Abstract
The influences of bending and torsional loading modes on the crack initiation behavior in static and cyclic stress corrosion cracking (SCC) were investigated on a high-strength aluminum alloy sensitive to active path corrosion type SCC. Static and cyclic SCC cracks were found to be initiated under torsional loads as well as under bending loads, and cyclic SCC lives were smaller than those of static SCC irrespective of loading modes. Under bending loads, cyclic SCC cracks in a high stress region were initiated at corrosion pits at three adjacent grain boundaries. In a low stress region, cracks were initiated at longitudinally dissolved trenches along grain boundaries in a similar way to static SCC. Under torsional loads, on one hand, cyclic SCC cracks in a high stress region were initiated at the longitudinal slip dissolution. In a low stress region, the life lines were divided into the longer and the shorter lines according to the types of initiation sites; on the longer life line, cracks were initiated at longitudinal slip dissolution, whereas on the shorter life line, cracks were initiated at the sites including intergranular dissolution. For static SCC, cracks were initiated at longitudinally dissolved trenches along grain boundaries. The longitudinal dissolution along grain boundaries under bending and torsional loads as well as longitudinal slip dissolution under torsional loads is considered to be caused by shear stresses.
