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 the Al

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.