Synthesis of gradient thin films by ion-beam-enhanced deposition: Liu, X. Zou, J., Zhou, S., Taniguchi, S., Schroer, A. and Wolf, G.K. Mater. Sci. Eng. A July 1991 A139, (1–2), 220–224

Abstract

The effects of test temperature, stress intensity factor, sodium impurity content and aging condition on the short transverse sustained-load (creep) cracking of AlLiCuMgZr 8090 alloy plate have been studied. Creep cracking was orders of magnitude faster, and threshold stress intensity factors were much lower, than for conventional aluminium alloys such as 2014-T651. Significant rates of cracking were observed in alloy 8090 at temperatures as low as 60 °C at stress intensity factors as low as about 5 MPa m12. For a given stress intensity factor, cracking rates were similar for underaged, peak-aged and overaged conditions but were higher for alloys with higher sodium impurity levels. Metallographic and fractographic observations suggest that the presence of liquid sodium-rich impurity phases promote creep cracking in alloy 8090. Creep cracking in conventional aluminium alloys is probably promoted by solid impurity phases such as lead which are less mobile and therefore less damaging than sodium-rich phases.