Study Of Corrosion Behavior Of High Strength Aluminum Alloy ZL205A Casting

ZL205A high strength aluminum alloy with high specific strength, goodstability (in normal environment) is widely used in manufacturing of a certaintype of strategic missile parts and large aero structures. However, Corrosion ofhigh-strength aluminum alloy in corrosive environments could reduce themechanical properties of components and lead to material failure. Firstly, generalcorrosion behaviors of ZL205A such as pitting corrosion, grain boundarycorrosion, impact of corrosion on mechanical properties, weight loss and generalcorrosion mechanism were analyzed by solution infiltration corrosion test,exfoliation corrosion test, corrosion weight loss test, dynamic corrosion strengthloss Experiments. Secondly the stress corrosion susceptibility of ZL205A wasstudied by SSRT, DCB fracture mechanics testing and C rings Stress corrosiontests.Improved EXCO solution corrosion test of cast ZL205A analysis showed:the beginning2hours are pitting nucleation stage, the pitting corrosion rate is low,in the next2hours, the speed and area of pitting corrosion are both starting toincreasing; Within3hours, the average width of the largest grain boundaries andgrain boundary corrosion are growing rapidly;3hours later, the average width ofgrain boundary corrosion increased slowly, but the maximum width of corrosiongrain boundary still grows; Its General corrosion mechanism is that: Poor copperarea acts an anode forming a large cathode corrosion cell with a small anode andcauses serious corrosion on grain boundaries.Simultaneously, in Cu Al2phase, Albecomes an anodic, Cu can be seen as cathode they forms a corrosionmicro-battery, the corrosion of grain boundary is speeded up by the duplextwo-electrode system. EDS analysis confirmed: The main corrosion products isAl2O3,the same as oxide film. Weight lost experiment in3.5%NaCl Solution showed: in the beginning4hours, the corrosion weight loss rate of cast microstructure is higher than T6microstructure; but within4to8hour, corrosion weight loss rate of castmicrostructure is lower than that of T6. From0to8h, corrosion mass loss rate ofcast structure is still higher than T6ZL205A.Overall, the corrosion resistance. ofT6ZL205A is better than that of cast ZL205A.Dynamic corrosion strength loss Experiments in3.5%NaCl solution showedthat: as to T6ZL205A, the loss of yield strength and tensile strength are both lessthan10%, after96hour it increase to more than10%;the original and corrosionfracture morphology of T6ZL205A are both mixed with cleavage and dimple, thefracture mode is off-type fracture; After96hours, some small simple corrosionzones were found in the edge of fracture; Internal corrosion of alloys begins toform microscopic voids, which can become the source of cracks during stretchingprocess.Exfoliation corrosion tests showed: for T6ZL205A exfoliation corrosiondoes not occur, showing high resistance to exfoliation corrosion; its resistance topitting was assessed as PA level namely its point corrosion resistant is good.SSRT found: the loss of strength and elongation of T6ZL205A in3.5%NaCl solution were less than10%, The ratio of fracture time in two differentcorrosive environment is than91.84%, greater than90%; DCB fracturemechanics testing found: the ratio of KIscc/KICis0.929,which is greater than0.9;After soaking for960hours, in3.5%NaCl solution, No crack was found in the Cring specimens；The above three test results indicated that T6ZL205A has little orno stress corrosion susceptibility.