Microstructural, texture and residual stress investigations on a twin roll cast AZ31 magnesium alloy

Magnesium alloys are interesting for both structural and functional applications where the mass of components is of concern. For the production of panels or frames whose shape develops mainly according to a 2-D configuration, a sheet forming sequence may be considered rather than pressure die casting, squeeze casting or thixotropic casting. An interesting method to obtain semi-finished sheets is twin roll casting. The rolled-cast sheet usually requires further rolling to achieve the required thickness. Aim of the work is the characterization of a piece of “as twin roll cast” AZ31 sheet. To this end usual microstructural investigation techniques were used, such as light and scanning electron microscopy, energy dispersive spectrometry and X-ray emission maps, in association with crystallographic texture determination by X-ray diffraction and residual stresses determination by means of the Hole-Drilling Strain-Gage Method. The investigations showed an heterogeneous distribution of structural components associated with an inhomogeneous distribution of residual stresses through the thickness of the sheet. This confirms the absolute necessity to carry out effective solution treatments before performing any further reduction of the thickness of the sheet by hot rolling or whatsoever forming step aimed at achieving the required final configuration of a workpiece.