【作者】 姚亮宇；

【导师】 袁森；

【作者基本信息】 西安理工大学 ， 材料加工工程， 2004， 硕士

【摘要】 镁合金作为工程材料的优点在于：低的密度，良好的刚性、减震性和切削加工性，易于回收利用等。半固态成形是一种可以生产出近终形零件的新型成形技术，所获得的零件的显微组织为球状晶。在制备半固态坯料的几种方法中，SIMA法具有工艺简单、设备成本低的优势。 本文采用SIMA法压缩形变工艺对AZ91D镁合金的形变组织及微观缺陷进行了观测；通过半固态等温液淬实验和挤压成形实验，分析了工艺参数对镁合金半同态组织演化的影响，研究了压缩形变镁合金的半固态球化机制，并与挤压形变SIMA法进行了对比。结果表明： ①形变工艺参数会影响AZ91D镁合金压缩形变组织。形变温度为280℃时，随着形交率的增加，发生脆断和塑性变形的原始枝晶数量增加。形变率为20％时，随着形变温度的增加，原始枝晶发生脆性断裂的数量减少，发生塑性变形的数量增加。枝晶内缺陷以孪晶为主。 ②压缩形变镁合金在半固态保温过程中枝晶的球状化与枝晶内缺陷有关，晶内缺陷促使液相在固相枝晶内部析出，液相沿亚晶界的渗透导致枝晶分解，分解后的晶粒在表面能的作用下逐渐球化；在晶粒球状过程结束后，大的晶粒会随着保温时间的延长而逐渐长大，而小晶粒的数量则逐渐减少；随着等温温度的升高，组织的球状化速度加快，相同等温时间下晶粒的平均尺寸减小。 ③形变工艺参数影响镁合金的半固态等温组织。形变温度为280℃时，随着形变率增加，晶粒尺寸减小。在形变率为20％的条件下，形变温度低于250℃时半固态组织晶粒分布均匀性较差；当形变温度高于250℃时，晶粒分布均匀性明显改善。西安理工大学硕士学位论文 ④将压缩形变与挤压形变制备镁合金半固态坯料相比发现，挤压形变组织中晶粒明显细化;压缩形变晶内缺陷以孪晶为主，挤压形变以位错为主;在半固态等温过程中，挤压形变镁合金晶粒球状化速度明显较快，且所获得球状晶尺寸较小。 ⑤在半固态挤压成形过程中，随着成形温度的升高，镁合金半固态浆料的流变性改善。半固态镁合金组织在高固相率挤压成形过程中会产生形变织构，织构条纹随着成形温度的升高而逐渐舒缓以至消失。更多还原

【Abstract】 The advantages of magnesium alloy being engineered material are as follows: low density, high rigidity, damping capacity, easy machinability and recyclability etc. SSF (semi-solid forming) is new technology to manufacture near net shaped parts with a globular microstructure. Among several processes to fabricate semi-solid billet, the SIMA( strain induced melt activated) process is very simple and advantageous with respect to equipment.In this paper, the Mg alloy specimens for upsetting were studied. The deformation microstructure was observed. Influences of parameters on microstructure of Mg alloy were investigated in semi-solid quenching and forming experiments and the spheroidization mechanism of Mg alloy for upsetting was analyzed in comparison with extruding. The results indicated as follows:(1)There were effects of deformation parameters on microstructure of Mg alloy for upsetting. With the increase of strain at 280*C, the initial dendrite arms of AZ91D alloy got broken or stretched-out; with the rise of deformation temperature under 20% strain, the deformation style of dendritic structure of AZ91D alloy changed gradually from fragmentation to directional bending.(2)In the semi-solid isothermal process, there was evident relationship between thespheroidization of dendrite of deformed AZ91D magnesium alloy and the defect withinthe dendrite caused by deformation, which brought about the precipitation of liquidphase entrapped within solid phase. The penetration of liquid phase along the sub-grainboundary resulted in the separation of the dendrite. The isolated dendrite became globular due to the reduction of the surface energy. After the spheroidization of grains, with the increase in soaking time, the large grains grew up gradually and the quantity of small grains decreased; with the rise of soaking temperature, the rate of grain’s spheroidization got fast and the average dimension of grains diminished.(3)There were influences of parameters on semi-solid microstructure of Mg alloy for upsetting. After holding at 580 for 10min in the semi-solid state, the greater the strain at 280 , the finer and rounder the size of the globular grains of AZ91D alloy and in the mean time, the agglomeration of solid particles deformed at more than 250 got less than that of less than 250 .(4)the differences in microstructure of Mg alloy between for upsetting and for extruding were clear: The average size of grains in deformation microstructure of Mg alloy for extruding was much less than that of upsetting. The main deformation for upsetting was twin and that for extruding was dislocation. In semi-solid isothermal process, the spheroidization of Mg alloy for extruding was faster and the grains were finer.(5)With the rise of temperature in squeeze process, the Theological property of semi-solid magnesium alloy slurry was improved. During the semi-solid forming process, the deformation texture in microstructure of Mg alloy at high solid content was found and the higher the temperature, the less the texture.更多还原