, and precipitate-free zones (PFZs) near GBs become wider; however, the content of Zn, Mg, and Cu in the GBPs may increase, decrease, or remain constant [5,[13][14][15][16], which seems to be dependent on the compositions of the studied alloys or the range of quenching rates. The complex effects of these microstructural and microchemical features on the localized corrosion resistance have recently been discussed in detail [5].…”