| 摘要: | 中文摘要 金屬超塑性依據產生的機理可以分成組織超塑性、相變超塑性和應力誘發超塑性三類。而鋁合金超塑性則屬於細晶超塑性，其材料的超塑性質受晶粒大小所影響，相對的也主導著其高溫潛變特性。因此如何細化鋁合金晶粒可視為鋁合金快速成形技術發展之重要條件。本研究為改善高強度鋁合金之性質以擴展其應用性，分別針對析出硬化型之高強度鋁合金7039、7049加鈧研究其對晶粒細化與高溫拉伸潛變特性，以及非析出硬化型鋁合金5083經等通道彎角擠製與氣壓快速成型之超塑性成型特性加以探討。 研究結果顯示：AA7039在添加微量Sc後，常溫抗拉強度無論有無經過退火皆有400MPa以上的表現，而AA7049在添加Sc、Zr和Cu後，其抗拉強度為522MPa，且兩者皆在滾軋率R=20%有較強之抗拉強度。而120、150℃溫度下之人工時效T6處理之拉伸試驗結果則顯示：AA7049加Sc、Zr和Cu之抗拉強度高達660MPa比AA7039加Sc之抗拉強度466MPa抗拉強度提升許多，主要是其結構上含有散佈強化和析出物較多。在高溫拉伸部分，AA7039加Sc在溫度400℃以應變率1×10-2下，伸長量124%為最佳效果。AA7049加Sc、Zr和Cu在溫度400℃以應變率5×10-3，伸長量可達244%。主因在於含有較多晶粒細化劑Sc、Cu和Zr。並且由金相圖中可明顯觀察到AA7049加Sc、Zr和Cu經過500℃、1hr退火，晶粒有明顯的細化現象且有消除擠製流線的作用。 5083 鋁合金經過90°-200℃-Bc8條件之等通道彎角擠製後，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。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、晶界性質等，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。 在研究快速超塑性製程之成型機制方面：5083 鋁鎂合金鈑片利用雙面塗有T50-66 潤滑劑的一個杯狀盒子模具ψ40mmx20mm 深，在溫度500℃做階梯式增壓吹氣成型的完全成形時間為70 sec，得到令人意外的結果，成形時間遠比傳統氣壓成型的操作成形時間少了幾十倍之多。由成型溫度400℃、450℃、500℃的試驗結果以500℃之成形性最佳。成形過程中的應變率分佈，溫度400℃、450 ℃與500℃在成形的各個階段，其中觸底階段高達10-1 s-1，比傳統的10-3 s-1快了非常多。空孔的分佈情形是以單位面積的空孔率做比較，400℃空孔嚴重，其單位面積的空孔率為11.69％，而450 ℃與500℃的空孔明顯減少許多，450 ℃的單位面積的空孔率為2.57％，500℃的單位面積的空孔率為3.54％。依綜合成形時間、成形過程中的應變率分佈、厚度分佈均勻度、空孔分佈情形等結果的比較我們可以明確的得到，500℃的操作溫度，為最佳的操作條件。 Abstract Aluminum alloys have been generally used because of its opposite strength, light weight, high heat and electric conductivity, superior ductility and easily tomanufacture. One’s early years, Soviet bring up that aluminum alloys have perfect mechanical properties when adding scandium into alloys. This approach has more and more emphasis recently and is used for the frame of bicycles, the head of golf club and so on. The experiment adopts A7039 alloy and A7049 alloy which are all added about 0.05wt.% and 0.106wt.% scandium respectively.Metal plate is processed by rolling and metal plate changes the rolling reduction ratio and changes the temperature of elongation. By way of changing these parameters, we aspect this method can promote the strength of materials and improve the breadth of 7000 series of aluminum alloys which are added scandium. The experiment result exhibit that the tensile strength of A7039 alloy and A7049 alloy can promote to 466 MPa and 660 MPa , and elongation can promote to 124% and 244% , at 400℃ by strain rate 1×10-2 and 5×10-3 respectively.We can know that all of the mechanical properties are obvious be promoted when the temperature is 400℃. When R=20％, the maximum yield strength of room temperature is about 400MPa and 522 MPa respectively. Although the regular AA5083 Al alloy has long been used, its superplastic version has not been intensively or thoroughly studied such that some aspects regarding superplastic AA5083 are unclear. For example, the influence of Fe content on superplastic elongation is almost neglected, and this topic will be explored. Besides, this paper presents one of the minority studies on applying the equal channel angular extrusion (ECAE) to this alloy. It provides a comprehensive knowledge of processing and thus resulting mechanical properties as well as microstructures, which are probably unavailable elsewhere.This paper represents a large scale of experimental work in using the ECAE process on two groups of the AA 5083. There had been high expectation on the ECAE in greatly refining grain size in order to result exceptional superplasticity as most references indicated. However, our large amount of processing and subsequent tensile testing at various conditions did not fully confirm this common impression. The best superplasticity obtained is 350%, which is no superior to the commercially available rolling-type AA5083. Effect of lubrication on deformation behavior of a superplastic material has been given little attention, although it is important for industrial application. In this paper, a superplastic 5083 Al alloy under bi-axial deformation was investigated by deforming the sheet into a cylindrical die cavity with and without lubrication. Several interrupted tests were performed to bulge the sheets to various depths for two different strain rates, the formed parts were then utilized to evaluate the effect of lubrication on metal flow, thickness distribution, and cavitation. It was found that reducing the interfacial friction by use of a lubricant improved the metal flow after the deformed sheet had made contact with the bottom surface of die. Changes of the metal flow during forming not only developed a better thickness distribution of the formed part, but also reduced cavitation levels. |
