Accelerated Formation of an Ultrafine-Grained Microstructure in Closed-Cell Aluminum Foam after Extrusion and Differential Speed Rolling

Abstract

Plastic deformation by extrusion and high-ratio differential speed rolling on closed-cell aluminum foams resulted in the formation of ultrafine grains in the densified matrix. The microstructure had an average grain size of 1.30 μm and a fraction of high angle boundaries of 0.7. Under the same processing condition, only dynamic recovery occurred in the bulk aluminum. During deformation of the foam, continuous dynamic recrystallization accelerated at the cell walls due to the occurrence of a high degree of severe plastic deformation there. The bonded interfaces created by pore closure also provided a number of sites of high angle grain boundaries, thereby contributing to the grain refinement.