Particle Hardening in Creep-Resistant Mg-Alloy MRI 230D Probed by Nanoindenting Atomic Force Microscopy

Two different Mg alloys, AZ91 and MRI 230D, have been investigated with the objective to understand the differences in high-temperature deformation behavior. AZ91 is known for its rather poor creep resistance; in contrast to this, MRI 230D is known to have a rather high resistance against plastic deformation at elevated temperatures. The microstructure and mechanical properties of as-cast and crept specimens of two Mg alloys (AZ91 and MRI 230D) were characterized by nanoindenting atomic force microscopy (NI-AFM). In the cell interior, a significant higher hardness was found for MRI 230D in comparison to AZ91. Precipitates with an average size of about 50 nm found in the cell interior of MRI 230D after creep deformation are discussed as the major hardening component. Manuscript submitted January 29, 2008.