Improved steel/aluminum bonding in bimetallic castings by a compound casting process

• Compound casting process was used to obtain steel and aluminum bimetallic castings.
• Different surface treatment methods were used to produce of bimetallic castings.
• Surface modifier + aluminizing method greatly decreased gaps of the castings.
• Surface modifier + aluminizing method greatly increased bonding of the castings.

Different surface treatment methods of steel inserts, including aluminizing, coating surface modifier as well as a combination of coating surface modifier and aluminizing (surface modifier + aluminizing), were introduced into the fabrication of carbon steel and ZL114A aluminum bimetallic castings during compound casting process. The aluminizing method slightly improved the bonding of the bimetallic casting compared with untreated method, and a gap at the interface was observed, leading to a poor bonding. In the case of the coating surface modifier method, the integrity of the interface was greatly increased because of the improvement of the incompatible between steel and aluminum, which indicated a mechanical bonding without a reaction layer, resulting in a limited improvement of the bonding. While the surface modifier + aluminizing method promoted a sound interface together with a metallurgical bonding, and a reaction layer with an irregular tongue-like morphology and an average thickness of approximately 30 μm was formed, which mainly consisted of Fe2Al5, FeAl3, Al8Fe2Si, and Al2Fe3Si3 intermetallic compounds, resulting in a significant improvement of the bonding.