【作者】 郭洪河；

【导师】 黄尚宇； 刘生发；

【作者基本信息】 武汉理工大学 ， 材料加工工程， 2004， 硕士

【摘要】 镁合金作为结构材料具有其它材料无法比拟的优越性，但有限的机械强度限制了它的推广应用。随着镁合金在汽车工业和IT产业中的应用越来越广泛，对镁合金的研究和应用已经引起各国生产厂商的重视。实践证明，细小等轴的晶粒组织能改善其组织性能，因此找到一种实用有效的晶粒细化剂及处理工艺来细化镁合金晶粒就显得非常重要。 本论文主要针对广泛应用的AZ91合金的晶粒细化工艺及机理进行研究。在AZ91合金中分别加入稀土元素Ce、碱土元素Ca、加交流磁场分别对AZ91和AZ91+0.8％Ce电磁搅拌。对以上几种方法获得的合金组织进行金相观察，并与未处理的AZ91合金的组织进行对比。结果表明，分别加入Ce和Ca后，AZ91合金的晶粒细化效果明显，在本试验条件下，最佳含量分别为：0.8％Ce，0.1％Ca，对应的晶粒尺寸分别减小了58％、43.7％；电磁搅拌能显著细化AZ91与AZ91+0.8％Ce合金晶粒，并产生了球化作用，加入稀土后球化效果减弱，并且有针状新相出现。最佳的励磁电压范围为75～125伏特，对应的晶粒减少了52.6％、41％。此外，对细化机理作了初步探讨。对材料的力学性能进行了测试并与未加细化剂的合金进行比较，表明晶粒细化可明显提高合金的力学性能。更多还原

【Abstract】 Compared with other structural materials, magnesium alloys have many excellent properties, but the poor mechanical properties limit their wide use. With wider and wider applications of magnesium alloys in the automobile and IT industries, the producers all over the world have pay much attention to the researches and applications of the magnesium alloys. It is proved that the refining grain can improve mechanical properties of materials, so it is very important to find an effective grain refiner and technique for magnesium alloys.In this paper, the grain refiner and technique for the AZ91 magnesium alloys are studied by observing their metallurgical structures at as-cast and heat treatment condition. The research methods conducted are adding Ce or Ca to the AZ91 alloy respectively and applying the electromagnetic field on the AZ91 or AZ91 + 0.8%Ce. The results show that Ce and Ca can remarkably refine the grain size of AZ91 magnesium alloy. The optimum content of Ce% and Ca% is 0.8% 0.1% respectively, and the grain size can be reduced 58% 43.7%. As expected, electromagnetic stirring can refine structure of α-Mg phase and lead to action of spheroidization. Compared with the AZ91 alloy, however, spheroidization in the AZ91 + 0.8% Ce alloy is poor, and a new needle-shaped phase precipitate. As the stirring voltage increases, the a-Mg phase size of the AZ91 and AZ91+0.8% is reduced 52.6% and 41%. The optimum voltage range is 75-125 voltage. At last, the mechanical properties of the AZ91 alloy are tested, which proves that mechanical properties of the AZ91 alloy are improved due to grain refinement.更多还原