| 摘要: | 商業用5083鋁合金，具有低密度、強度適中、抗腐蝕性良好及焊接性佳等特點，透過輥軋式熱機處理製作成鈑材後，成為最常被使用在結構材上的細晶超塑性鋁合金；近幾年來，另一種嶄新的晶粒細化技術，等通道彎角擠製（ECAE）被廣泛的研究應用在許多的鎂合金及鋁合金方面，但是對於5083鋁合金的研究卻未多見。本研究應為首次對5083鋁合金實行ECAE，共應用4種ECAE製程參數及不同批次生產的5083鋁合金，探討ECAE製程參數及合金元素對擠製後微結構及機械性質影響，另外也比較ECAE及輥軋兩種製程的晶粒細化效果。 5083鋁合金經過90°-200℃-Bc8擠製後，能產生小於1μm之等軸次晶粒結構，Fe含量較低的5083鋁合金並且在250℃及450℃的溫度下，使用1×10-3 s-1的應變速率，分別得到266.6%及350%的伸長量，同時具有低溫及高溫的超塑性。此外，5083鋁合金經過ECAE製程後，初始的〈110〉// ND的ζ-fiber完全消失，轉變成為類似扭轉變形時產生的〈111〉// ND的剪力織構，除了擠製溫度之外，剪力織構的強度取決於剪切平面的數量與夾角，使用Φ=120°的織構強度會高於Φ=90°，而且各擠製方位剪力織構強度的表現Route C>Route A>Route Bc。 ECAE製程參數的影響，除了使用較小的通道夾角，可以施加較大剪應變於材料之外，不同的擠製方位、擠製溫度及擠製道次，也會導致微結構產生不同的晶粒形狀、晶界性質、織構組成及強度，這些因素主導著低溫超塑性期間，動態再結晶的出現與否。高溫超塑性期間，Mn、Fe、Si元素組成的第二相顆粒，扮演非常重要的角色，Fe含量較少的第二批5083鋁合金，在450℃的拉伸測試中，可以獲得較高的m值與最佳的伸長量。 Commerical avaiable 5083 Al alloy is well known for its good weldability, corrosion resistance and medium strength with ductility. It was one of the few aluminum alloys that had been targeted for developing fine-grained superplasticity for structural applications through rolling type thermo-mechanical process. In recent years, a new technique for refining grain sizes, equal channel angular extrusion (ECAE) has been emerged and imposed on many magnesium and some aluminum alloys. Surprisingly, it is seemingly not involving the Al-5083. In this study, billets extruded by ECAE using four kinds of process parameters will be prepared for microstructure observations and mechanical property tests. Furthermore, two batches of 5083 Al alloys containing slightly different on composition will also be compared after ECAE. The microstructure of 5083 Al alloy processed by 90°-200℃-Bc8 condition is consisted of equaxied subgrain structure, and grain size is small than 1μm. The elongations of 5083 alloy containing lower Fe that tested at initial strain rate 1×10-3 s-1 are 266.7% and 350% at 250℃ and 450℃, respectively. The restult shows that 5083 Al alloy reveals low and high temperatures superplasticity simultaneously. After ECAE, the initial texture of 〈110〉// ND of materials disappeared completely and were translated into 〈111〉// ND shear texture which was also formed in torsion processed material. Besides extrusion temperatures, the amount of shear planes and an included angle between them also affect the intensity of shear texture. The intensity of shear texture at die angle Φ=120° is higher than Φ=90°, and Route C>Route A>Route Bc. Using different process parameters, such as Routes, temperatures and number of passes, which will lead to microstructure having different grain shapes, grain boundary properties and texture components. These characteristics will control whether dynamic recrystallization occurs or not during low temperature superplasticity. During high temperature superplasticity, the second phase particles consist of Mn, Fe and Si elements, which play an important part for tensile testing. The 5083 Al alloy containing fewer Fe which represents higher m-value and optimum elongation at 450℃. |
