Effects of Zn element and aging process on local corrosion behavior of 2056 aluminum alloy

The effects of Zn element and aging process on intergranular corrosion resistance and exfoliation corrosion resistance of 2056 aluminum alloy were investigated by intergranular corrosion(IGC) experiments,exfoliation corrosion(EXCO) experiments and transmission electron microscopy(TEM) and scanning electron microscopy(SEM). The results show that the intergranular corrosion and exfoliation corrosion susceptibility reduce gradually with further aging at T6 temper(175 ℃) for 2056 aluminum alloy. At T3 temper(room temperature) and peak-aging T8 temper(155 ℃),intergranular corrosion resistance and exfoliation corrosion resistance of 2056 aluminum alloy improve a lot,while the alloy possesses the best corrosion resistance at T3 temper. 2056 alloy with Zn addition has a better corrosion resistance at peak-aging T6 temper than the alloy without Zn addition. Local corrosion resistance is closely related with the grain boundary and the adjacent periphery. When the precipitation of equilibrium phases along the grain boundaries distributes continuously and the precipitate free zone(PFZ) is wide,the 2056 Al alloy possesses high intergranular corrosion and exfoliation corrosion susceptibility. When the alloy possesses larger size of precipitation of equilibrium phases along the grain boundaries and narrower PFZ,the alloy will achieve better intergranular corrosion resistance and exfoliation corrosion resistance. When there is nothing around the grain boundaries,the alloy has the best corrosion resistance.