Fabrication And Synthesization Of Bulk Ultrafine-Grained/Nanostructured Light Metals

Nanostructured metallic materials attract great attention from scientific research field due to their peculiar microstructures and physical, mechanical and chemical properties and the great potential for practical applications. In this paper, nanostructured Mg-5w%Al-10.3w%Ti alloy has been fabricated by mechanical alloying and ultrafme-grained bulk pure Al and Al-3%Cu alloy by equal channel angular pressing(ECAP).Nanostructured Mg-5w%Al-10.3w%Ti alloy was prepared by mechanical alloying with the powder mixture of Mg. Al, Ti and process control agent of polyethylene-glycol (H(OCH2CH2)nOH). Compared to conventional powder metallurgy, the mechanical property of the sample synthesized by mechanical alloying shows peculiar strain-softening. TEM analysis shows that the average grain size of the alloy is 20-30nm. Besides, several grains about 90nm and many nanotubes about 3~7nm in diameter are observed.ECAP experiments were conducted on pure Al and Al-3%Cu alloy. The microstructural evolution during ECAP and the influence factors, mechanichal property and the stability of the microstructure of pure Al and Al-3%Cu were investigated. The pure Al was refined from 1.0mm to 0.48μm by ECAP. The refinement saturated after EGA Pressing for 8 passes, corresponding to a maximum hardness value. It was found that such a refined microstructure is stable even after annealing at 150℃ for 1 h. The conventional compression test showed that the as-ECA Pressed sample exhibits a much higher yield strength and a higher strain hardening rate than the unECA Pressed sample. Decreasingtemperature of EGA pressing in pure Al promotes the refinement. Equiaxed grains with high angle grain boundaries are obtained just for 4 passes by EGA Pressing at the lower temperature, in contrast to 8 passes at room temperature. Al-3%Cu alloys as-solid-solutioned and as-aged are subjected to EGA Pressing. The results of TEM analysis and hardness test showed that quantities of coherent particles precipitated in the single-phase solid solution after ECAP for 6 passes, however, its refinement effect is not as significant as that of two-phase alloy after equal passes, in which a large number of incoherent precipitates promote the refinement of ECAP and the strain hardening rate.