dc.description.abstract | This study purpose uses a different feed rate of rolling reduction, to research and discuss the microstructures and mechanical properties of a series of super light magnesium-lithium alloys. Adding Li raises Mg alloy formability and promotes improving cool and heat deformation ability. Previous researches indicate that Mg-Li alloys lack of strength and work hardening, therefore we wish to increase its strength and work hardening by adding Sc and Be into the alloy, creating two alloys, LAZ1110, LAZ1110+ Be &Sc, respectively.
And we also use different processes to enhance the mechanical properties, such as solid solution treatment and cold work strengthening. Each material is rolled reduction by 30%, 60% and 90%. Experimental rolling reduction feed rate uses 10% and 15% to compare the test data difference. After Mg-Li alloy 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 of a feed rate 15% can obtain a maximum strength of about 281MPa. It’s apparently higher than a maximum about 246MPa of 90% rolling reduction of a feed rate 10%. Follow prior thesis, we can infer if 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 maximum tensile strength.
In microstructures, experimental results show that two alloys change from α+β-phase to a single β-phase after solid solution treatment. After rolling the grains are elongated and α-phase will precipitate with increasing rolling percentage. The two 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 90% 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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