AZ31鎂合金滾軋板材經ECAE多重降溫擠型10道次，晶粒細化至0.46 μm，basal面從原始滾軋板材Y面旋轉至與Z面平行，ECAE後再退火處理得到平均晶粒尺寸為0.62至3.22 μm的試片，退火前後的織構並未明顯產生變化。
極細晶鎂合金在室溫至125℃以3*10-5至6*10-2 s-1的應變率進行拉伸試驗，結果顯示晶粒細化後在室溫的降伏強度獲得很大的改善，在應變率3*10-3 s-1的拉伸降伏強度高達394 MPa。隨著溫度的升高，極細晶鎂合金試片的應變率靈敏度從室溫的0.024增至125℃的0.321。與拉伸強度及晶粒尺寸有關的Hall-Petch equation, σ=σ0 + kd-1/2中的斜率k值隨著溫度的升高及應變率的降低而下降。在應變率3*10-5 s-1，在75℃及100℃的時k值皆呈現負值。在室溫不同方向壓縮變形，應變集中的shear bands形成於X、Y及X45Z方向的試片。不同方向壓縮試片變形機構的不同，造成Hall-Petch k值的差異。當晶粒尺寸小到0.46 μm時，雙晶變形仍然出現，拉伸/壓縮降伏非對稱性仍然存在。

Ultrafine-grained(UFG) AZ31 Mg alloy was obtained by equal-channel angular extrusion(ECAE) and subsequent annealing at elevated temperatures. The basal texture component for ECAEed material is located on the Z plane of the ECAEed billets. Tensile tests were performed at temperatures between room temperature and 125℃, and strain rates used ranging from 3*10-5 to 6*10-2 s-1. The experimental results showed that a high tensile yield stress of 394 MPa was obtained at room temperature under a strain rate of 3*10-3 s-1. Strengths of UFG AZ31 specimens were greatly improved due to grain refinement. It was found that strain rate sensitivity of UFG AZ31 alloy increased significantly from 0.024 to 0.321 with increasing temperature. The constant k of Hall-Petch equation, σ=σ0 +kd-1/2, decreased with increasing temperature, and decreasing strain rate. Negative k values were ontained at 75℃ and 100℃ under a strain rate 3*10-5 s-1.

When compressed along X, Y and X45Z billet orientations, strain localization within shear bands was found in UFG AZ31 specimens. Shear bands are formed inclined near 45 to the compression axis. The smaller the grain size, the thinner the shear band. Different Hall-Petch constant k were found in specimens deformed along different orientations, which is caused by different deformation mechanisms. The formation of tension twins is the primary deformation mechanism for compressed X and Y samples, and basal slip is responsible for the deformation of X45Z sample. tension twins were found in 0.46 μm grain size specimens.

目錄 頁次
表目錄………………………………………………………………………………..IV
圖目錄………………………………………………………………………………...V
壹 前言………………………………………………………………………………..1
貳 文獻回顧…………………………………………………………………………..2
2-1 等徑轉角擠型(ECAE)……………………………………………………......2
2-1-1 影響非鎂合金ECAE變形的參數.……………………………….….2
2-1-2 非鎂合金ECAE晶粒細化的原理..………………………………. ..17
2-1-3 影響鎂合金ECAE變形的參數…………………………………….18
2-1-4 鎂合金ECAE晶粒細化的原理..……………………………………25
2-1-5 ECAE擠製後的texture變化………………………………………...27
2-2 ECAE變形後的機械性質………………………………………………..….30
2-2-1 晶粒細化對機械性質的影響……………………………………….30
2-2-2 Texture對機械性質的影響………………………………………….31
2-3 極細晶(Ultrafine-grained, UFG)材料的變形行為…………………………33
2-4 鎂合金的塑性變形與機械性質…………………………………………….40
2-4-1 鎂合金的塑性變形行為…………………………………………….40
2-4-2 鎂合金的機械性質………………………………………………….43
2-4-2-1 晶粒大小的影響…………………………………………..43
2-4-2-2 應變率的影響……………………………………………..45
2-4-2-3 溫度的影響………………………………………………..46
2-4-2-4 受力方向與texture的影響……………………………….48
參 研究目的………………........................................................................................53
肆 實驗方法…………………………………………………………………………54
4-1 材料及ECAE設備………………………………………………………….54
4-2 ECAE的試棒製作…………………………………………………………..54
4-3 ECAE退火試片的製備…………………………………………………...55
4-4 OM及SEM的試片製備………………………………………………….55
4-5 TEM的試片製備……………………………………………………….….56
4-6 SEM及TEM的晶粒尺寸量測………………..………………………….57
4-7 硬度試驗試片的製備…………..……………………………….…………57
4-8 Txture的試片製備...…………………………………………………….…57
4-9 拉伸試片的製備…………………………………………………………...58
4-10 壓縮試片的製備…….……………………...……………………………...59
伍 結果………………………………………………………………………………61
5-1 ECAE晶粒細化結果………………………………………………………...61
5-1-1 ECAE 變形理論結果………………………………………………….61
5-1-2 ECAE多重降溫擠製晶粒細化結果………………………………….61
5-1-3 ECAE擠製後之織構………………………………..………………...62
5-1-4不同晶粒尺寸的退火處理結果………………………………………62
5-2 機械性質測試結果………………………………………………………….62
5-2-1 硬度試驗結果……………………………………………………….62
5-2-2 拉伸變形行為的觀察…………………………………………….…63
5-2-2-1 室溫拉伸試驗結果………………………………………..63
5-2-2-2 高溫拉伸試驗結果………………………………………..63
5-2-2-3 不同擠製道次的拉伸試驗結果…………………..............65
5-2-2-4 應變速率靈敏度的量測…………………………………..66
5-2-2-5 拉伸變形後的微觀組織…………………………………..66
5-2-2-6 溫度及應變率對拉伸變形的影響………………………..66
5-2-3室溫壓縮變形行為的觀察…………………………………………67
5-2-3-1 不同方向試片的壓縮……………………………………67
5-2-3-2 室溫壓縮變形之後的表面組織…………………………69
5-2-3-3在室溫壓縮變形後texture的變化………………………70
5-2-3-4 室溫壓縮變形後的微觀組織……………………………70
陸 討論………………………………………………………………………………71
6-1 鎂合金ECAE晶粒細化機制……………………………………………….71
6-2 多重降溫擠製對ECAE晶粒細化的影響………………………………….72
6-3 ECAE對鎂合金texture的影響……………………………………………..73
6-4 極細晶AZ31鎂合金的變形行為及機制…………………………………..73
6-5 晶粒大小的影響…………………………………………………………….77
6-5-1 晶粒大小對降伏強度的影響……………………………………….77
6-5-2 晶粒大小對應變硬化行為的影響………………………………….80
6-6 溫度的影響………………………………………………………………….81
6-7 應變率的影響……………………………………………………………….82
柒 結論………………………………………………………………………………84
捌 參考文獻…………………………………………………………………………85

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