| dc.description.abstract | This research discusses the microstructures and mechanical properties of a series of super light magnesium-lithium alloys. The density of the Mg-Li alloy is approximately 1.46g/cm3. Previous researches indicate that Mg-Li alloys lack of strength, therefore we wish to increase its strength by adding Sc and Be into the alloy, creating four alloys,LAZ1110, LAZ1110+Be, LAZ1110+Sc, LAZ1110+ Be &Sc,respectively.
And we also use different processes to enhance the mechanical properties, such as solid solution treatment and cold work strengthening. On the other hand, we use thermo mechanical treatment to obtain a refined grain size and attain superplasticity. Experimental results indicate that when the Mg-Li alloy is extruded and rolled, the as-extruded material with 90% rolling reduction can obtain a maximum tensile strength about 200Mpa. Another process is extrusion plus solid solution and then cold rolling. Due to the superimposition effect of solid solution strengthening and cold work strengthening, the material after 90% rolling reduction can obtain a maximum strength of 246Mpa. The last process, the material is extruded, solid solution treated and cold rolled before aged. The material aged under room temperature after 20~40hrs will have peakaging with tensile strength of 253Mpa.
In microstructures, experimental results show that all four alloys possess a single β-phase after solid solution treatment. After rolling the grains are elongated and α-phase will precipitate with increasing rolling percentage. The four alloys’ specimens after extrusion, solid solution and cold rolling were annealed at 50、100、150、200、250℃, respectively, for 30min. Their grain size increases with increasing annealing temperature. When annealing temperature reaches 250℃, uniformed static recrystalled grains can be observed, especially in specimens with 30% and 60% rolling reduction whose grain size is less than 10μm which is suitable for superplasticity tests. When Mg-Li alloys are placed under room temperature α-phase will precipitate resulting in a decrease in strength and overaging.
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