Influence of aging on corrosion behavior of 2195 Al-Li alloy

Intergranular corrosion and exfoliation corrosion behavior of 2195 Al-Li alloy with different aging treatment schemes were studied. The results show that the naturally-aged 2195 alloy has the best intergranular and exfoliation corrosion resistance. The intergranular and exfoliation corrosion are accelerated with prolonging the increasing aging time at 160 ℃, which is in accord with the results of polarization tests in IGC solution. Microstructure observations show that the main precipitate of 2195 Al-Li alloy is T_1 phase. With the aging time increasing, T_1 phase coarsens, and precipitate-free-zone(PFZ) and equilibrium phases are observed along grain boundaries. It is shown by open-circuit potential measurements that the open-circuit potentials of PFZ and T_1 phase are more negative than that of Al matrix. They act as anodes in corrosive media and dissolve preferentially. These cause the intergranular and exfoliation corrosion of 2195 alloy. Compared with the peak-aged alloy, the over-aged alloy contains more equilibrium phases at the grain boundaries and wider PFZ, and thus suffers from faster intergranular and exfoliation corrosion.