导流器对自孕育铸造法制备AM60镁合金半固态浆料的影响(Ⅲ)

采用自孕育铸造法制备AM60镁合金半固态坯料,研究导流器参数对半固态组织的影响规律及组织形成机理。结果表明:导流器能有效促进合金组织由树枝晶向等轴晶及颗粒状晶的转变;熔体处理温度和孕育剂加入量一定时,导流器的相关参数,如角度、长度、温度、混合段的凹槽宽度,均影响合金的传热及流动,进而影响其凝固组织;在导流器角度为30°～45°、长度为500 mm、混合段凹槽宽度为50 mm、且通水冷却时可以获得细小颗粒状或蔷薇状的半固态坯料,初生α-Mg的平均晶粒尺寸为37.5μm;减小导流器出口宽度有利于增强液体紊流,促进晶粒均匀分布;导流器促进了熔体非均质形核及激冷晶的形成,增强了晶粒增殖;熔体对流使合金的温度场和浓度场更均匀,晶粒生长以颗粒状生长、蔷薇晶根部颈缩熔断和磨圆熟化机制为主。

Effect of cooling channel on AM60 Mg alloy semi-solid slurry prepared by self-inoculation method (Ⅲ)

The semi-solid slurry of AM60 Mg alloy was prepared by a novel self-inoculation method(SIM).The effects of the cooling channel parameters on the microstructure and microstructure formation mechanism were investigated.The results show that cooling channel can promote the microstructure evolution from coarser dendrite to rosette or small block.At the constant value of melt treatment temperature and addition amount of self-inoculants,the parameters of fluid director,such as slope angle,length,temperature and width of exit,have influence on the heat extraction and shear intensity of melt flow,and finally affect the solidification microstructure.When the cooling channel parameters are set at angle between 30°-45°,length of 500 mm,width of exit of 50 mm and water cooled at the bottom,the semi-solid billet with refined rosette or small block microstructure is produced,and the average grain size is 37.5 μm.The decrease of the exit width leads to uniform distribution of grains.The cooling channel enhances the heterogeneous nucleation and formation of chill grains,which results in a high grain density.The melt convection leads to uniform distribution of temperature and solute field in bulk melt.The granular and rosette-like growth and the ripening of grains are the main growth mechanism.