Strain Evolution during Mechanical Loading of the Magnesium Base Alloy LAE442 Studied by means of High Energy Synchrotron Diffraction

Abstract

The highly alloyed wrought Mg-base alloy LAE442 is characterized by a relatively high creep resistance due to secondary phases which are thermally stable. In general the elasto-plastic deformation behavior of Mg-base alloys is due to dislocation slip and twinning depending on the local crystallographic texture with respect to the direction of load application. LAE442 exhibits a rather weak influence of the crystallographic texture after extrusion on the mechanical properties resulting in nearly identical compressive and tensile yield strength values. The relatively high strength of LAE442 is based on a high number of small Al-RE (RE = rare earth) -precipitates. In the present investigation, we studied the load distribution between the different phases of LAE442 as well as the evolution of the lattice strains under tensile and compressive loading in order to gain valuable insight into the deformation behavior of the alloy. In-situ deformation experiments coupled with energy dispersive diffraction by means of high energy synchrotron radiation allow this kind of investigation. High energy synchrotron X-ray stress analyses were carried out on cylindrical specimens that were uniaxially loaded. The diffraction experiments were carried out at the EDDI-beamline at BESSY II, Berlin, using a white beam up to energies of 150 keV. Diffraction data were analyzed according to the well known sin²y - method. As a result of the studies the X-ray elastic constant (XEC) ½ s2{hkl}was evaluated for the individual phases.