Structure And Mechanical Properties Of Bulk Nanocrystalline Aluminium

Bulk nanocrystalline Al are fabricated by cryomilling, compacting, vacuum sintering and extrusion with hard particle addition to improve the strength and hardness of the material. Microstructure of the materials are observed and analyzed by TEM and XRD. Density, microhardness and tensile property of the materials are measured. Experiment results demonstrate that grain size of the aluminum powder is reduced from 55 to 43 nm, and microstrain of the crystalline materials is increased from 0.0272 to 0.0759 % when the cryomilling time is increaseed from 8 to 14 h. Grain sizes of the bulk nanocrystalline Al is reduced from 115 to 71 nm. The relative densities of the bulk nano Al and Al-Al2O3 crystalline materials are more than 99.4 % after hot extrusion. The maximum microhardness of the two kinds material are 1.02 and 1.22 GPa, which are 3.0 and 3.6 times higher than that of coarse-grained Al. The maximum yield and tensile stress of the bulk nano Al reach 165 and 243 MPa which are 7.5 and 3.2 times higher than that of commercial 1050 pure aluminum. The maximum yield and tensile stress of the bulk nano Al-Al2O3 reach 242 and 305 MPa which have a 47 and 20 % stress of increase compared with the bulk nano Al under the same processing condition. When the grain size is below 223 nm, the relationship between yield stress and grain size of the bulk nano Al material is expressed asσ'= 71.8 + 1.8D?1/2. The maximum elastic mould of the bulk nano Al is 71.8 GPa which is 4 % improvement on the elastic mould of the coarse-grained Al. Under the same processing condition, the maximum elastic mould of the bulk Al-Al2O3 is 76.8 GPa which is 7 % improvement on the elastic mould of the bulk nano Al. The minimum elongations of the bulk nano Al and Al-Al2O3 crystalline materials are 6.4 and 5.8 % which account for 16 and 15 % of he coarse-grained Al. The relative densities, microhardness, strength and elastic mould of the two kinds of material are increased with reducing of grain size, but the elongations are decreased.