Effect of grain size on stress corrosion cracking behavior of LY12 alloy

The stress corrosion cracking(SCC) behavior of LY12 alloy with coarse-grained layer was investigated in 3.5 % NaCl+0.5 % H₂O₂ solution by constant load stress corrosion test. Electrochemical impedance spectroscopy (EIS) of the LY12 alloy with and without coarse-grained layer was studied. The microstructure and fracture morphology were observed and analyzed by 3D-cubic microscope and scanning electron microscope (SEM). The grain size of surface layer coarse-grain zone and the inner layer fine zone of this alloy were calculated too. The results show that the grain size of coarse grain grade is 5.88, while that of inner zone is 12.71. Because grain size of coarse-grain layer is bigger than the inner zone, the big size grains can protect the LY12 alloy from stress corrosion cracking and remarkably decrease the susceptibility of alloy from SCC in 3.5 % NaCl+0.5 %H₂O₂ solution. The impedance of the alloy with coarse-grain layer is 2 500 Ω; after removing the coarse-grain layer, the impedance declines to 2 000 Ω. Consequently, coarse-grained LY12 alloy has a better SCC resistance in 3.5 % NaCl+0.5 %H₂O₂ solution.