Load Partitioning Between Mg17Al12 Precipitates and Mg Phase in the AZ91 Alloy Using In-Situ Synchrotron Radiation Diffraction Experiments

Abstract

Load partitioning between Mg17Al12 precipitates and the magnesium matrix was examined from room temperature to 200 °C using in-situ synchrotron radiation diffraction during uniaxial compressive tests of AZ91 alloy. Precipitation of the Mg17Al12 phase during aging increases the yield stress of the alloy compared to the solutionized state. In addition to the increase in critical resolved shear stress for the activation of the deformation system, the magnesium matrix transfers some of its internal load to the harder Mg17Al12 intermetallic phase. Load transfer is carried out by the accumulation of dislocations at the Mg-Mg17Al12 interface. The increase in the local stress induces a widening of diffraction peaks of the Mg17Al12 phase. At 200 °C, dislocations can easily shear through or climb around Mg17Al12 precipitates reducing dramatically their reinforcing capacity and, therefore, the magnesium matrix must bear a higher fraction of the applied load.