Abstract
The 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 213×103 to 1016×103 cycles following adoption of the bottom tapping technique. Hipping of the bottom tapped castings produced a further increase in the average life to at least 15×106 cycles. 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
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