【摘要】：鎂合金由于其密度小、高比強(qiáng)度所以廣泛應(yīng)用于航空航天、國(guó)防軍事和其他工業(yè)領(lǐng)域。作為最輕的結(jié)構(gòu)材料—鎂鋰合金相比其他鎂合金有更高的比強(qiáng)度因而在航空航天上的應(yīng)用更具潛力。Li元素含量的上升使得Mg合金結(jié)構(gòu)發(fā)生轉(zhuǎn)變,提高了其塑性成形能力,而其高溫力學(xué)性能不佳和蠕變行為還不明確使得其使用受到制約。本文用OM、SEM、TEM、XRD、EDS和EBSD方法對(duì)MA21合金組織進(jìn)行分析;在常溫到150℃范圍內(nèi),對(duì)其進(jìn)行拉伸和蠕變性能測(cè)試,并對(duì)蠕變后組織進(jìn)行分析。計(jì)算蠕變應(yīng)力指數(shù)和激活能,并以此來(lái)判斷不同溫度和應(yīng)力狀態(tài)下的蠕變機(jī)制。MA21合金軋制后有一定的晶粒取向性,α相在TD面出現(xiàn)扁平狀晶粒,β相較少,包覆在α相周圍,兩相比為65:35,在α相中有長(zhǎng)條狀的Al Li相,在β相有小于6μm的粒狀析出相,粒徑小于200nm的為MgLi2Cd相,粒徑在200~700nm的析出相為Mg Li2Cd和Al Li的混和相,粒徑大于700nm的混合析出相包含MgLi2Cd、Al Li和Mg Li Zn等;在軋制后(0001)面有較強(qiáng)的織構(gòu)。拉伸測(cè)試結(jié)果表明,隨著溫度的升高,強(qiáng)度下降、延伸率上升,但在從75℃到100℃時(shí)出現(xiàn)反常情況,100℃屈服強(qiáng)度高于75℃,延伸率低于75℃,這與不同溫度下組織的變化有關(guān)。拉伸斷口主要呈現(xiàn)出兩種斷口形貌,α-Mg相以解理平臺(tái)為主,β-Li相以韌窩為主,隨著溫度的上升合金的斷裂機(jī)制發(fā)生改變,RT~100℃時(shí),斷口形貌主要為解理平臺(tái)還伴有少量韌窩,125℃以上時(shí)解理平臺(tái)消失,斷裂機(jī)制從脆性斷裂轉(zhuǎn)變?yōu)轫g性斷裂。蠕變性能測(cè)試結(jié)果表明,溫度和應(yīng)力對(duì)穩(wěn)態(tài)蠕變速率有較大的影響。30℃蠕變后,α相中位錯(cuò)密度增大而β相中出現(xiàn)小的析出相增多且有聚集的趨勢(shì)。在溫度小于100℃時(shí),蠕變斷口與斷裂時(shí)應(yīng)變速率有關(guān),應(yīng)變速率較快時(shí),會(huì)出現(xiàn)少量的解理平臺(tái),斷裂機(jī)制為伴有解理斷裂的韌性斷裂機(jī)制,應(yīng)變速率較慢時(shí)為韌性斷裂機(jī)制,斷裂方式以沿晶為主;在溫度大于100℃時(shí),斷裂機(jī)制逐漸轉(zhuǎn)變?yōu)槲⒖拙奂蛿嗔褭C(jī)制。125℃蠕變后,晶界處出現(xiàn)析出帶。MA21合金的蠕變機(jī)理受溫度和應(yīng)力的控制,在溫度為30℃~100℃時(shí),蠕變應(yīng)力指數(shù)為4~5,蠕變機(jī)制主要為位錯(cuò)攀移蠕變機(jī)制伴有不連續(xù)析出;在溫度為125℃和時(shí),蠕變應(yīng)力指數(shù)接近3,蠕變機(jī)制為溶質(zhì)原子拖拽蠕變機(jī)制;在150℃低應(yīng)力下時(shí)蠕變應(yīng)力指數(shù)接近2,蠕變機(jī)制主要為晶界滑移機(jī)制,并伴有出現(xiàn)少量擴(kuò)散蠕變機(jī)制,隨著應(yīng)力的增加,蠕變應(yīng)力指數(shù)接近5,蠕變機(jī)制機(jī)制變?yōu)槲诲e(cuò)攀移蠕變機(jī)制。
[Abstract]:Magnesium alloys are widely used in aerospace, defense, military and other industrial fields because of their low density and high specific strength. As the lightest structural material, Mg-Li alloy has higher specific strength than other magnesium alloys, and thus has more potential in aerospace applications. The increase of elemental content in mg alloy leads to the transformation of mg alloy structure and the improvement of its plastic forming ability. However, its poor mechanical properties at high temperature and unclear creep behavior restrict its use. In this paper, the microstructure of MA21 alloy was analyzed by means of OMSEMZEDS and EBSD, the tensile and creep properties of MA21 alloy were tested at room temperature to 150 鈩，

本文編號(hào)：2181466