Abstract
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.
Highlights
Bimetallic materials generally have superior comprehensive properties which are extremely difficult to achieve for single metal materials [1,2,3]
Results indicate that compounds with flawless and continuously metallurgical bonding interface can be successfully fabricated by the high pressure die casting (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
It has been reported that the use of a sodium chloride solution or ammonium chloride solution is favorable to the removal of oxide layer generated at the surface of gray iron inserts by chemical reaction [21]
Summary
Bimetallic materials generally have superior comprehensive properties which are extremely difficult to achieve for single metal materials [1,2,3]. Due to the difference in the thermalphysical properties, metallurgical bonding is extremely difficult to achieve for compound casting of dissimilar metals. 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 dissimilar metallic couples. Jiang et al [21] 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 [22,23,24] pointed out that wrought Alcast 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. 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
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