电磁搅拌工艺对AZ31镁合金铸态组织和性能的影响

【作者】 石大鹏；

【导师】 李秋书；

【作者基本信息】 太原科技大学 ， 材料加工工程， 2010， 硕士

【摘要】 中国是世界上镁资源最为丰富的国家,菱镁矿已探明储量约占世界的1/4,具有发展镁产业的先天性基础条件。镁合金作为目前实际应用中最轻的金属材料,以其密度小、比强度高等优良的性能在汽车制造业和3C产品领域中倍受关注,镁及镁合金产品的市场应用前景非常广阔。但目前中国镁及镁合金产业的发展与国外同行业相比较还存在较大的差距,资源优势没有很好的转化为技术优势和经济优势。因此,大力发展镁及镁合金产业对中国的可持续发展将具有异常重要的战略意义。本文以目前使用非常广泛的AZ31镁合金为研究对象,在其凝固过程中施加不同的电磁搅拌工艺,研究了在不同电磁场条件作用下AZ31镁合金的微观组织、力学性能及凝固时间的变化规律。采用金相显微镜和X射线衍射仪对在不同磁场作用下AZ31镁合金的凝固组织进行了观察和分析,结果表明:电磁场对AZ31镁合金的影响非常显著。在交流磁场作用下,镁合金晶粒细化效果非常明显,随着磁感应强度的加强(0.1T~0.2T),AZ31镁合金晶粒细化效果越加明显。当磁场旋转方向进行正反交替变化时所得到的AZ31镁合金凝固组织更加细化,与其他时间间隔条件下比较,改变时间间隔为4S时,电磁搅拌对AZ31镁合金晶粒细化效果更好。当磁感应强度到达0.2T,磁场方向改变时间间隔为4S时,AZ31镁合金晶粒细化效果最好,晶内溶质分布更加均匀。力学性能试验结果表明,电磁搅拌作用下,AZ31镁合金的布氏硬度、抗拉强度明显提高,但伸长率变化不大。合金硬度变化具有一定的规律性,随着磁感应强度的加强,合金硬度呈上升趋势,在同一磁感应强度下,磁场旋转方向改变时间间隔为4S时,合金硬度值最高;随着磁感应强度的逐步加强,合金抗拉强度整体上呈上升趋势,当磁场旋转方向进行正反交替变化时,合金的抗拉强度会进一步得到提升;当磁感应强度达到0.2T,磁场旋转方向改变时间间隔为4S时,合金的硬度值82HB以及抗拉强度140.9MPa达到最佳,布氏硬度和抗拉强度增幅分别达到最高的17%和22.1%。采用热分析法,在不同磁场条件作用下,得到了AZ31镁合金的凝固温度曲线,结果表明:施加电磁搅拌能有效缩短合金的凝固时间,当磁场进行正反交替变化时,能进一步缩短合金凝固时间,磁场强度为0.2T时,合金凝固时间相对较短,磁场方向改变时间间隔为6s时达到最大缩短幅度为21.9%。更多还原

【Abstract】 China is the country which has the most rich magnesium resources in the world. According to the discovery, china has 1/4 reserve of magnesium in the world. Magnesium alloy, which is the lightest metal material in actual application, attracts much attention in automotive industry and 3C product fields because of its excellent physical and mechanical properties. At present, magnesium and magnesium alloy industry in china still have large gaps compare with foreign country. The resources did not translate well to technology and economic advantages. Therefore,it is important to improve magnesium alloy industry in china.In this paper, Magnesium alloy of AZ31 is used as the research object, and different electromagnetic stirring is applied in the process of its solidification. The microstructure, mechanical properties and solidification time of AZ31 magnesium alloy are studied under different conditions.Microstructures of alloys are studied by optical microscope and X-ray diffraction. The result indicates that the effect of revolving magnetic field cause a large decrease in grain size. In AC magnetic field, the grain refinement of magnesium alloys is very clear. When the strengthening of the magnetic induction (0.1T ~ 0.2T), AZ31 magnesium alloy grain refining effect more remarkably. When the rotation direction of the magnetic field to do a regular clockwise and counterclockwise change, the grain of AZ31 will be more refinement; When the time interval is 4S, the electromagnetic stirring on the grain refinement of magnesium alloy AZ31 is the best. When the magnetic flux density reaches 0.2T and the time interval is 4S, AZ31 magnesium alloy grain will be smaller and much more uniform grain distribution within the solute.Mechanical performance test result shows that the effect of electromagnetic stirring can significantly increase the hardness and mechanical properties of AZ31 alloy, but elongation change little. The hardness changes with a regular pattern, when the magnetosphere induction increase, the hardness rise too. In the same magnetic filed, when the time interval is 4S, the hardness is the highest. Increase the magnetic filed, the tensile strength of AZ31 alloy upgrade. When the rotation direction of the magnetic field to do a regular change, the tensile strength of AZ31 alloy will further be enhanced; When the magnetic filed reaches 0.2T and the time interval is 4S, the alloy’s hardness 82HB and tensile strength 140.9MPa are the best, the increase is 17% and 22.1%.The temperature measuring instrument is used in this experiment. AZ31 magnesium alloy solidification temperature curve can be got under different magnetic field conditions. The result shows that: Electromagnetic stirring can effectively shorten the solidification time. When the magnetic field changes the direction of rotation, it can further reduce the solidification time. When the magnetic field is 0.2T and the time interval is 6S, the maximum shortening is 21.9%.更多还原