Hot cracking tendency of foundry alloys – an innovative testing method

The results of testing the tendency of light metals to forming defects from the group of discontinuities - hot cracks (W-301) [1], are presented in the hereby study. These are alloys of a small or moderate tendency for hot cracking. However this tendency is growing when castings are produced in metal moulds or have large dimensions. The majority of investigation methods, developed several years ago, does not provide the possibility of the total assessment of alloys. This convinced the authors to develop the new method and to build the new research set-up in the Faculty of Foundry Engineering AGH. This new set-up makes possible to perform measurements of stresses growing in the sample (casting) in the real time - during the whole period of solidification and cooling. The measurements allowed to determine the moment in which the initiation, followed by the propagation, of cracks occurs as well as to find out at what thermal stress the casting discontinuity forms. Due to this, the complete image of the defect formation is obtained. The results of investigations performed for the casting alloy AlSi7Mg (A356), which is widely applied in the automotive and aircraft industry for drive gear housings, are presented in the hereby study. This alloy is characterised by a low hot cracking tendency.

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