Y. Xun, F. Mohamed, University of California, Irvine, Irvine, CA
Tensile tests were performed on a cryomilled Al-6.5%Mg with an average grain size of 300 nm at temperatures of 473, 573 and 673 K and strain rates of 10-2, 10-3 and 10-4 s-1. The microstructures associated with deformation were characterized by means of transmission electron microscopy (TEM). Experimental data show that ductility increases with increasing strain rate and decreasing temperatures. A considerable strain hardening behavior was observed in the sample tested at 473 K and 10-2 s-1. Three types of deformation microstructures were identified: fine equaxid, coarse equiaxid and elongated band-like structures. The dislocation density was found to decrease with deformation. Consideration of these observations leads to the conclusion that grain boundary sliding rather than conventional dislocation slip serves as the major deformation mechanism. The observed mechanical behavior can be explained in terms of the effects of the complex microstructures developed and the accommodation process for grain boundary sliding.
Summary: Tensile tests were performed on a cryomilled Al-6.5%Mg with an average grain size of 300 nm at temperatures of 473, 573 and 673 K and strain rates of 10-2, 10-3 and 10-4 s-1. The microstructures associated with deformation were characterized by means of transmission electron microscopy (TEM). Experimental data show that ductility increases with increasing strain rate and decreasing temperatures. A considerable strain hardening behavior was observed in the sample tested at 473 K and 10-2 s-1. Three types of deformation microstructures were identified: fine equaxid, coarse equiaxid and elongated band-like structures. The dislocation density was found to decrease with deformation. Consideration of these observations leads to the conclusion that grain boundary sliding rather than conventional dislocation slip serves as the major deformation mechanism. The observed mechanical behavior can be explained in terms of the effects of the complex microstructures developed and the accommodation process for grain boundary sliding.
