Strain-induced Texture Development in the Magnesium Alloy Az31

Magnesium alloys are receiving increasing attention as a structural material in vehicles to reduce weight and increase fuel economy. Understanding the formability of lightweight alloys is one key to their successful introduction in vehicles. We present results of X-Ray diffraction and electron back-scatter diffraction texture measurements in as-cast and uniaxially compressed AZ31 for a variety of strains, strain rates and temperatures (0.2 to 1.0, 0.01s to 1.0s, 623K to 673K, respectively). Pole figures show that all the samples are dominated by large grains, even those that have undergone very large deformations. In order to understand the trends in texture, it was necessary to average results from multiple sample sections to overcome the poor statistics of the coarse grained samples. Our results indicate that the expected basal texture develops at very low strains (<0.4) and remains essentially unchanged at higher strains (0.4 1.0). INTRODUCTION The continuous push to higher vehicle fuel economy will require improvements in both powertrain technology, aerodynamics and weight reduction. Magnesium alloys offer an opportunity to achieve significant weight reductions when compared to steel or aluminum, while maintaining high strength compared to polymers. To enable reliable engineering choices that maintain materials properties, a predictive tool is needed. At Ford, we are developing a Integrated Computational Materials Engineering (ICME) tool that incorporates materials chemistry and thermodynamics with processing parameters (casting conditions, forming operations, heat treatments) to predict material strength, fatigue resistance and ductility. To develop the tool, empirical measurements of processed materials, as well as computational data from first-principle calculations (e.g., Density functional theory estimations of formation enthalpies) and finite-element simulations are used to refine weights in the engineering decision trees. There are various techniques which can measure grain orientation texture, including Electron Backscatter Diffraction (EBSD), neutron diffraction and X-ray diffraction (XRD). EBSD provides micron-scale lateral spatial resolution but is only sensitive to nanometer depths. This feature presents a significant challenge to studying alkali and alkaline-earth metals due to their rapid oxidation, where surface oxides less than 10nm thick can obscure the electron diffraction arcs. In addition, for large grained materials, EBSD can be very cumbersome, since large areas need to be scanned to develop a statistically meaningful average of the volume-weighted orientation distribution function, resulting in long acquisition times. Neutron diffraction solves the problems of sample preparation and sampling by using diffraction from a large volume (cm) 71 Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 2