本文主要目的為探討鎂合金之熱間擠製加工之各種產品的成形性與尋找可獲得最佳機械性質之製程開發，使用田口方法、ANOVA分析、模糊邏輯理論與類神經網路等各種方法，不僅對單一品質特性進行探討，更擴充至多重品質特性之探討，嘗試尋求最適化製程參數組合，並針對各種新產品之研發建立一套可獲得最佳成品之加工參數之預測模式。
本論文共有五項研究主題：(一)應用田口方法與ANOVA分析，探討製程參數對AZ31與AZ61鎂合金管材熱間擠製成品之各種機械性質之影響。將擠製成形之管材進行拉伸試驗與壓平試驗，並針對所得之結果進行比較分析，尋求可獲得最佳抗拉強度之管材熱間擠製製程參數組合，同時探討製程參數對擠製管之顯微組織之影響。(二)探討高擠製比之鎂合金板材熱間擠製加工。由於高擠製比之鎂合金板材需採用變速法，才能擠製出健全之板材，因此在擠製加工過程中須尋找出速度調變時機點。本研究將彙整各實驗結果，引進模糊理論據此來建立模糊理論之預測模式。使用AZ31與AZ61鎂合金在模具半角20°、30°與40°等三組錐度模下，進行板材熱間擠製加工之調變時機點及抗拉強度之預測。(三)結合模糊理論與田口法，探討AZ31與AZ61鎂合金板材之熱間擠製加工時，在兼顧擠製負荷之望小品質特性與抗拉強度之望大品質特性等之多重品質特性指標條件下，尋求最適化製程參數之組合。(四)將產品之型式自管材、板材等擴充至市場上之實際產品，以鎂合金腳踏車攜車架為載具，應用模糊田口方法探討AZ31與AZ61鎂合金腳踏車攜車架之熱間擠製加工，並考慮多重品質特性指標之情況下，尋求壓平強度、T槽破壞強度與擠製負荷之多重品質特性指標之最適化製程參數組合，同時探討鎂合金與鋁合金腳踏車攜車架之機械性質的差異。(五)將上述之實驗結果資料，建立類神經網路分析模式，預測AZ61鎂合金結構件熱間擠製加工後之抗拉強度，並探討在不同材料加熱溫度與擠製速度下，其抗拉強度之變化情形，且將其結果與AZ31鎂合金及A6061鋁合金結構件之機械性質進行比較分析。
本研究中引進模糊理論，配合實驗所彙整之資料庫建立對鎂合金板材熱間擠製之變速時機點與抗拉強度之預測分析模式，能準確的掌握變速時機點與預測成品之抗拉強度，大幅提高實驗之效率。另外，也將模糊理論結合田口方法，針對產品之多重品質特性指標進行分析，尋求能夠以較低之擠製負荷獲得較高機械性質之最適化製程參數組合。依據本研究所進行之各實驗資料所建立之類神經網路之預測分析模式，也可準確的預測擠製後成品之機械性質。希望本研究之成果，能提供鎂合金成形加工之學術界與產業界之研究人員參考。

The main purposes of this study are to investigate the forming behaviors of various products and to develop the optimal manufacturing process for obtaining the magnesium alloys products with good mechanical properties under hot extrusion process. Taguchi method, analysis of ANOVA, fuzzy logic theory and artificial neural network are used, not only to investigate the individual quality characteristic, but expand its application to the multiple performance characteristics index (MPCI) of optimal combination of process parameters. In this study, various new products are produced, and a prediction model of searching optimal combination process parameters of product is established. The five topics are involved in this paper:
1.The Taguchi method and analysis of ANOVA are applied to analyze the influence of process parameters on the mechanical properties of magnesium alloy tubes under hot extrusion. Tensile test and flattening test of the extruded tubes are carried out, and the test results are analyzed to find the optimal combination of process parameters under hot extrusion of tubes. The microstructures of extruded tubes are observed to clarify the influence of process parameters on the grain size.
2.The hot extrusion of magnesium alloy sheet under high extrusion ratio is investigated. According to the former reports, the variable speed method can extrude perfect magnesium alloy sheets under high extrusion ratio. In variable speed method, the speed adjustment timing should be determined before the extrusion experiment. In this study, experimental data of different products are collected, then the fuzzy theory is employed to establish the prediction model of magnesium alloy extrusion. This model is applied to predict the speed adjustment timing and the tensile strength of the AZ31 and AZ61 magnesium alloy sheets under hot extrusion with the semi die angles of 20°, 30° and 40°, respectively.
3.Fuzzy theory and Taguchi method are combined to investigate the hot extrusion process of the magnesium alloy sheets. Not only quality characteristic of the smaller-the-better of the extrusion load but also quality characteristic of the larger-the-better of the tensile strength are considered in the method of MPCI to find out the optimal combination of process parameters.
4.The shapes of extruded Mg product are expanded from tube and sheet to more complicated products of the commercial market. The fuzzy-based Taguchi method is used to obtain the optimal process parameters for the hot extrusion of AZ31 and AZ61 magnesium alloy bicycle carriers by the approach of MPCI. The variables considered in MPCI inference model are flattening strength, T-slot fracture strength and extrusion load. In addition, the mechanical properties of the bicycle carriers made from magnesium alloy and aluminum alloy are compared.
5.According to the data of experimental results an artificial neural network (ANN) analytical model is established, the tensile strength of AZ61 structural parts under hot extrusion is analyzed. Through this analytical model, the influence of billet heating temperature and extrusion speed on the tensile strength of the structural parts are investigated. Finally, the mechanical properties of AZ61 magnesium alloy products are compared with those of AZ31 magnesium alloy and A6061 aluminum alloy.
In this study, the fuzzy theory is introduced to establish the prediction and analysis model for obtaining speed adjustment timing and tensile strength of the magnesium alloy sheets under hot extrusion. It can catch the speed adjustment timing under hot extrusion and predict tensile strength of the extruded parts accurately, eventually the effectiveness of the experiments can be improved. Besides, fuzzy theory and Taguchi method are combined to analyze the MPCI of product. Through MPCI inference model, a fabrication method with less extrusion load and better mechanical properties under hot extrusion can be obtained. According to the experimental data collected in this study, an ANN prediction model can be established, and the mechanical properties of extruded products can be predicted accurately. The models established in this study and analytical results of this study can offer insight to the researchers and industries of magnesium alloy forming.

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