热处理对消失模铸造固-液复合Al/Mg双金属界面组织的影响

Effects of Heat Treatment on Interfacial Microstructure of Solid-Liquid Compound Al/Mg Bimetal Processed by Lost Foam Casting

研究了不同热处理方式对消失模铸造固-液复合Al/Mg双金属界面组织的影响,探索适合Al/Mg双金属铸件的热处理新工艺。结果表明,均匀化退火+空冷的热处理方式会使Al/Mg双金属界面层产生裂纹缺陷,主要由于在较快的冷却速度下,基体和界面金属间化合物的膨胀系数不同,界面处应力较大,易开裂;而均匀化退火+炉冷的方式下Al/Mg双金属界面层未产生裂纹缺陷,且在Al基体和Al_(3)Mg_(2)+Mg_(2)Si反应层间产生了一个由Al(Mg)固溶体+Mg_(2)Si组成的新扩散层。随着均匀化退火时间的增加,新的扩散层厚度不断增加,界面处Al_(12)Mg_(17)+δ-Mg共晶反应层的δ-Mg晶粒尺寸逐渐增大,镁基体中的Al_(12)Mg_(17)相不断固溶到初生相中。多级均匀化退火+时效处理相比于单级均匀化退火更能使界面层的组织和成分均匀,并促使镁基体中的Al_(12)Mg_(17)相呈细小层片状析出。

The effects of heat treatment on interfacial microstructure of solid-liquid compound Al/Mg bimetal processed by lost foam casting was investigated in order to explore the new process suitable for the Al/Mg bimetallic castings.The results reveal that the crack detect appears in the interface of the Al/Mg bimetal after homogenizing annealing+air cooling method,which is mainly attributed to the different expansion coefficient between matrix and intermetallic compound of the interface at a faster cooling rate,and the interface is easy to crack with large stress.While under the homogenizing annealing+furnace cooling condition,the interface is free of the crack defect,and a new diffusion layer composed by Al(Mg)solution+Mg_(2)Si is formed between Al matrix and Al_(3)Mg_(2)+Mg_(2)Si layer.With the increase of the homogenizing annealing time,the thickness of the new diffusion layer is constantly increased,and the grain size of theδ-Mg in theAl_(12)Mg_(17)+δ-Mg eutectic is increased,and the Al_(12)Mg_(17)phase in the Mg matrix is dissolved into the primary phase continuously.Through multistep homogenizing annealing+aging treatment,interfacial microstructure and composition can be more uniform compared to the singlestep homogenizing annealing method,which induces the Al_(12)Mg_(17)phase in Mg matrix to precipitate with a fine lamellar structure.