MA21合金组织性能及蠕变行为研究
发布时间：2018-08-13 15:56
【摘要】：镁合金由于其密度小、高比强度所以广泛应用于航空航天、国防军事和其他工业领域。作为最轻的结构材料—镁锂合金相比其他镁合金有更高的比强度因而在航空航天上的应用更具潜力。Li元素含量的上升使得Mg合金结构发生转变,提高了其塑性成形能力,而其高温力学性能不佳和蠕变行为还不明确使得其使用受到制约。本文用OM、SEM、TEM、XRD、EDS和EBSD方法对MA21合金组织进行分析;在常温到150℃范围内,对其进行拉伸和蠕变性能测试,并对蠕变后组织进行分析。计算蠕变应力指数和激活能,并以此来判断不同温度和应力状态下的蠕变机制。MA21合金轧制后有一定的晶粒取向性,α相在TD面出现扁平状晶粒,β相较少,包覆在α相周围,两相比为65:35,在α相中有长条状的Al Li相,在β相有小于6μm的粒状析出相,粒径小于200nm的为MgLi2Cd相,粒径在200~700nm的析出相为Mg Li2Cd和Al Li的混和相,粒径大于700nm的混合析出相包含MgLi2Cd、Al Li和Mg Li Zn等;在轧制后(0001)面有较强的织构。拉伸测试结果表明,随着温度的升高,强度下降、延伸率上升,但在从75℃到100℃时出现反常情况,100℃屈服强度高于75℃,延伸率低于75℃,这与不同温度下组织的变化有关。拉伸断口主要呈现出两种断口形貌,α-Mg相以解理平台为主,β-Li相以韧窝为主,随着温度的上升合金的断裂机制发生改变,RT~100℃时,断口形貌主要为解理平台还伴有少量韧窝,125℃以上时解理平台消失,断裂机制从脆性断裂转变为韧性断裂。蠕变性能测试结果表明,温度和应力对稳态蠕变速率有较大的影响。30℃蠕变后,α相中位错密度增大而β相中出现小的析出相增多且有聚集的趋势。在温度小于100℃时,蠕变断口与断裂时应变速率有关,应变速率较快时,会出现少量的解理平台,断裂机制为伴有解理断裂的韧性断裂机制,应变速率较慢时为韧性断裂机制,断裂方式以沿晶为主;在温度大于100℃时,断裂机制逐渐转变为微孔聚集型断裂机制。125℃蠕变后,晶界处出现析出带。MA21合金的蠕变机理受温度和应力的控制,在温度为30℃~100℃时,蠕变应力指数为4~5,蠕变机制主要为位错攀移蠕变机制伴有不连续析出;在温度为125℃和时,蠕变应力指数接近3,蠕变机制为溶质原子拖拽蠕变机制;在150℃低应力下时蠕变应力指数接近2,蠕变机制主要为晶界滑移机制,并伴有出现少量扩散蠕变机制,随着应力的增加,蠕变应力指数接近5,蠕变机制机制变为位错攀移蠕变机制。
[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，
本文编号：2181466
[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，
本文编号：2181466
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