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| 題名: | 錳、鋯與鈧對Al-5Mg合?再結晶、成型性及腐蝕性質之影響;Effects of Mn, Zr and Sc on Recrystallization, Formability and Corrosion Behavior of Al–5Mg Alloy in Different Annealing Temperatures |
| 作者: | 邱揚淳;Chiu, Yang-Chun |
| 貢獻者: | 材料科學與工程研究所 |
| 關鍵詞: | 鋁鎂合金;製程退火;沿晶腐蝕;再結晶性;成型性;aluminum-magnesium alloy;process annealing;intergranular corrosion;recrystallization;formability |
| 日期: | 2021-08-25 |
| 上傳時間: | 2021-12-07 11:57:14 (UTC+8) |
| 出版者: | 國立中央大學 |
| 摘要: | Al-5Mg鋁合金之型材(shapes)主要是利用高度冷加工來成型，因此合金型材在存放溫度為40至50℃時就會產生敏化現象(Sensitization)，隨著鎂含量的提高及暴露時間之增長，β-Mg2Al3相會大量析出於晶界上，並導致嚴重之沿晶腐蝕(Intergranular Corrosion)，使其存放條件大幅被限制，故如何提升其抗腐蝕性為Al-5Mg鋁合金之相當重要議題。目前以高溫製程退火(300至450℃)能將Al-5Mg鋁合金再結晶並消除內部儲存能，讓合金形成安定狀態，且減少β-Mg2Al3相析出，進而大幅度增加其抗腐蝕性，然而在再結晶過程中，晶粒非等向成長(Anisotropic grain growth)對後續成型性有不良之影響，故同時提升抗腐蝕性與成型性是Al-5Mg鋁合金相當重要之議題
本研究藉由合金設計及製程退火熱處理，來探討合金元素對Al-5Mg合金在不同製程退火溫度下對合金微結構、成型性與腐蝕性質之影響，以完整呈現此鋁鎂合金之特性。
由於錳、鋯與鈧為鋁合金中影響再結晶之重要合金元素，於本論文中，將不同元素含量(0.1 wt%Mn、0.1 wt%Zr與0.05 wt%Sc)之合金施以不同製程退火溫度等熱處理來探討微量Mn、Sc和Zr對Al-5Mg合金在不同製程退火溫度下對再結晶微結構、機械性質與成型性之影響。爾後，再藉由敏化處理(150℃下100小時)來探討在不同再結晶程度下，其腐蝕性質之變化。
本論文藉由金相、導電度(%IACS)、電子背向散射繞射(EBSD)、電子微探儀(EPMA)、電子顯微鏡(TEM與SEM)等微結構觀察與分析，並配合硬度(HV)、拉伸試驗與多方向拉伸試驗，而獲得以下結論：
再結晶過程中，含Zr、Sc合金之Al3Zr與Al3Sc顆粒在抑制(次)晶界移動的效力上優於含Mn合金之析出顆粒Al6Mn，從而得知含Zr、Sc合金較含Mn合金具有較佳之抑制再結晶能力；在高溫450℃之下，含Sc合金其抑制晶粒成長效果又優於含Zr之合金，結果顯示，Al3Sc顆粒之熱穩定優於Al3Zr；另外在晶粒成長階段，含Zr合金之再結晶晶粒為等向性成長(Isotropic grain growth)、含Mn合金為非等向成長(Anisotropic grain growth)，而含Sc合金無明顯晶粒成長。
另外藉由多方向拉伸試驗(0°、45°、90°)與結晶方位分布函數(ODF)分析合金成型性之優劣，發現其原因與合金晶粒成長方式與成長方位有關，往Weak Cube(001)<120>等向性成長之含Zr合金的成形性最佳，而往Weak Cube(001)<120>非等向成長之含Mn合金次之、無明顯晶粒成長含Sc合金最差。
而從再結晶程度、微結構與NAMLT試驗中可以得到以下結論：合金於再結晶過程中的回復階段，β-Mg2Al3相將析出於次晶界上，其降低了合金沿晶腐蝕的發生，而在再結晶初期下，β-Mg2Al3相將連續析出在晶界上，將導致合金發生明顯沿晶腐蝕現象。而含Sc之合金，由於無明顯晶粒成長階段，造成β-Mg2Al3相連續析出在晶界上而產生沿晶腐蝕，使合金腐蝕性質大幅下降；相較之下，含Mn、Zr合金則有明顯晶粒成長現象，而在晶粒成長後鎂原子有聚集之現象，使β-Mg2Al3相(Mg2Al3)會在晶界上不連續析出，其腐蝕形貌為局部孔蝕而非沿晶腐蝕，進而提升合金之抗腐蝕性質。
;Al-5Mg aluminum alloy shapes are mainly formed by a high ratio of cold working. Sensitization occurs when the alloy shapes are stored at the temperatures of 40 to 50℃. With the increase of magnesium content and exposure time, β-Mg2Al3 phase will precipitate on the grain boundary in a large amount and cause severe intergranular corrosion, which greatly limits its storage conditions. At present, high-temperature annealing (300 to 450℃) is adopted to recrystallize Al-5Mg aluminum alloy and eliminate its internal stored energy so that the alloy can form a stable state. It can also reduce the precipitation of β-Mg2Al3 phase to greatly increase its corrosion resistance. However, During the recrystallization process, anisotropic grain growth has an adverse effect on the subsequent formability. Therefore, how to enhance the corrosion resistance and formability of Al-5Mg aluminum alloy at the same time is a very important issue.
