Processing-Controlled Mechanical Properties and Microstructures of Bulk Cryomilled Aluminum-Magnesium Alloys

摘要

We have been successfully realizing bulk nanostructured aluminum alloys via a process of cryomilling, consolidation and extrusion. The resulting extrusions have consistently demonstrated greatly enhanced strength relative to conventional materials while the grain size after processing is generally in the range of 100 to 300 nm. Within the nanostructured matrix we find grains that are on the order of several hundred nm's and often elongated in the extrusion direction. The suggestion that these grains are responsible for increasing the ductility of the materials inspired an effort to engineer ductility via the concept of multiple length scales. We present mechanical property data for cryomilled Al-Mg alloys that were processed under different consolidation and extrusions conditions, as well as materials engineered for higher ductility through the addition of unmilled powder to the cryomilled prior to consolidation. In (he latter case, the presence of 15, 30 and 50 weight percent unmilled powder enhanced the ductility relative to the all-cryomilled samples without sacrificing the strength derived from the grain-size refinement and cryomilling-related dispersoid strengthening in the matrix.