AZ80+3%Li鎂合金時效處理之研究

A Study of Aging Treatment on AZ80+3%Li Magnesium Alloy

林泓霆(Hung-Ting Lin)

指導教授 ： 林新智

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.10290

摘要

近年來全球在輕量化和符合環保需求的潮流之下，鎂合金的重要性與日俱增。其具有高比強度、低密度、比彈性係數佳等優點，再加上礦藏量豐富、再回收性佳，可取代車輛之部分構件以節省能源耗損。另一方面，鎂合金擁有良好的制震能、優異的散熱性及電磁遮蔽性(EMI)，已成為3C產業中最具潛力的材料。
AZ系列鎂合金主要是在鎂中添加鋁和鋅，是目前商業化最成功的鎂合金。當鋁元素含量大於6wt.%時，會形成第二相Mg17Al12。此β相為介金屬化合物，可以達到析出強化的效果，並且提升鎂合金的抗腐蝕性；添加微量鋅則可以對鎂合金達到固溶強化的效果，增加抗潛變的能力，並且降低合金中的雜質含量。然而，AZ系列鎂合金為六方最密堆積結構(HCP)，在常溫加工時，其塑性變形幾乎僅為底面滑移所貢獻。也因為如此，鎂合金一直存在著成形性不佳、延展性不足等問題。鋰為所有元素中密度最低的金屬，僅有0.534 g/cm3。於鎂合金中添加鋰能有 效改善成形性不佳的問題，並且再更進一步降低鎂合金的密度。
本實驗主要研究AZ80+3wt%Li鎂合金，針對其擠製材之基本性質進行分析，並將此AZ80+3wt%Li鎂合金進行熱處理(T5、T6)，探討其析出強化行為和機械性質。實驗結果顯示，此合金的密度僅有1.71g/cm3。在室溫下，無法固溶於母材中的鋰元素傾向和鋁結合形成AlLi相，這也使得AZ80+3wt%Li鎂合金擠製材相對於AZ80有較佳的延展性。同時，AZ80+3wt%Li鎂合金擠製材於110℃、170℃和230℃進行時效處理，皆呈現明顯的析出強化，於110℃時效16小時可以達到最高強度356MPa，硬度也可以達到Hv88.2，此時的析出相為β相Mg17Al12加上AlLi相；另外，AZ80+3wt%Li鎂合金經450℃持溫24小時固溶處理之後，於110℃、170℃和230℃時效處理，亦呈現明顯的析出強化，於110℃時效32小時可以達到最高強度373MPa，硬度也可以達到Hv115.5，此時的析出相則為AlLi相。然而， AlLi於水溶液中相當不穩定，會水解成鋁元素並於水溶液中釋放鋰離子。再加上鋰的活性大，添加3wt%鋰於鎂合金中會大幅降低鎂合金的抗腐蝕能力。

關鍵字

鎂鋁合金 ； 時效處理 ； 機械性質 ； AlLi相

並列摘要

Magnesium alloys are considered as potential candidates for numerous applications, especially in transportation vehicles or lightweight sectors for 3C products owing to their excellent properties, such as low density, high specific strength, high damping capacity and high recycle ability. The AZ series is mainly based on the Mg-Al alloy system and leads most of the magnesium alloys. If the Al addition in these AZ-series magnesium alloys exceeds 6 mass%, the β-Mg17Al12 inter-metallic compounds will precipitate within the matrix and the mechanical strength increases. Furthermore, adding slight Zn into Mg alloys is to enhance their corrosion resistance. These Zn atoms may also have the effect of solid-solution strengthening. However, it is commonly recognized that magnesium possesses poor formability because of its hexagonal close-packed structure. Adding Lithium with extremely low density 0.534 g/cm3 can improve this shortcoming and further reduce weight.
In the present study, by 3mass% addition of Lithium on AZ80 Mg alloy, we study mechanical properties of as-extruded magnesium alloy. Furthermore, to more understand this AZ80+3mass% Mg alloy, the effects of heat treatments (T5 and T6) on its precipitation behavior and mechanical properties will be systematically investigated. Experimental results show that adding 3mass% Li to AZ80 alloy can obviously increase the ductility. Meanwhile, as-extruded AZ80+3%Li specimens will produce the Mg17Al12+AlLi precipitates after aging from 110℃ to 230℃. The 110℃ aged specimen has a maximum tensile strength of 356 MPa with corresponding aging time of 16 hours. The 450℃ solution-treated specimens will produce the AlLi precipitates after aging from 110℃ to 230℃. The 110℃ aged specimen has a maximum tensile strength of 373 MPa with corresponding aging time of 32 hours. However, the addition of 3mass% Lithium on AZ80 Magnesium alloy will reduce the corrosion resistance due to the highly activity of Lithium and hydrolitic reaction of AlLi precipitate.

並列關鍵字

magnesium alloys ； aging treatment ； mechanical properties ； AlLi phase

參考文獻

47.蔡承洋，利用電解還原沉積擴散法備製單一bcc結構之Mg-12Li-XAl-Zn合金(X=3、9)及其應用於鎂電池陽極材料的電化學表現之研究，國立中興大學材料工程學研究所碩士論文(2007)

32.鮮祺振，腐蝕控制，（1998）15。

3.P. Zhang and J. Lindemann, Scripta Materialia, Influence of shot peening on high cycle fatigue properties of the high-strength wrought magnesium alloy AZ80, 52 (2005) 485.

4.P. Zhang and J. Lindemann, Scripta Materialia, Effect of roller burnishing on the high cycle fatigue performance of the high-strength wrought magnesium alloy AZ80, 52 (2005) 1011.

5.F. Andreatta, I. Apachitei, A.A. Kodentsov, J. Dzwonczyk, J. Duszczyk, Electrochimica Acta,Volta potential of second phase particles in extruded AZ80 magnesium alloy, 51 (2006) 3551.