Mg-xSn-yCa合金經ECAE製程之顯微組織與高溫性質研究

Abstract

鎂合金是最輕的結構材，且高比強度、高比剛性、優異的制震性等優點，在汽車 工業中，鎂合金比鋁合金更具有優勢，然鎂合金之加工性差，且高溫機械性質差，因 此鎂合金板材之加工成形性及開發高溫鎂合金成為鎂合金研究之趨勢。 目前最普遍的鎂合金以AZ、AM、及ZK 系列學主，特別是AZ 系鎂合金已很廣泛 運用在3C 組件及汽車構件等領域，但AZ 系鎂合金於高溫時因β相(Mg17AL12)的不穩 定而造成抗潛變性能下降，雖有文獻指出在AZ 鎂合金添加稀土元素(La、Ce 等)以及鹼 土元素(Ca、Sr 等) ，可提升鎂合金的高溫抗潛變性質，但此類稀土元素價格昂貴，不 符經濟效益。 近年來已有學者開始針對較經濟之Mg-Sn 高溫合金系統(其有高溫穩定相Mg2Sn)， 進行諸如機械性質、顯微結構及相變化等研究，雖巳取得初步進展，但相關文獻仍少， 尤其是Mg-Sn-Ca 系合金之研究更少，且對該合金之等通道擠型(ECAE) 、超塑性及潛 變性質幾乎沒有。因此本計畫擬分三年，針對Mg-x%Sn-y%Ca 合金於ECAE 製程後， 其Sn、Ca 含量變化對顯微組織與高溫機械性質之影響，進行系統性的探討分析，第一 年針對高溫拉伸，第二年針對超塑性，第三年針對高溫潛變，以建立該合金系完整之 高溫性質資料庫。

Magnesium alloys are among the lightest metallic materials for structure applications. They have some advantage properties such as high strength-to weight ratio, high rigidity, and good damping capacity. Therefore, Mg alloys are superior to Al alloys for applications of automotive industry. However, Mg alloys exhibit a poor formability and low ductility at room temperature due to their HCP crystal structure and poor mechanical properties at elevated temperatures. Therefore, to research the formability of Mg plate and to develop high temperature Mg alloys are great value. At present, the most popular Mg alloys are AZ, AM, and ZK series. Specially, AZ based alloys have been used popularly to produce 3C components and automotive parts. However, the AZ alloys which are existence of thermal unstable β phases(Mg17Al12) have a poor creep resistance. Some researchers reported that adding rare earth elements (La,Ce etc.) and alkaline earth elements (Ca,Sr.etc.) in AZ alloys can improve the creep resistance. However, the cost of rare earth elements is expensive. Recently, researchers have paid attention to the economical Mg-Sn high temperature alloys which have the formation of stable phase (Mg2Sn) at high temperatures. A few studies focused on the microstructure, mechanical properties and phase transformation of those alloys and obtained some good results. However, little literature has focused on the equal channel angular extrusion process (ECAE) and superplasticity of Mg-Sn alloys, as well as that of Mg-Sn-Ca alloys. Therefore, this study is a three years project which will study the influence of Sn and Ca on the microstructure and mechanical properties at elevated temperatures of Mg-xSn-yCa alloys by using ECAE Process. First year, it plans to study the tensile properties at elevated temperatures; Second year, it plans to investigate the superplasticity; Third year, it plans to study the compressive creep resistance. Finally, we try to establish a complete data base of mechanical properties at elevated temperatures for Mg-xSn-yCa alloys.