Nanocrystalline 6061 Al Powder Fabricated by Cryogenic Milling and Consolidated via High Frequency Induction Heat Sintering

Nanocrystalline 6061 Al alloy was synthesized by cryogenic milling (cryomilling). Both transmission electron microscopy and X-ray diffraction were used to monitor the change in grain size as a function of milling time. The results of both techniques demonstrated a close agreement with respect to two observations: (a) during cryomilling, the grain size of 6061 Al decreased with milling time, and (b) after 15 h of milling, the grain size approached a minimum value of about 22 nm. Despite this agreement, there was a discrepancy: for grain sizes > 40 nm, the grain size measured by transmission electron microscopy was appreciably larger than that inferred from X-ray diffraction. It was shown that powders consolidated via high frequency induction heat sintering (HFIHS) at 500 and 550°C maintained close to nanoscale grain sized microstructure in addition to high compact density in bulk samples. This was manifested by high strength values as compared to microscale grain samples.