Bonding of cast iron-aluminum in bimetallic castings by high-pressure die casting process

A practical bimetallic casting consisting of aluminum matrix and cast iron inserts was manufactured via high-pressure die casting (HPDC) process. Different surface treatment methods for the cast iron inserts, including salt membrane plating and electrogalvanizing, were adopted to improve the bonding quality of bimetallic castings. Microstructure characterization on the bonding interface was conducted at different locations of bimetallic castings. Results indicate that compounds with flawless and continuously metallurgical bonding interface can be successfully fabricated by the HPDC process with the zinc rack plating treatment on the surface of cast iron inserts which results in a dense zinc coating with an average thickness of 8 μm. The melt flow speed and heat transition during solidification of the HPDC process are two key factors in determining the bonding integrity of bimetallic castings. With the dissolution and diffusion of the very thin zinc coating during solidification, there is no obvious aggregation of zinc element at the metallurgical bonding interface. Instead, a reaction layer with an irregular tongue-like morphology is formed with an average thickness of approximately 1 μm while it mainly consists of intermetallic phases Al₆₀Cu₃₀Fe₁₀, Fe₂Al₅, and Al₂FeSi.