| 摘要: | 本研究目的探討超輕鎂鋰合金之顯微組織與機械性質。鎂鋰合金其密度約為1.46g/cm3，又以往之研究結果顯示、鎂鋰合金的強度不是很突出，為了提高Mg-Li合金的強度，添加Sc和Be元素進入Mg-Li合金中。形成LAZ1110、LAZ1110+Be、LAZ1110+Sc及LAZ1110+Be&Sc四種合金。 再利用不同的製程來提升機械性質，如固溶強化與冷加工強化；另一方面配合熱機處理，嘗試獲得微細之晶粒的鎂鋰合金材料，進而達到超塑性。由實驗可以發現到，當鎂鋰合金經過擠製+軋延後，擠製材在軋延90%後其最高強度可達200MPa左右；另一製程經擠製+固溶+軋延後，因為固溶強化與加工強化效果疊加，使得在軋延90%後最高強度可達246Mpa左右，最後，擠製+固溶+軋延時效後，材料於室溫時效下20~40hrs時會有尖峰時效產生，最大抗拉強度約253MPa。 顯微組織方面，由實驗結果可以發現到，四種合金經過固溶處理後皆為單一β相，經過軋延後晶粒被拉長呈現長條狀的晶粒，而隨著軋延率的上升α相也隨著析出。四種合金經過擠製+固溶+軋延後之試片，施以50、100、150、200、250℃×30mins退火處理後，其晶粒隨著溫度上升而增大，但是溫度達250℃時可以觀察到均勻的靜態再結晶之晶粒，尤其是軋延率30%、60%之試片，其晶粒均小於10μm，適合用於超塑性之試驗。當鎂鋰合金置於室溫下，α相的析出會造成強度的下降而有過時效的效果。 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. |
