Study On The Influence Mechanism Of Ce-Rich Mischmetal Addition On Solidification Behavior Of AZ91Alloy

In the new century, the human being are faced with numerous challenges such asenergy, resource and environment. It is an effective methodology to develop cleanenergy with advanced science and technology. Rare earth magnesium alloy retain theadvantages of normal Mg alloy, in the meantime, overcome some shortcomings, forinstance, inflammable, bad corrosion resistance and poor mechanical property, turninginto a significant kind of light-type structure material and are applied successfully in agreat deal of engineering fields. Nevertheless, the exiting research mainly concentrateupon the results of, while how rare-earth elements effect Mg alloy solidificationprocess remains unclear, and many underlying issues need to be explored; in addition,some of them are disputed.In the study, the author focused on AZ61and AZ61E. Their Phase transformationpoints were obtained by DSC, then a number of liquid quench temperatures werechosen according to the points. Finally, at the chosen temperature, the rapidsolidification microstructures of AZ61and AZ61E through liquid quench process wereacquired. Adopting reasonable preparation and corrosion methods, employing XRD,OM, SEM and EDS, the rapid solidification microstructures were observed andresearched. Furthermore, the influence mechanism of the mixed rare earth rich in Ce onthe solidification behavior of AZ61based on the solidification theory.The results are as follows:Great condensate depression exit in the liquid quench process of AZ61and AZ61E.Yet it is far from the needed to meet the requirements of nucleation and growth. For thisreason, the liquid quench microstructures achieved under liquid quench temperatureshould not be considered to be the microstructures under the temperature.Because the liquid actual quench microstructure have similarity andcause-and-effect relationships with the ideal microstructure owing to great coolingvelocity, the ideal can be concluded by analyzing the actual, so as to understand andstudy the solidification process and the impact of rare earth elements in thesolidification process.According to the differential thermal curve, the solid-liquid phase change(Lâ†'α-Mg) temperature section of AZ61is from585.1℃to608.1℃, and the eutecticchange (Lâ†'α-Mg+β) temperature ranges between409.8℃and413.2℃. the solid-liquid phase change (Lâ†'α-Mg) temperature region of AZ61E is from585.7℃to608.3℃, and the eutectic change (Lâ†'α-Mg+β) temperature is between409.8℃and413.2℃. After RE is added, it and Al will form intermetallic compound, whichconsumes a part of Al and increases the solid-liquid phase change temperature. So, thetemperature range changes to from585.7℃to604.2℃. Meanwhile, the addition of REimproves the eutectic change temperature, it is because RE can promote the eutecticchange of AZ61, thereby making the temperature range grows between413.9℃and417.6℃.The observation results of AZ61and AZ61E imply that, unlike the previousresearches, the high-melting-point Al-Re phase separated out during solidificationprocess distribute mainly among α-Mg dendritic crystals, but in α-Mg grains high-melting-point Al-Re phase can be barely found. Besides, it can be obviously observedthat the primary-precipitated phase Al-Re impedes the grain growth of α-Mg.