Al-Mg-Si系鋁合金具有高比強度及高抗腐蝕性，因能源價格高漲而大量應用於交通運輸工具上，以期節省能源消耗；為了提升金屬加工成形性以製備複雜工件，衍生出半固態製程，其為將材料置於半固態條件下加工成形之技術，成品具有近淨形之優點。
半固態製程中的SIMA製程之最大優點，在於技術門檻與投資金額相對低廉。本研究利用單純擠型做為導入應變能之媒介，改良傳統SIMA製程之缺點，並探討不同累積應變量之母材於SIMA處理後微觀組織之變化，以釐清球狀晶的演變機制；此外，本研究亦針對經鹽浴熱處理之SIMA材進行室溫至600°C之拉伸測試，探討其拉伸性質，以作為未來應用於鋁合金高溫成形製程之參考。
實驗結果顯示，經由單純擠型取代傳統冷壓縮加工段之改良式SIMA製程，可確實製造出具有等軸球狀晶組織之半固態胚料；選用累積應變量較高之擠型材，可有效縮短改良式SIMA製程之鹽浴熱處理時間，獲得SIMA材之球狀晶胞徑也較小。
初始晶粒形態為等軸細晶之母材，於SIMA初期會發生grain coalescence成為長軸狀晶粒，待液相生成並穿透高能量晶界串連，晶粒被液相包覆成為晶胞而球化。隨著持溫時間增加，晶胞以Ostwald ripening逐漸粗化，液相聚集成液相池以降低總表面能，最終成球狀固相晶胞存在於液相基地之特徵組織；除此之外，累積應變量愈大之母材，其晶胞粗化速率愈小。
材料拉伸性質方面，於室溫下裂紋沿晶胞界之過冷液相傳遞，破壞行為屬於脆性穿晶破壞；隨著拉伸溫度增加，材料拉伸強度逐漸降低，過冷液相晶胞界逐漸由脆性轉延性，但其仍為裂紋主要傳遞路徑。SIMA材之延性於300°C以上明顯提升，主要為球狀晶胞沿拉伸方向伸長變形所貢獻；但拉伸溫度為600°C時，SIMA材之過冷晶胞界重熔成液相，些微拉力即可造成材料破壞，故半固態SIMA材藉由張應力成形之製程技術仍需進一步評估。

Al-Mg-Si alloys with high specific strength and corrosion resistance are widely used in automotive application in order to reduce energy consumption. In order to enhance the formability of the alloys for fabricating the complex components, the semisolid processes which have the advantage of near-net-shape product were introduced.
The most advantage of SIMA process, one of semisolid processes, is the relatively simple technical barriers and low investment costs. In this study, the simple extrusion was applied to induce strain to improve the defect of traditional SIMA process applied cold compression. And the effects of accumulated strain and isothermal soaking time were investigated in order to clarify the evolution mechanism of globular grain structure.
Furthermore, in order to investigate the tensile properties of SIMA alloys, the materials via salt bath heat treatment of the newly modified SIMA process were undertook tensile test from room temperature to 600°C. The results of tensile test could be applied as the assessment of high temperature forming processes in the future.
According to the results of the experiments, it could be fabricated semisolid billet with characteristic structure of equiaxed globular grain via the newly modified SIMA process applied simple extrusion instead of cold compression. The required time of salt bath heat treatment of alloy with higher accumulated strain could be reduced efficiently, and the grain size of SIMA alloy also decreased.
At initial stage of SIMA process, the recrystallized fine grains coalescenced into elongated grains. With the increase of liquid fraction, the liquid phase penetrated high angle boundaries and solid grain were surrounded. With the soaking time increase, the dominant mechanism of grain coarsening is Ostwald ripening, and liquid phase gathered to form liquid pool to reduce the total interface energy between solid and liquid phases. Besides, the higher the accumulated strain of alloys is, the lower the grain coarsening rate is.
On the aspect of tensile properties, the cracks propagated along supercooled liquid phase grain boundary at room temperature, and the fracture structure belongs to brittle manner. With the increase of tensile temperature, the tensile strength gradually decreased. Although supercooled liquid boundaries gradually turned ductile from brittle with increasing temperature, boundaries were still the main propagating path of crack.
The ductility of SIMA alloy increase significantly above 300°C, the main contribution is the elongation of globular grain along tensile direction. However, the SIMA alloys could not stand tension at 600°C due to the remelting of boundaries. It is necessary to further evaluate the feasibility of forming process of semisolid SIMA alloys by tension.

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