本研究採用了AZ91D鑄造用鎂合金來進行鑄鍛的實驗。研究中設計5 mm、10 mm及15 mm三種厚度的鑄件進行鍛造，以求得不同預成型厚度的試片需要多少壓縮率可以完全消除內部的孔洞，以及不同厚度試片所能承受的最大壓縮率為多少。並了解在不同的壓縮率下試片抗拉強度及微組織的變化。

　　由密度量測及拉伸試驗的結果得知，厚度15 mm試片在壓縮率41%時，孔隙率介於1.6 % ~ 0.77 % 之間，已消除大部份的孔洞趨近於理論密度，並且有較佳的抗拉強度163MPa，而所能承受的最大壓縮率在41~51%之間。10 mm厚的試片在壓縮率36%時，孔隙率介於0.61% ~ 0.71%之間，已消除大部份的孔洞趨近於理論密度，而壓縮率到達47%時有較佳的抗拉強度222MPa，而所能承受的最大壓縮率在47%~58%之間。5 mm厚的試片在壓縮率36%時，孔隙率介於0.61% ~ 0.77%之間，已消除大部份的孔洞趨近於理論密度，而在壓縮率48%時有較佳的抗拉強度213MPa，所能承受的最大壓縮率在48%~56%之間。

　　由金相實驗的結果得知，鎂合金AZ91D厚度為10 mm試片在鑄造態時，共晶相(Al12Mg17)呈連續性的在晶粒析出，影響材料的機械強度。在進行拉伸試驗後，由拉伸破斷試片表面得知鎂合金AZ91D在室溫的破壞模式為沿晶破壞。當壓縮率增加的同時(大約在壓縮率50%時)，破壞的模式由完全的沿晶破壞轉變為部份的沿晶破壞及部份的穿晶破壞，進而提升了試片的抗拉強度。接著由拉伸試片破斷面的表面形態可觀察到，鎂合金AZ91D厚度為10 mm試片在鑄造態時，破斷的模式為脆性破壞。而當壓縮率增加到50 %的同時，破斷面的表面形態並無太大的改變仍屬於脆性的破壞模式。

　　In this study, castings with stepwise cross section are die cast with AZ91D magnesium alloy. The stepwise cross section has three different thicknesses, which are 15 mm, 10 mm and 5 mm, respectively. The aim of this study is to evaluate how high compression ratio is required to eliminate the porosities inside the preformed castings with various thicknesses and the maximum compression ratios that can be tolerated before these preformed castings fail. Furthermore, the ultimate tensile strength and microstructures of samples of three thicknesses with different compression ratios will be demonstrated.

　　The experimental results of density measurement and tensile test reveal that for AZ91D magnesium alloy, it requires a compression ratio of 41% to eliminate most porosities (porosity content 0.77%~1.6%) in the casting section 15 mm thickness and a maximum compression ratio range of 41%~51% can be tolerated. Besides, it has a better tensile strength of 163 MPa. For the casting section of 10 mm in thickness, it requires 36% of compression ratio to eliminate most porosities (porosity content 0.61 % ~ 0.71 %) and a maximum compression ratio range of 47% ~58% can be tolerated. Besides, it has a better tensile strength about 222 MPa. For the casting section of 5 mm in thickness, it requires 36% to eliminate most porosities (porosity content 0.61% ~ 0.77%) and a maximum compression ratio range of 48% ~56% can be tolerated. Besides, it has a better tensile strength about 213 MPa.

　　The microstructure observations of AZ91D magnesium alloy in the casting section 10 mm thickness showed that participate, Al12Mg17 is spread continuously in the grain boundaries. After the tensile test, the cross-sections of the fractures show that the fracture mode is intergranular brittle fracture. Increasing of compression ratio to 50%, the fracture mode is combined of intergranular and transgranular fracture, resulting into the increase of tensile strength. Then, the observations of fracture morphology in the section 10 mm thickness of 0% compression ratio reveal that some brittle features are at the fracture surface, and the brittle features are invariable when the compression ratio is increased to 50%.

中文摘要 I
英文摘要 III
目錄 V
表目錄 VII
圖目錄 VIII
第一章 緒論 1
1.1 研究背景 1
1.2 研究目的與內容 2
第二章 理論基礎與文獻回顧 4
2.1 鎂合金簡介 4
2.1.1 鎂合金的命名方式 4
2.1.2 添加合金元素對鎂合金之影響 4
2.2 鎂合金壓鑄的介紹 7
2.2.1 壓鑄法的介紹 7
2.2.2 熱室壓鑄法(Hot Chamber Die Casting) 7
2.2.3 冷室壓鑄法(Cold Chamber Die Casting) 8
2.2.4 壓鑄法的特性 8
2.2.5 鎂合金壓鑄件常見之缺陷及成因 9
2.3 鍛造理論 10
2.3.1塑流應力 10
2.3.2體積不變定律 10
2.3.3 鍛造成形理論 11
2.3.4 材料溫度對鍛造成形性之關係 13
2.5 文獻回顧 15
2.5.1 鋁合金鑄鍛合一 15
2.5.2 鎂合金鑄鍛合一 16
第三章 實驗方法與步驟 24
3.1 鎂合金的壓鑄 24
3.2 鎂合金試片的切割 24
3.3 鎂合金的鍛造試驗 24
3.4 密度及孔隙率的量測 25
3.5 拉伸試驗 26
3.6 微組織的觀察 26
3.6.1 金相觀察 26
3.6.2 破斷面的觀察 27
第四章 結果與討論 34
4.1 鑄造態性質觀察 34
4.1.1 鑄造態孔洞與密度觀察 34
4.1.2 鑄造態微組織觀察 34
4.1.3 加熱到300℃持溫20分鐘對鑄造態微組織的影響 35
4.2 鍛造後性質探討 36
4.2.1 鍛件外觀觀察 36
4.2.2 密度與壓縮率之關係 36
4.2.3 微觀孔洞與壓縮率之關係 37
4.2.4 微組織與壓縮率之關係 38
4.3 拉伸試驗 38
4.3.1 抗拉強度與壓縮率之關係 38
4.3.2 拉伸破斷試片表面觀察 41
4.3.3 拉伸破斷面觀察 42
第五章 結論 76
參考文獻 78

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