Research On Stress Relaxation And Creep Properties Of The Ultra-Fine Grained Aluminum-Magnesium Alloy

The tensile properties of Al-6Mg and Al-3.7Mg-0.2Zr alloys deformed via equal channel angular pressing(ECAP) dies with 120°and 90°respectively were estimated at 473K.The tensile tests were carried out for the Al-6Mg alloys deformed via ECAP under conditions that the temperature range is from 298K to 373K and the initial strain rate varies from 4×10^-5/s to 4×10^-3/s by Russian multi-function loading testing machine. The regulation of the stress relaxation and the creep behaviors were estimated with the initial load of 345MPa at the strain rate of 2.4mm/s. The microstructures of the tested alloys before and after the ECAP deformations and the creeped were investigated by transmission electron microscopy and optic microscope. Models describing the stress relaxation and the creep behaviors of the Al-6Mg alloys under the experimental conditions were proposed. For the stress relaxation model and steady creep behaviors model of the ECAPed Al-6Mg alloys areσ=A_0A1e^{- r-B₀/B₁}+A₂e^{- r-B₀/B₂}+A₃e^{- r-B₀/B₃} andε=A-B/T, respectively. They therefore provide a guidance to predict and evaluate the stress relaxation and creep behaviors of the Al-6Mg alloys at low temperatures.Experimental results show that the extrusion process have obviously strengthening effect for the Al-6Mg alloy with the increase of the passes of the ECAP,the microstructure of the Al-6Mg alloys was changed from the initial coarse equiaxed grains to the ultra-fine grains and subgrains,resulting a significant increase in strength, but a decrease in the elongation.Thus, the microstructures and the mechanical properties of the Al-6Mg alloys were improved by the passes of the ECAP. It was also shown that the mechanical properties of the Al-6Mg alloys are strongly dependent on the deformation temperature and the strain rate. The strength of the deformed Al-6Mg alloys by the ECAP was dramatically decreased and the elongation was significantly increased by either decreasing the strain rate or increasing the temperature. During the process of the creeps from 298K to 363K temperatures, the microstructures of the Al-6Mg alloys were not changed from the ultra-fine grains. However, the dislocation configurations were changed from originally tangled shape to regular dislocation array with the increase in creep time. The morphological character of sharp and straight in the grain and subgrain boundaries faded away, come into view of soften and arch features, the properties of anti-creep behaviors gradually decrease with the grain and subgrain merged in the part area.