Study Of SIM Solidification And Semi-solid Die-casting Of Mg-9Zn-xAl Magnesium Alloy

In this work, Mg-9Zn-xAl magnesium alloy was studied by SIM rheo-diecasting. Effectof self-inoculation technological parameters on the Microstructure of semi-solid ZA96magnesium alloy was investigated, and the nature of interactive effect between technologicalparameters was analyzed from the standpoint of temperature field. Effect of the melttreatment temperature on the case of inoculants’ melting was analyzed in SIM solidificationprocessing. Influence of isotherm parameters on the microstructure of semi-solid slurry andrheo-diecasting of Mg-9Zn-xAl alloy were investigated. Results show:1. Compared with traditional casting, the grain was refined by SIM. And ethersemi-solid billet was prepared by SIM to meet thixo-forming, or semi-sloid slurry wasobtained by direct isolation to meet rheo-diecasting.2. The ideal melt treatment interval of Mg-9Zn-xAl(x=2,4,6) have to be requiredbetween695℃~710℃、670℃~700℃、660℃~675℃, respectively, and the grain size are49.5μm、42μm、35.6μm, respectively. The average grain size is larger and include a bit ofdentrite when the melt temperature is excessive low or high.3. In SIM casting, microstructure morphology and grain size were influenced byinteraction of technological parameters which include melt treatment temperature、the angleof fluid director and self-inoculants’ addition. Interactive nature of self-inoculation technologyparameters is to obtain high-quality semi-solid billets and slurry by coordinating them.4. According to derived formula which includes T=kΔT+bthat is the temperature ofthe inoculants in the entrance of fluid director, the proper melt temperature can be determinedin SIM casting. The formula between the temperature of melt in the exit of fluid director andself-inoculation technological parameters was derived. What the case of inoculants’ melting isdescribed by solid fraction fs is proposed.5. In isolated processing, the primary phase grow up and globalization with prolongingof holding time. An ideal holding time window has to be required between48min, and thegrain size is65~72μm, and the grain roundness is1.2~1.3. The microstructure of Mg-9Zn-xAlalloy can be refined by Al content, and the grain size become smaller when Al content isincreased.6. In secondary solidification processing, residual liquid with uniform temperature andconcentration fields outbreak the nucleation allover. The nucleation has little chance to growthunder the grate cooling rate, so it forms uniform and fined secondary solidificationmicrostructure. With holding time increasing, the grain size is increasing, and the roundness is decreasing and then increasing, and the solid fraction is improving.