AbstractThe fatigue properties of Al-1OMg (wt-%) castings have been shown to be improved by hot isostatic pressing (hipping) with a level of improvement highly dependent on the initial quality of the castings. Only castings with low oxide inclusion levels were found to show a significant improvement infatigue propertiesjollowing hipping. To reduce the oxide inclusion content a casting technique has been developed in which the molten aluminium is tapped from the bottom of an induction melting furnace. The average fatigue life (at a test stress amplitude of 106 MN m−2) increased from 213×103to 1016×103cycles following adoption of the bottom tapping technique. Hipping of the bottom tapped castings produced a further increase in the average life to at least 15×106cycles. These substantial improvements in fatigue properties can be attributed to a reduction in the size and quantity of oxide inclusions in the bottom tapped castings. Unless the oxide inclusion content of the castings can be maintained at a sufficiently low level the optimum properties will not be obtained after hipping and the repeatability in the mechanical properties of hipped castings, necessary for confidence in design, will be poor.MST/3186