Cyclic material behaviour of magnesium die castings and extrusions

Abstract

An increasing number of components are designed by using the local strain concept. This concept is commonly used for many different materials. The question is, can the local concept be used for components made of magnesium alloys? Therefore the material behaviour must be described and the material properties need to be adequate. The main topic of the present investigations is the verification of the Masing and memory behaviours. These two material properties are necessary for the component design by the local strain concept. Therefore the cyclic deformation behaviour is investigated in strain controlled tension compression tests. The magnesium die casting alloys AZ91 and AE42 and the magnesium extrusions AZ31 and AZ80 are tested. The magnesium die castings show approximately Masing behaviour, but the hysteresis of magnesium differs from the hysteresis of steel. All investigated magnesium alloys show the material memory M2. The magnesium extrusions show a totally different behaviour in tension and in compression. The hysteresis in experiments differs from the calculated hysteresis for the cyclic stress–strain curve. The Masing behaviour cannot be observed because of the strong anisotropic behaviour in tension and in compression direction. The calculation by the local strain concept cannot be used for the investigated magnesium extrusions without modifications because the hysteresis in tensile and in compression direction is very asymmetric. The cyclic stress–strain curve of the extrusions can only be described approximately by the Ramberg–Osgood equation.