等徑轉角反覆擠製模具之開發與實驗

Abstract

鎂合金在常溫之塑性變形能力較差，若要克服此缺點，我們可以使用大量塑性變形法來改善。大量塑性變形法不需要改變鎂合金原料的合金成份，只需要採取塑性變形的方式來累積應變量，即可形成各種不同大小的晶尺寸，達到提高塑性變形能力之特性。 大量塑性變形法現階段並未利用在工業生產中，原因為無法連續進行，而文獻中較受關注的連續大量塑性變形法製程均有其的缺點存在。大量塑性變形法中的等徑轉角擠製法原理是利用兩個交角為90°的等徑模具，利用沖頭下壓將材料擠過90°轉角，藉此施予材料應變。此方法的優點在於擠製前後胚料截面積不變，擠製後胚料結構與性質均勻且可應用於大尺寸塊材。但因等徑轉角擠製法無法連續進行，而無法達到最好的細化效果。因此我們將針對上面所發生問題點進行改良，設計出一種全新的模具，在改變不同的製程參數下，找出一個最佳的參數組合，來生產出細化效果最佳的鎂合金胚料，並且可以有效提高生產速率，增加它的商業價值。 將本研究所設計出來的模具，以AZ80為對象進行以擠製溫度、擠製道次、擠製路徑，這三種參數的實驗組合，由這些實驗組合所求出來的數據來找出最佳的晶粒細化參數。並與先前傳統等徑轉角擠製模具實驗時間作比較，可發現新模具確實可使製程時間有明顯的縮短。

Magnesium alloy has poor plastic deformation ability under room temperature, in order to overcome the shortcoming, we can use “severe plastic deformation” (SPD) to improve this ability. SPD adopts the plastic deformation to accumulate the stain, which in turn refines the strain size without the adjustment of the alloy composition. The results lead to the improvement of the magnesium alloy’s plastic deformation ability.

Severe plastic deformation is not used in industrial production, because it can not carry out continuously. Equal-Channel Angular Extrusion (ECAE) is a promising technique for obtaining ultra-fine grain materials with increased strength and ductility. During ECAE, a billet is pressed through a die that consist of two channel with equal cross-section, intersecting at an angle. The cross-sectional shape of billet remains nearly unchanged in ECAE process, properties and micro-structure in the billet are very uniform after extrusion, it is often applied to large size piece of material. However, ECAE can not be carried out continuously to achieve the best results of refinement. Therefore, we design a new mold to achieve this result.

In this study, we design the new mold, applied it to AZ80 magnesium alloys, conducted experiment with this mold to find the best parameters combination for grain refinement. We found the new mold significantly reduce the time for continuous ECAE.