New materials in the Al-Zn-Mg-Cu-La alloy system have been proposed for improving corrosion resistance in a study by Kishi et al, because Lanthanum, La, has a storage capability for hydrogen. Hydrogen is a problem in the stress corrosion cracking (SCC) growth mechanism. Zinc, Zn, Magnesium, Mg, and Copper, Cu, in the alloy have influenced the extrusion, strength and other properties; however, in the case of putting this material to use, it is also necessary to evaluate it from the viewpoint of fracture mechanics. The stress intensity factor, K, obtained from fracture mechanics is a necessary parameter for the evaluation of various materials.
The first part of this study deals with the measurement of fatigue crack growth in the Al-Zn-Mg-Cu-La alloy system. The second part evaluates the fracture surface obtained from tests of these materials by the application of x-ray fractography.