超輕鎂鋰合金經每道次高壓延進給率後之顯微組織與機械性質研究

Microstructures and Mechanical Properties of LAZ1110 Mg-Li Alloy after A Feed Rate of Heavy Rolling Reduction

高嘉宏(Chia-hung Kao)

指導教授 ： 李雄

國立中央大學/工學院/機械工程研究所碩士在職專班/碩士(2011年)

摘要

本研究目的為藉由不同壓延進給率方式，探討超輕鎂鋰合金之顯微組織的變化與機械性質的改變。鋰的加入大大提升了鎂合金的可塑性，使鎂合金具有良好的冷、熱的塑性變形能力，又以往之研究結果顯示，鎂鋰合金的機械強度與加工硬化效能不是很突出，為了提高Mg-Li合金的機械強度與加工硬化效能，添加Sc和Be元素進入Mg-Li合金中，形成LAZ1110及LAZ1110+Be&Sc兩種合金進行研究探討。
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；將材料分別進行壓延30%、60%、90%，由實驗的壓延進給率分別以10%與15%比較可以發現到，當鎂鋰合金製程經過擠製+固溶+壓延後，因為固溶強化與冷加工強化效果疊加，使得在當進給率15%的壓延90%後的最高強度可達281MPa左右，明顯高於當進給率10%的壓延90%後的最高強度約246 MPa，依先前文獻推知如經另一製程擠製+固溶+壓延時效後，鎂鋰合金材料於室溫時效下20~40hrs時會有尖峰時效產生，可產生最大抗拉強度。
顯微組織方面，由實驗結果可以發現到，兩種合金經過固溶處理後由α+β的雙相結構固溶為單一β相，經過壓延後晶粒被拉長呈現長條狀的晶粒，而隨著壓延率的上升α相也隨著被析出。兩種合金經過擠製+固溶+壓延後之試片，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，尤其是壓延率90%之試片，其晶粒均小於10μm，適合用於超塑性之試驗。當壓延過後之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。

關鍵字

壓延 ； 固溶處理 ； 鎂鋰合金 ； 晶粒細化

並列摘要

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.

並列關鍵字

Grain refining ； Magnesium-Lithium alloy ； Rolling ； Solution treatment

參考文獻

14.郭子強, “熱處理對AZ91D鎂合金顯微組織與電化學性質影響之研究”, 國立成功大學, 碩士論文, 民國93年。

2.H. Takuda, T. Yoshii and N. Hatta “Finite-element analysis of the formability of a magnesium-based alloy AZ31 Sheet”, Journal of Materials Processing Technology 89-90(1999) 135-140.

3.H. Takuda, H. Fujimoto and N. Hatta “Modelling on flow stress of Mg-Al-Zn alloys at elevated temperatures”, Journal of Materials Processing Technology 80-81 (1998) 513-516.

4.I.J. Polmear, Mater. Sci. Technol. 10(1994) 1-16.

7.J.Y. Wang, “Mechanical Properties of Room Temperature Rolled MgLiAlZn Alloy”, Journal of Alloys and Compounds, Vol.485, p.241-244, (2009).