EFFECT OF COPPER CONTENT AND DEGREE OF RECRYSTALLIZATION ON THE FATIGUE RESISTANCE OF 7XXX-TYPE ALUMINUM-ALLOYS .1. LOW-CYCLE CORROSION FATIGUE

The effect of copper content (0.01-2.1%) and degree of recrystallization (DR) (5-45%) on the corrosion fatigue behavior of four AlZn2MgxCuT651 alloys was investigated. The cyclic strain resistance was found to increase with copper content and decrease with DR regardless of the test environment. This trend is more pronounced in aggressive environments. The improved fatigue resistance is attributed to the increased homogeneity of slip as the copper content is increased and the DR is decreased. The environmental sensitivity, which increases with decreasing copper content, is dependent on slip behavior. For alloys tested in distilled water hydrogen embrittlement is believed to be the major factor controlling the low cycle corrosion fatigue. For tests conducted in a 3.5% NaCl solution hydrogen embrittlement still plays an important role but the preferential dissolution and/or adsorption process may also have a detrimental effect. © 1979.