【作者】 王明星；

【导师】 周宏；

【作者基本信息】 吉林大学 ， 材料加工工程， 2008， 博士

【摘要】 利用工业上普遍应用的AZ91D和AM50B镁合金作为原料,在合金中以复合形式分别加入Y和Ce稀土元素、金属Sr和Y、金属Sr和Ce,研究它们的复合作用对镁合金组织性能的影响。还通过在AZ91D和AM50B及复合处理镁合金凝固过程中施加不同振幅的机械振动,来研究机械振动对镁合金组织、性能以及对合金中夹杂物分布、尺寸、形状的影响。研究结果表明,在本实验范围内,在合金熔炼过程中复合加入稀土元素(Y和Ce)以及金属Sr和Y(Ce),能够明显细化合金微观组织,并且显著提高合金力学性能。在AZ91D、AM50B镁合金的凝固过程中施加不同振幅的机械振动,能细化合金铸态组织,提高合金力学性能,同时还可以使合金中夹杂物下沉,减小夹杂物的尺寸以及改善夹杂物形状。对稀土锶复合镁合金的凝固过程施加不同振幅的机械振动后,合金铸态组织在添加微量元素的基础上得到了进一步细化,其力学性能进一步提高,并且随着振幅的增大,力学性能呈逐渐提高的趋势。根据实验结果,开发了机械振动沉降合金中夹杂物再将其截去净化镁合金的方法,设计机械振动用铸锭浇注模具,并将其应用在铸锭生产中。更多还原

【Abstract】 With low density,relatively high intensity and stiffness,easier cutting processing capability and good shielding properties,magnesium alloy is recently used in most of industries,such as, automobile,electronics, aviation,etc.Researchers devote themselves to the production technology of magnesium alloy and abtain some results.However,nearly there is few research in the relationship of structure property and capability with materials and mechanical vibration with different amplitude. In fact,they does tie up.The mechanical vibration with different amplitude has an important impact on structure and property of magnesium alloys.In this article the impact on structure and property of the different amplitude, the shape、size、amount of inclusions in different amplitude,The impact on structure and property of magnesium alloys after vibration of different content of RE(Y、Ce) and Sr were studied.Re-melt AZ91D and AM50B magnesium alloys,and analyzise the changes of structure and property of magnesium alloys after mechanical vibration with different amplitude in the process of solidification, the shape、size、amount of inclusions were also studied.As a result,it was found that the the structure and property of magnesium alloys has great changes after vibration.α-Mg grain size was refined obviously. It is obvious that the shape ofβ-Mg17Al12 changes from mesh(AZ91D)and bone-shaped(AM50B) distribution to massive and point distribution. In this experiment,with the increasing of amplitude the microstructure of alloys was refined,the sinking mount of inclusions in alloys was great.By researching the size,shape of inclusions in alloys in the biggest point of inclusion volume fraction more than,we found small and circular inclusions were more than another.In addition, AZ91D and AM50B magnesium alloy were added 0.3 wt.% Y and 0.08 wt.% Sr and divided into 6 groups and imposed 0 mm, 0.5mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm amplitude mechanical vibration in the solidification process to study the changes of structure and mechanical property of AZ91D and AM50B magnesium alloy containing Y, Sr after different amplitude mechanical vibration . The results show that AZ91D and AM50B magnesium alloy containing 0.3wt.%Y, 0.08wt.%Sr has emerged in the Al2Y and Al4Sr new phase, casting structure obviously can be refined, the original mesh and bone-shaped distribution ofβ-Mg17Al12 part of a network fault and fracture. Application of different amplitude mechanical vibration, the as-cast structure was further refinement,β-Mg17Al12 fracture region increase. With gradually increasing of amplitude the matrix grain size of alloys decreases, theβ-Mg17Al12 in AZ91D off from the local network into a massive network of fully broken, dispersed in theα-Mg matrix. theβ-Mg17Al12 in AM50B off from bone-shaped distribution into the point and dispersed inα-Mg matrix. The mechanical properties of AZ91D and AM50B magnesium alloy added 0.3 wt.% Y and 0.08 wt.% Sr than not adding Y, Sr increased significantly. However, the mechanical properties of AZ91D and AM50B magnesium alloy after mechanical vibration with different amplitude has a gradual increase with the rising amplitude .Within the scope of the trial, when the amplitude is 2.5 mm, the mechanical properties of alloy is maximum.Added rare earth elements (Ce and Y) , Sr and Y (Ce) to the alloy and impose mechanical vibration with amplitude of 2.5 mm in solidification process, research the effect of micro-alloy element on magnesium alloys after vibration adhering the principles of "multi-trace" .The results show that, in the absence of vibration, add trace elements Y, Ce, Sr to AZ91D and AM50B magnesium alloy, emerged in needle-like Al11Ce3, Al4Sr and lumpy Al2Y new phase. As-cast structure with increasing of Y, Ce, Sr content significantly refined, but with the Y, Ce, Sr content further increase,the structure of AZ91D and AM50B magnesium alloy gradually coarse. But in the solidification process ,imposing mechanical vibration with amplitude of 2.5 mm, the as-cast structure was refined with Y, Ce, Sr content was gradually increased. The mechanical properties of alloys with Y, Ce, Sr adding elements also increase. By comparing alloy microstructure before and after vibration found, the Al11Ce3 in not-vibration AZ91D and AM50B magnesium alloy is long, coarse needle-like phase, but after vibration the most of Al11Ce3 were crumbled into globular ,which is conducive to further refine grain, to improve the mechanical properties of alloys.Mechanical vibration has great effect on forming and growth of crystal in magnesium alloys. Vibration increases undercooling of the alloy, which result in increasing the number of spontaneous core, so these grains were refined and mechanical properties were increased. The stir of mechanical vibration makes the grains collide and dendrite loss, which result in increasing the number of crystal and refining the grains size. Furthermore, vibration made the distribution of solute more symmetrically, which resticted the growth of crystals. Vibration has great effect on sedimentation of inclusions, and inclusions with large size have fastr sedimentation rate than those with small size. Vibration promote the decreasing of free energy of inclutions interface, so shape and size of inclusions were varyed. And data and result of the researth were used to design gravity casting moulds. These mould were applicated in production of casting ingot with few inclusions.更多还原