THE CONCEPT OF THE FATIGUE POTENTIAL OF CAST ALLOYS

Abstract

The cumulative failure distributions of fatigue life of cast alloys is shown to be characterised by a number of distinct platforms and steps. A technique to demonstrate the existence of an ultimate step has been discovered. This illustrates for the first time that some current cast aluminium alloys are, at best, only achieving 1% of their potential fatigue life. If the materials are subjected to poor casting techniques the fatigue life performance is expected to fall further. It is therefore concluded that by a combination of attention to metal quality and casting technique, the fatigue lives of most Al alloy castings can probably be improved by a factor of 100 to 10,000 times. It is speculated that the huge numbers of double oxide films which appear to be present in liquid aluminium and control the properties of castings will survive to be present in most wrought products and similarly control the failure behaviour throughout the greater part of aluminium metallurgy.