- 學位論文
鎂的添加對55.0wt.%鋁鋅微組織及各項性質之研究
Investigation into the effects of Mg addition in the 55.0wt.% Al-Zn alloy on the microstructure, thermal properties and corrosion resistance
摘要
為了解添加鎂對55.0wt.%鋁鋅(Galvalume)的影響，本研究共設計四組鋁鎂鋅合金鋅-55.0wt.%鋁-X wt.%鎂-1.6wt.%矽(X=0, 1.0, 2.0, 3.0)，並在合金鑄件的煉製過程中利用預熱的銅合金模具，以達到接近實際產線的冷卻速率。合金煉製後再分別針對其顯微組織、熱物性質、機械性質及耐蝕性質等，進行各項實驗結果分析與綜合評估，以期得到較佳的鎂添加比例。 實驗結果顯示，在微組織觀察中得知55.0wt.%鋁鋅其結構主要分為富鋁基地相與晶界的鋁鋅二元共晶及富鋅相。當55.0wt.%鋁鋅合金鑄件添加1.0wt.%鎂後，可在晶界上觀察到MgZn2相的存在；而添加2.0wt.%鎂後晶界上則會開始出現Mg2Si相，兩者皆隨著鎂的添加量上升有增加的趨勢，對其機械、物理性質及耐蝕性皆有一定的影響。在熱物性質的部分，透過高溫示差掃描分析儀(Differential Scanning Calorimeter, DSC)實際量測到的相變化溫度點，與Thermo-Calc模擬相圖進行比對，可以驗證顯微組織的觀察結果，並發現隨著鎂的添加量逐漸增加將可使液化溫度出現下降的趨勢。而在機械性質的部分，利用微小維氏硬度機(Micro-Vickers Hardness Tester)測量硬度值的變化，得到隨著鎂的添加量逐漸增加硬度值有上升的趨勢。 在耐蝕性質的部分，從電化學結果得知添加1.0wt.%鎂有最低的腐蝕速率，以及在添加2.0wt.%鎂有較寬廣的鈍化區間；而鹽霧測試的結果則顯示鎂的添加量在介於1.0wt.%和2.0wt.%之間時，整體上有較佳的耐蝕表現。
並列摘要
To investigate the effects of magnesium (Mg) additions in the 55.0 wt.% Al-Zn alloy on the microstructure evolution and other properties, four aluminum-magnesium-zinc alloys (55.0 wt.% Al-X wt.% Mg-1.6 wt.% Si-Zn and X=0, 1.0, 2.0, 3.0) were designed and produced in this study. To obtain a cooling rate during the solidification of the experimental work closing to that during the real manufacturing process, a preheated copper alloy molds was used for the experimental casting processes. After then, the microstructure, thermal properties, mechanical properties and corrosion resistance were investigated and comprehensive evaluated to obtain the better alloy design. Experimental results are shown, the main phases of the 55.0 wt.% Al-Zn alloy include aluminum-rich matrix phase and, the aluminum-zinc binary eutectic and zinc-rich phases locating in the grain boundary. MgZn2 phase and Mg2Si phase in the grain boundary were observed, when the alloys added 1.0 wt.% and 2.0 wt.% of magnesium, respectively, which may substantially affect their properties and corrosion resistance. For the thermal properties of the alloys, through the Differential Scanning Calorimetry tests and Thermo-Calc phase diagrams simulation, it was found that the liquation temperature gradually decreases with the increased amount of Mg. Regarding to the mechanical properties, the Vickers hardness values increases with the increased magnesium additions Finally, from the electrochemical test, it was found that the addition of 1.0 wt.% of Mg has the lowest corrosion rate and the addition of 2.0 wt.% of Mg has a wider passivation ranges. And the salt spray test results are shown, 1.0 wt.% and 2.0 wt.% of Mg additions had better corrosion resistance.