連續式六向等徑轉角反覆擠製模具之改良與製程後退火處理之研究

Abstract

自從1994年等徑轉角擠製法(ECAE)提出以來，便被廣泛研究及應用，由於製程不必改變胚料截面積以及能有效率的累積應變能，非常適合用於鎂合金晶粒細化以及材料改質等。 本研究透過模具與衝頭的設計，於衝頭底部增加弧面並增加衝頭與衝頭套之間的空間，使衝頭進入模具時得以自行調整位置，改善衝頭與模具對位不佳所造成的衝頭斷裂以及模具損耗等問題。此外，新設計縮小衝頭與模具通道的間隙，減少擠製餘料的數量以及降低沾黏的程度，ECAE製程效率得以提升。 另一方面，ECAE後搭配熱處理不但能提升AZ31及AZ80的抗拉強度，晶粒大小也呈現雙模態晶粒分佈，延展性得以更進一步的提升。此外，ECAE後的Al12Mg17析出物呈現細小針狀或橢圓狀。不同於一般時效強化所產生的不連續板狀析出物，此形貌析出物能能有效強化材料，還能避免局部區域應力集中所產生的裂紋，所以能維持晶粒細化以及雙模態晶粒分佈所提升的延展性。

In this study, the newly designed punch with the curved bottom and shrunk bottom size introduces more space and be more movable between punch and punch socket, letting it self-adjustable during moving into the mold. By reducing the space between the punch and the mold, the dregs are eliminated efficiently during the extrusion. To sum up, the efficiency of the ECAE process has been improved. On the other hand, ECAE plus annealing will not only raise the tensile strength of AZ31 and AZ80 magnesium alloy, but also increase their ductility. The increasing ductility is due to the bimodal grain size distribution during annealing. Moreover, unlike the discontinuous plate-like precipitates caused by aging hardening, ECAE process can introduce fine needle-shaped precipitates, which allow AZ80 alloy to be simultaneously strong and ductile.