分流擠型為本實驗室新開發之等截面劇烈製程，除了保有先前等截面劇烈加工之特色：1、提供材料相當大之加工量細化微結構；2、加工後材料之截面積不會改變，亦可不斷加工至指定道次才將試片取出。要達到超塑性通常有兩項要求：一為小於10μm之細小等軸晶，其次是在0.5Tm（Tm為熔點溫度）左右之高溫變形。 本研究藉由形態分明之Zn-22wt.%Al共析合金在分流擠型製程中加工，觀察擠製前後微結構之改變，了解分流擠型之流線。並藉由改變擠製道次與溫度條件下，瞭解各截面微結構變化與均勻性，以及對超塑性之影響。 實驗結果顯示出合金經分流擠型製程擠製一道次之流線。微結構則隨著道次增加有逐漸細化與混鍊均勻之效果，且降低擠製溫度可得到更細小之微結構。而材料之超塑性亦隨著擠製道次增加與溫度下降有所提升，於200℃進行高溫拉伸之最佳應變速率為5×10-3s-1，合金經100℃下擠製十道次後，在此最佳初始應變速率(5×10-3)、200℃下進行高溫拉伸，其伸長量可達1092％。 A new cross-channel extrusion （CCE） process of serve plastic deformation can not only provide much strain energy and keep concomitant change in the cross-sectional dimensions but is with continuous processes was developed. The two basic requirements for achieving structural superplasticity are:(1). a fine, stable equiaxed grain size d of less than about 10μm(i.e. d≦10μm) ； and (2). a testing temperature T greater than about one half of absolute melting temperature of the material, Tm(i.e. T≧0.5Tm). Effects of CCE processing with different number of passes and temperature of extrusions on stream line, microstructures and superplasticity of a Zn-22wt.% Al eutectoid alloy were investigated. The results indicated the microstructures became more fine and uniform with increasing the number of passes and were finer with decreasing the temperature of extrusions. The superplasticity after CCE revealed a significant enhancement with increasing the number of passes and decreasing the temperature of extrusions. After 10 passes of CCE at a temperature of 100℃, the elongation at a testing temperature of 200℃ was up to 1092% at an initial strain rate of 5×10-3。
