【作者】 郭峰；

【导师】 李克；

【作者基本信息】 南昌大学 ， 材料加工工程， 2008， 硕士

【摘要】 镁合金具有密度小、比强度高、阻尼性能好及电磁屏蔽等优点,在汽车、电子、通讯等工业领域得到了日益广泛的应用。但是在镁合金的广泛应用中,改善其塑性变形能力仍然是一个非常关键的问题。实践证明,细小等轴晶的组织能提高镁合金的机械性能。因此找到一种实用有效的工艺来细化镁合金的晶粒就显得非常重要。超声波处理作为一种高效、无污染的物理细晶技术,能显著的细化金属的凝固组织。但是至今人们对于超声细化镁合金的研究比较少,因此有必要在该领域内展开深入的研究,并对超声细化镁合金凝固组织的作用机制及工艺参数进行探讨。本文在AZ31B和AZ91D镁合金的凝固过程中进行超声熔体处理,对超声细化镁合金凝固组织的机制及工艺进行了较为深入系统的研究。首先采用了超声物理模拟实验的方法,使用甘油、亚甲基蓝水溶液、NH₄Cl水溶液作为模拟介质进行超声处理,研究了声流、声空化、超声细化的影响因素。结果表明:超声功率、模拟介质温度、超声处理时间、变幅杆位置等影响了超声的声流范围;超声功率、超声处理时间、超声作用的距离等影响了超声空化的强度;超声功率、超声处理时间、NH₄Cl水溶液浓度等影响了NH₄Cl水溶液的结晶过程和晶粒尺寸。其次采用量热法对声功率进行了测定,计算出换能器的平均效率。为了进一步探讨功率超声细化镁合金的机理,本文测定了0W、200W、400W、600W、800W功率超声下AZ31B和AZ91D镁合金冷却曲线。研究结果表明,功率超声提高了凝固开始温度和凝固结束温度,缩短了凝固时间,凝固冷却速率加快。再次,在AZ31B和AZ91D镁合金凝固过程中研究了超声细化工艺参数（超声处理温度区间、超声功率、超声衰减、冷却方式）的影响。实验结果表明,超声连续处理、超声功率为600W、水冷时,对镁合金的细化效果最好。验证了功率超声在金属熔体中存在比较严重的衰减这一物理现象,即超声细化区域是有限的。最后,轧制性能试验证明了超声处理能显著提高AZ31B镁合金的塑性及轧制性能。更多还原

【Abstract】 Magnesium alloys are increasingly applied into the automotive, electronics and communication industries due to their low density high, strength-to-weigh, rigidity-to-weigh ratio, good damping capacity and good electromagnetic shielding properties. However, the key problem to extend the wide application magnesium alloy is to improving deforming ability.Many practices proved that the fine equiaxed crystals structure magnesium alloys could improve mechanical properties. It is very important to find an effective grain refinement for magnesium alloys. Ultrasonic treatment is an efficient and non-contaminative metal refining technique. However, few research on the grain fining of magnesium alloys with ultrasonic in solidification process was done before. Therefore, it needs urgently to carry out a deep-going investigation in this region, which includes discussing the mechanisms of grain fining of magnesium alloys with ultrasonic and the technological parameter. In this paper, the solidification process of AZ31B and AZ91D magnesium alloys was processed by power ultrasonic, and the mechanism and technology of power ultrasonic refinement was widely investigated.Firstly, the method of ultrasound physical modeling experiments was used to study on effects of various factors, such as acoustic streaming, ultrasonic cavitation , on ultrasonic refinement process. And the glycerol, methylene blue solution and ammonium chloride are selected as physical simulation medium of ultrasonic treatment The experimental results show that the effective range of the acoustic stream is different while the ultrasonic power, the medium temperature, the ultrasonic treatment time and the location of ultrasonic amplitude amplifier pole are changed. And the intensity of ultrasonic cavitation is different with changing ultrasonic power, ultrasonic treatment time and distance of ultrasonic amplitude amplifier pole. Also the crystallization of ammonium chloride is different with changing ultrasonic power, ultrasonic treatment time and the concentration of ammonium chloride.Secondly, sound power was measured by calorimetry and efficiency of transducer was calculated. In order to probe into the solidification mechanism of AZ31B and AZ91D magnesium alloys when power ultrasonic was directed into the molten melt, the cooling curves of AZ31B and AZ91D magnesium alloys under 0W, 200W, 400W, 600W and 800W ultrasonic power were measured. The research results showed that the solidifying beginning and end temperature were improved. Furthermore, the solidification time become shorter and the cooling rate of solidification become faster.Thirdly, the effects of processing parameters such as the temperature range, ultrasonic power, attenuation and the cooling mode of ultrasonic treatment on ultrasonic refinement process were researched by introducing power ultrasonic into the solidification process of AZ31B and AZ91D magnesium alloys .The experimental results showed that with continuous treatment, 600w ultrasonic power and water-cooling mode, the finest refining effect on magnesium alloy could be achieved. The ultrasonic attenuation exists along the ultrasonic propagation in the molten metals .And the range of ultrasonic refinement was limited.Lastly, the rolling deforming tests prove that the deforming properties of AZ31B alloy after ultrasonic treatment was enhanced significantly.更多还原