旋转磁场对铸造镁合金组织和力学性能的影响

发布时间：2018-03-07 17:47

  本文选题：镁合金　切入点：旋转磁场　出处：《沈阳工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：电磁搅拌技术对镁合金具有细化晶粒、改善力学性能的作用,但不同搅拌参数下镁合金的组织和性能存在较大的差异。本文以Mg-Al-Zn系镁合金为实验材料,在不同搅拌参数下(改变搅拌频率和磁场电流)浇注镁合金管坯,研究旋转磁场对镁合金显微组织和力学性能的影响。并采用Ansoft和Fluent软件顺序耦合的方法对电磁搅拌作用下镁合金凝固过程的电磁场、温度场进行数值模拟,研究电磁搅拌参数对磁场和温度场的影响规律。研究结果表明:一个周期内旋转磁场在不同时刻的分布规律相同,且旋转周期与电流变化周期相同。随着磁场电流增大,产生的最大磁感应强度和最大电磁力逐渐增大;随着搅拌频率增大,产生的最大磁感应强度逐渐减小,而作用于熔体的最大电磁力逐渐增大。不同搅拌参数下,沿着半径方向,磁感应强度先减小后增大,电磁力逐渐增大。电磁搅拌改变了金属液的换热条件,使镁合金溶液凝固过程温度变化趋于均匀。当搅拌频率6Hz时,磁场电流分别为90A、120A、150A条件下对应的过冷度为2.5℃、4℃、4.5℃,磁场电流越大,AZ31镁合金溶液冷却速度越快越有利于增加形核率,逐渐细化晶粒。当磁场电流150A时,搅拌频率分别为6Hz、8Hz、10Hz条件下对应的过冷度为4℃、5℃、6.5℃,搅拌频率越大,AZ91镁合金溶液冷却速度越快,同样有利于增加形核率,逐渐细化晶粒。磁场电流越大或搅拌频率越大,晶粒细化效果越好,且磁场电流为150A时,AZ31镁合金晶粒内部产生了较多的孪晶,可以提高合金的抗拉强度和屈服强度;β-Mg17Al12相逐渐溶解到α-Mg基体中,形成细小的第二相,并增加了Al原子在基体中的固溶度,可以提高合金的伸长率。磁场电流越大或搅拌频率越大,镁合金的力学性能越好。磁场电流150A时,AZ31镁合金抗拉强度为194MPa,屈服强度为89MPa,伸长率为14.8%,与自然凝固状态相比分别提高23.6%、20.3%和57.5%。搅拌频率10Hz时,AZ91镁合金抗拉强度为164MPa,屈服强度为99MPa,伸长率为5.1%,与自然凝固状态相比分别提高21.5%、19.3%、41.7%。
[Abstract]:Electromagnetic stirring technology can refine the grain and improve the mechanical properties of magnesium alloys, but the microstructure and properties of magnesium alloys under different stirring parameters have great differences. In this paper, Mg-Al-Zn series magnesium alloys are used as experimental materials. Casting magnesium alloy tube billets with different stirring parameters (varying stirring frequency and magnetic field current), The effect of rotating magnetic field on microstructure and mechanical properties of magnesium alloy was studied. The electromagnetic field and temperature field of magnesium alloy solidified by electromagnetic stirring were numerically simulated by Ansoft and Fluent software sequential coupling method. The effect of electromagnetic stirring parameters on magnetic field and temperature field is studied. The results show that the distribution of rotating magnetic field is the same at different times in a period, and the rotation period is the same as the period of current variation. With the increase of stirring frequency, the maximum magnetic induction intensity decreases gradually, while the maximum electromagnetic force acting on the melt increases gradually. Under different stirring parameters, the maximum magnetic induction intensity increases along the radius direction. The magnetic induction intensity decreases first and then increases, and the electromagnetic force increases gradually. Electromagnetic stirring changes the heat transfer condition of molten metal and makes the temperature change of magnesium alloy solution more uniform. When the stirring frequency is 6 Hz, the temperature change of magnesium alloy solution is uniform. The corresponding undercooling degree is 2.5 鈩，

本文编号：1580313