Key Takeaways & Executive Findings
- •• Liquid-solid compound casting successfully fabricates A356/6061 bimetallic composites with complete metallurgical bonding when a dense protective layer is applied via chemical zinc deposition and electroplating. • The interfacial microstructure is characterized by equiaxed grains with eutectic silicon at grain boundaries, and the zinc plating thickness does not significantly affect the transition layer microstructure. • Pouring temperature critically influences metallurgical bonding; higher temperatures increase transition layer thickness but slightly decrease interfacial shear strength, with a maximum shear strength of 68 MPa. • The hardness of the bimetallic interface lies between the hardness of the constituent alloys, indicating a gradient property suitable for lightweight automotive applications.
Abstract
A356/6061 bimetallic specimens were prepared by liquid-solid compound casting. The effects of various casting conditions on the interfacial microstructure and mechanical properties of the bimetallic specimens were studied. Results demonstrate that a combination of chemical zinc deposition and electroplating can create a dense protective layer on the surface of the 6061 aluminum bar, achieving complete metallurgical bonding at the bimetallic interface. The interfacial microstructure is primarily characterized by equiaxed grain formation, with eutectic silicon distributed along the grain boundaries. Notably, the thickness of the zinc plating layer does not significantly influence the microstructure of the interface transition layer. Pouring temperature is critical for establishing metallurgical bonding at the bimetallic interface, with the thickness of the transition layer increasing as the pouring temperature rises. The hardness of the bimetallic composite interface falls between the hardness values of the two constituent materials. While the thickness of the galvanized layer has a minimal effect on interfacial shear strength, there is a slight decrease in shear strength with increasing pouring temperature, with a maximum value recorded at 68 MPa.
1. Introduction
Bimetallic composites are innovative materials created through specific manufacturing processes, consisting of a combination of two distinct materials. By synergistically integrating the hardness, thermal conductivity, corrosion resistance, and shear strength properties of these constituent materials, bimetal composites exhibit exceptional physical characteristics and remarkable design versatility [1-3]. Therefore, they are widely used in automotive, aerospace, electronics industries, etc. [4]. The forming technologies for bimetallic composites are diverse, encompassing various methods, including rolling, brazing, dual-flow casting, and liquid-solid compound casting [5-8]. Among them, the liquid-solid compound casting has garnered significant attention in recent years due to their extensive material selection, high productivity, and cost-effectiveness.
A strong metallurgical bonding interface is crucial for the successful fabrication of bimetallic materials. However, achieving a seamless connection between heterogeneous metals is challenging due to the differences in the properties of the two materials and the presence of a natural oxide layer on the surface of the solid-phase material. Extensive studies have been conducted including the adjustment of casting process parameters and the implementation of anti-oxidation protection measures for the solid-phase matrix [9-11]. Liu et al. [12] investigated the effect of extrusion pressure on the microstructure and mechanical properties of the copper-aluminum composite interface. They reported that the thickness of the transition zone gradually decreased with increasing extrusion pressure; however, the tensile strength remained relatively unchanged. Wu et al. [13] established a metallurgical bonding interface between Al and Fe by precisely controlling the melt flow rate and temperature during the die-casting process, with the primary phases of the bonding layer identified as Al60Cu30Fe10 and Fe2Al5.
Notably, aluminum alloys, when used as solid-phase substrates, are more susceptible to oxidation compared to iron and copper substrates. The melting point of the oxide layer is significantly higher than that of the aluminum itself, and this oxidation phenomenon is further exacerbated at elevated temperatures. Schwankl et al. [14] successfully formed a zinc coating on the surface of wrought aluminum alloys through zincate treatment, achieving metallurgical bonding with cast aluminum alloys. This was confirmed by mechanical testing results, demonstrating excellent metal bonding performance. Li et al. [15] conducted a comprehensive investigation on the impact of various surface coatings on the interface microstructure and properties of aluminum/magnesium bimetal castings. The results indicated that aluminum/magnesium bimetallic castings treated with plasma-sprayed nickel exhibited a significant improvement in shear strength compared to those with zinc coatings and nickel-copper composite coatings. Specifically, the shear strength increased by 69% compared to untreated bimetallic castings.
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Chang-li Liu, Peng-fei Xing, Hong Zheng, Qi Gao, Meng-wu Wu (2025). Interfacial microstructure and mechanical properties of A356/6061 bimetal fabricated by liquid-solid compound casting. China Foundry. https://doi.org/10.1007/s41230-025-4231-x
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Frequently Asked Questions
What is the main objective of this study?
The study aims to investigate the effects of casting conditions, particularly pouring temperature and zinc plating thickness, on the interfacial microstructure and mechanical properties of A356/6061 bimetallic composites fabricated by liquid-solid compound casting.
How was the metallurgical bonding achieved in the bimetallic interface?
A dense protective layer was created on the 6061 aluminum bar surface using a combination of chemical zinc deposition and electroplating, which facilitated complete metallurgical bonding at the interface.
What is the effect of pouring temperature on the interface?
Pouring temperature is critical for establishing metallurgical bonding. Higher pouring temperatures increase the thickness of the transition layer but slightly decrease interfacial shear strength, with a maximum shear strength of 68 MPa.
Does the zinc plating thickness affect the interfacial properties?
The thickness of the zinc plating layer does not significantly influence the microstructure of the interface transition layer, and it has a minimal effect on interfacial shear strength.
What are the potential applications of this bimetallic composite?
The A356/6061 bimetallic composite offers a combination of lightweight and mechanical properties suitable for automotive, aerospace, and electronics industries, particularly for components requiring high strength and thermal conductivity.
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