CORROSION-FATIGUE OF AZ91E-T6 CAST MAGNESIUM ALLOY IN A 3.5 PERCENT NACL AQUEOUS ENVIRONMENT

The objective of this research was to obtain and compare constant and variable amplitude fatigue behavior of AZ91E-T6 cast magnesium alloy i n both an air and 3.5 percent NaCl aqueous corrosive environment. An a dditional objective was to determine if commonly used models that desc ribe fatigue behavior and fatigue life are applicable to this material and test environment. Fatigue tests included constant amplitude strai n-controlled low cycle fatigue with strain ratio, R, equal to 0, -1 an d -2, Region II constant amplitude fatigue crack growth with load rati o, R, equal to 0.05 and 0.5 and variable amplitude fatigue tests using keyhole notched specimens. In all fatigue tests, the corrosion enviro nment was significantly detrimental relative to the air environment. M ean strains influenced fatigue life only if accompanied by significant mean stress. The Morrow and Smith, Watson, and Topper mean stress mod els provided both accurate and inaccurate fatigue life calculations. L ikewise, variable amplitude fatigue life calculations using the local strain approach and based upon the formation of a 1 mm crack at the ke yhole notch were both accurate and fairly inaccurate depending on the specific model used.