【作者】 杨景红；

【导师】 张禄廷； 田素贵；

【作者基本信息】 沈阳工业大学 ， 材料学， 2005， 硕士

【摘要】 镁合金由于密度小,比强度高等优点而日益受到重视,但其较差的高温性能使其应用受到很大限制。为此,本研究选用AZ31作为母合金,采用元素Sb对其进行合金化,以求改善合金的高温性能。通过对AZ31-x%Sb系列合金的室温、高温力学性能及蠕变性能进行测试,结合OM、SEM和TEM观察,研究了元素Sb对AZ31合金组织与性能的影响及合金蠕变期间的变形机制。 结果表明:AZ31合金经微量元素Sb合金化后,可有效改善合金的高温性能,其中,AZ31-0.84%Sb合金的室温和200℃抗拉强度分别达到297MPa和189MPa。在本实验的应力和温度范围内,合金蠕变期间位错运动的内摩擦应力具有明显的温度敏感性,当温度高于175℃时,内应力值迅速降低;150℃和175℃在50MPa条件下的蠕变期间,合金具有较高的位错运动内摩擦应力,较低的应变速率,其蠕变寿命均大于1200小时;该蠕变规律符合蠕变速率方程 通过该方程及蠕变曲线数据可计算出AZ31-0.84%Sb合金稳态蠕变期间的蠕变激活能为145±10kJ/mol;在不同的应力范围,合金具有不同的应力指数。 AZ31-0.84%Sb合金中析出的高体积分数第二相,是该合金具有较好高温性能的主要原因,特别是高熔点、稳定的Mg₃Sb₂相,弥散分布于合金中,可有效阻碍位错的运动及晶界的滑动。热处理可提高析出相的弥散程度,进一步改善合金的抗拉强度及蠕变抗力,并降低位错运动内摩擦应力的温度敏感程度。微观组织观察及衍衬分析表明:AZ31与AZ31-0.84%Sb合金在200℃、50MPa蠕变期间,主要的变形机制是大量形变位错在基体中滑移,<a>及<a+c>位错分别可在基面、柱面和锥面等非基面滑移,锥面滑移的<a>位错可借助于分解反应,交滑移至另一柱面;在塑性兼容应力的作用下,合金可发生孪晶变形,以多组平行束形式存在的孪晶界可阻碍位错运动,而孪晶区域内晶体取向的微小变化,有利于孪晶内位错的滑移;因此,孪晶作为一种附加的变形机制可改善合金的韧性。更多还原

【Abstract】 Magnesium alloys have attracted increasing attention for potential application in the industries due to their merits of low density and high specific strength and so on. However, the range of the applications for the alloys is limited by its lower strength and poor creep resistance at high temperature. In order to improve the properties of the alloy, the effect of antimony addition on the microstructure and performance of AZ31 alloy, and deformation mechanism during creep have been studied by means of measurement of creep curves, XRD analysis and microstructure observation of TEM.The results show that small antimony additions to AZ31 alloy improve effectively high temperature properties, for example, the ultimate tensile strength of AZ31-0.84%Sb alloy under room temperature and 200℃ is 297 MPa and 189MPa respectively. In the range of the applied stresses and temperatures, the internal frictional stress of dislocation movement for the alloy during creep exhibits an obvious sensitivity to temperature, the value of the internal stress rapidly decreases over 175 ℃. During creep under the condition of the applied stress of 50 MPa at 150℃ and 175℃, the alloy displays a higher creep resistance and lower strain rate, so that the enduring lifetimes of the one are more than 1200 hours. And the creep regularity of the alloy is in accordance with the rate equation given as follows:During steady state creep, the activation energy （Q） of AZ31-0.84%Sb alloy has been calculated to be 145±10 kJ/mol, and there are different stress exponents under the applieddifferent stresses.The fact that high volume fraction of the second phases precipitated in the matrix ofAZ31-0.84%Sb alloy is the main reason for displaying the better high temperature properties. Especially, a large number of Mg₃Sb₂ phases with high melting point areprecipitated homogeneously in the matrix of the alloy, which effectively hinders the movement of dislocations and slipping of the grain boundary during the elevated temperature deformation. The dispersion extent of the second phase distributed in the alloy may be improved by heat treatment, which enhances the ultimate tensile strength and creep resistance, in further, and decreases the temperature sensitivity of the internal frictional stress. By means of microstructure observation and contrast analysis, it is shown that the main deformation mechanism during creep of both AZ31 and AZ31-0.84%Sb alloy is significant amount of the straight dislocation activated in the matrix. The slip of < a > and < a + c > dislocations can be activated, respectively, on basal planes, prism and pyramidal planes. The slip of < a > dislocations activated on the prism plane may cross-slip to pyramidal plane by means of dislocations reaction. Twinning deformation in the alloy may occur in the role of the compatibility stress. Twin boundaries in the form of multiple parallel groups can hinder dislocations movement, but the little change of the crystal orientation in the twinning region may activate again the slip of dislocation within twinning. Therefore, twinning as an additional deformation mechanism may improve the ductility of some alloy with hep structure.更多还原