Bimetallic materials generally have superior comprehensive properties which are extremely difficult to achieve for single metal materials [1–3]. Comparing to other bimetal bonding processes, the solid-liquid bimetal compound casting has been extensively used in modern industry with the advantages of good interfacial bonding quality, high production efficiency and wide range of applicable alloys, etc. [4–7]. For instance, the most typical application of this process in automotive is the manufacturing of aluminum engine cylinder block with cast iron liners. Fe-Al bimetallic cylinder block has been a subject of investigation for more than twenty years due to its excellent performance on lightweight and thermal conductivity comparing to the traditional cast iron cylinder block [8, 9].
The challenge of solid-liquid compound casting is the realization of a firmly bonding between two metal components. The characteristic of a real “compound cast” part is the formation of metallurgical bonding interfacial zones where the cast alloy’s components diffuse into the solid material partly via the formation of solid solutions, and partly via the formation of reaction phases [10–14]. It has been proposed that an excellent metallurgical interface is of great importance to guarantee the physical and mechanical properties of bimetallic castings [15–18]. However, due to the difference in the thermal-physical properties, metallurgical bonding is extremely difficult to achieve for compound casting of dissimilar metals. Even for similar metallic couples, owing to the formation of oxide layer on surface of the solid substrate, the wettability between solid-state and liquid-state metals is largely impaired, leading to an incompatible and poor bonding between two metal components [19, 20]. There are a number of attempts to protect the surface of solid substrate metals from oxidation and to obtain an excellent metallurgical bonding between similar and also dissimilar metallic couples. Jiang et al.  found that a surface treatment method of steel inserts, i.e., a combination of coating surface modifier and aluminizing, could promote the formation of a metallurgical bonding interface between carbon steel and ZL114A aluminum alloy during compound casting process. Koerner et al. [22–24] pointed out that wrought Al-cast Al bimetallic castings with flawless metallic interface can be successfully produced by replacing the oxide layer on surface of wrought Al substrate with a zinc layer. Feng et al.  investigated the influence of coating materials on the overcast joining of aluminum alloys and concluded that Ni coating was superior over Cu coating. Ren et al. [26, 27] reported that Al-Mg bimetallic castings could be successfully fabricated by solid-liquid compound casting and they studied the effect of pouring temperature on the interficial microstructure and mechanical properties of overcast joints.
According to literature review, most of the existing research works relating to the solid-liquid compound casting are based on the sand mould or permanent mould casting process. The HPDC process is the preferred choice for the mass production of light metal castings in the automotive, electronics, communications and other fields [28–31]. Comparing to the sand mould and permanent mould casting processes, the much shorter heating and cooling times during the HPDC process represent a great challenge for the solid-liquid bimetal compound casting. Since the time is extremly inadequate for the diffusion and reaction between the two metal alloys during solidification of the HPDC process, it is difficult to achieve metallurgical bonding for bimetallic castings. Accordingly, the fabrication of bimetallic castings by using the HPDC process is still a relatively unexplored area, especially for the Fe-Al bimetallic castings while there are large differences between the two types of metals relating to the thermal-physical properties, including the melting point.
In this study, a practical bimetallic casting consisting of aluminum matrix and cast iron inserts was manufactured by the HPDC process. Different surface treatment methods of the cast iron inserts were adopted to improve the bonding quality of bimetallic castings. Microstructure characterization on the bonding interface of bimetallic castings and simulation of the HPDC process were both conducted, based on which the effects of surface treatment methods and casting process on the bonding quality of bimetallic castings were investigated.