| 摘要: | 本研究目的為探討新型超輕鎂合金之顯微組織與機械性質。選用具有低密度及室溫良好成形性之Mg-Li系列合金為研究對象，添加微量Be、Sc元素，形成LAZ1110、LAZ1110+Sc、LAZ1110+Be及LAZ1110+Be&Sc四種合金，但因此系列合金缺乏足夠的機械強度與加工硬化效能，故我們利用不同的製程如擠製+冷軋、擠製+固溶、擠製+固溶+時效及擠製+固溶+冷軋，一方面藉由固溶強化與冷加工強化之效果來提昇材料機械強度與加工硬化能力；另一方面配合熱機處理製程技術，嘗試獲得微細晶粒的鎂鋰合金板材，進而達到超塑性。 機械性質方面，實驗結果發現在擠製+冷軋製程中，擠製材經過90%軋延率冷軋延後其抗拉強度皆可達到200MPa左右；而另一製程經擠製+固溶+冷軋，擠製材先經350℃×1hr固溶處理後立即水淬，再經90%軋延率冷軋延，因固溶及加工強化雙重效果下致使抗拉強度提昇至240MPa上下；最後，在擠製+固溶+時效製程中，材料於室溫時效下20 ~ 40hrs間會有peak值出現，最大抗拉強度約250MPa。 顯微組織方面，實驗結果發現四種材料一致性地在擠製+固溶+冷軋製程後，施於250℃×30mins退火後便可觀察到軋延率30%與60%軋延下的金相組織呈現細小且等軸晶粒其晶粒大小均<10μm，適合超塑性拉伸實驗之試樣。 This research probes into the microstructure and mechanical properties on the new ultra light magnesium alloy. Choose the LAZ1110 magnesium alloy (Mg-11%Li-1%Al-0.5%Zn) which have low density and high formability at room temperature research object. Adding Be and Sc elements into Mg-Li alloys. Four Mg-Li alloys; a bare one (LAZ1110), the second with Sc, the third with Be and the fourth with both Sc and Be, but Mg-Li series alloys normally have low strength and poor precipitation hardening effect. Therefore we use the different processes such as extruded/cold rolled, extruded/solid solution treatment, extruded/solid solution treatment/natural aging, and extruded/solid solution treatment /cold rolled. On the one hand, in order to enhance their strengths and work hardening ability by solid solution treatment and cold work. On the other hand, in order to obtain fine grain size on Mg-Li series alloys, making use of plastic deformation such as hot extrusion, cold rolling ect plus TMT (thermo mechanical treatment) technique. On mechanical properties, show by the experimental result, for the process of extruded/cold rolled, the ultimate tensile strength achieve about 200MPa with 90% rolling. For other process of extruded/solid solution treatment /cold rolled, the plates were solution treated at 350oC for one hour and quenched, then for rolling reduction of 90%, the ultimate tensile strength achieve about 240MPa because solid solution treatment and work hardening effect. Finally, for the process of extruded /solid solution/natural aging, and at room temperature aging, the peak value appears within 20~40 hours, the ultimate tensile strength approximately 250MPa. On microstructure, show by the experimental result, all the four alloys uniformly found after the process of extruded/solid solution treatment /cold rolled that 30% and 60% rolling reduction then followed by 250oCx30mins annealing, a fine grain structure was obtain, the grain size of the structure is smaller than 10μm. |