In this study, alloy design and heat treatment are adopted to explore the effects of alloying elements on the microstructure, formability and corrosion properties of Al-5Mg alloys at different annealing temperatures in order to fully present the characteristics of these aluminum-magnesium alloys.
Manganese, zirconium and scandium are important alloying elements that affect recrystallization in aluminum alloys, so in this research, alloys with different element contents (0.1 wt%Mn, 0.1 wt%Zr and 0.05 wt%Sc) are subjected to annealing processes and other heat treatments at different temperatures to explore the effects of trace amounts of Mn, Zr and Sc on the recrystallized microstructure, mechanical properties and formability of Al-5Mg alloys. After that, sensitization treatment (for 100 hours at 150℃) was used to investigate the changes in corrosion properties with different degrees of recrystallization.
In this research, by way of microstructure observations and analyses of the metallography, electrical conductivity (%IACS), electron backscatter diffraction (EBSD), electron microprobe (EPMA), electron microscope (TEM and SEM), hardness test (HV), tensile test and multi-directional tensile test, the following findings were obtained.
During the recrystallization process, the precipitated Al3Zr and Al3Sc particles in the Zr-containing and Sc-containing alloys were more effective in inhibiting (sub)grain boundary migration than the precipitated Al6Mn particles in the Mn-containing alloy. Therefore, it is known that the alloy containing Zr or Sc inhibited recrystallization better than the alloy containing Mn. At a high temperature of 450℃, the Sc-containing alloy was more effective in inhibiting grain growth than the Zr-containing alloy. The results showed that the thermal stability of Al3Sc particles was better than that of Al3Zr particles. In addition, during the recrystallized grain growth stage, the recrystallized grains of the Zr-containing alloy showed isotropic grain growth while the recrystallized grains of the Mn-containing alloy showed anisotropic grain growth. No obvious grain growth occurred in the recrystallized grains of the Sc-containing alloy.
In addition, the multi-directional tensile test (0°, 45°, 90°) and crystal orientation distribution function (ODF) were performed to analyze the formability. It was found that the formability was related to the growth mode and direction of the grains. The formability of the Zr-containing alloy with isotropic grain growth toward Weak Cube(001)<120> was the best. The formability of the Mn-containing alloy with anisotropic grain growth toward Weak Cube (001)<120> was the next best. The formability of the Sc-containing alloy with no obvious grain growth was the worst.
The following conclusions were drawn from the different degrees of recrystallization, microstructure and NAMLT test. During the recovery stage of the recrystallization process, the β-Mg2Al3 phase precipitated on the subgrain boundary, which reduced the occurrence of intergranular corrosion of the alloy. At the initial stage of recrystallization, β-Mg2Al3 phase continuously precipitated on the grain boundary, resulting in the obvious intergranular corrosion. For the Sc-containing alloy, because there was no obvious grain growth stage, the β-Mg2Al3 phase continuously precipitated on the grain boundary and intergranular corrosion occurred, which greatly reduced the corrosion properties of the alloy. In contrast, the alloys containing Mn or Zr had obvious grain growth phenomenon. After the grain growth, magnesium atoms aggregated and consequently the β-Mg2Al3 phase discontinuously precipitated on the grain boundary. Their corrosion morphology showed local pitting corrosion rather than intergranular corrosion. Thus, the corrosion resistance was enhanced. |
| 顯示於類別: | [材料科學與工程研究所 ] 博碩士論文
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