BC-MIG Welding for Aluminum Steel Dissimilar Metal Additive Manufacturing

Literature Overview and Research Background

This paper published in the Transactions of the Welding Journal (2015, Vol. 36, No. 7, pp. 5-8) by Miao Yugang and colleagues from Harbin Engineering University presents an innovative approach to additive manufacturing using Back-of-Copper MIG (BC-MIG) welding for joining dissimilar metals. The study uses a 2 mm thick Q235 galvanized steel plate as the substrate and a 1.2 mm diameter 4043 aluminum alloy welding wire as the deposition material. The resulting T-shaped profile structure demonstrates both aesthetic quality and functional performance. This work is significant because aluminum-steel dissimilar joining has long been a challenging problem in engineering due to the formation of brittle intermetallic compounds at the interface, and the additive manufacturing approach offers a pathway to circumvent conventional welding limitations.

Core Technical Findings

The researchers employed metallographic microscopy, microhardness testing, and universal tensile testing to characterize the deposited layer's microstructure, hardness distribution, and shear performance. The most critical finding concerns the interfacial metallurgy at the aluminum-steel boundary. At the bottom of the deposited layer, elongated needle-shaped Fe/Al intermetallic compounds form on the aluminum side, while band-like Fe/Al compounds appear on the steel side. The middle region of the deposited layer consists of dendritic crystals growing upward, whereas the top surface shows no directional growth tendency.

The shear testing results are particularly noteworthy. The aluminum-steel dissimilar metal T-shaped profile can withstand a maximum shear force of 2108 N, with fracture occurring at the root of the build-up layer on the loaded side when the shear angle reaches 13.5°. Importantly, no visible cracks were observed in the build-up layer itself during shear testing, indicating that the interfacial bonding quality is adequate for practical applications.

Technical Parameter Analysis

Engineering Practice Implications

The formation of Fe/Al intermetallic compounds at the interface represents the fundamental metallurgical challenge in aluminum-steel joining. These compounds are inherently brittle due to their complex crystal structures and limited plasticity. The BC-MIG process, by depositing material in a layered manner, allows for controlled dilution and thermal cycling that can manage the thickness and morphology of these intermetallic layers. The needle-shaped morphology on the aluminum side suggests preferential growth along certain crystallographic directions, which is consistent with the known thermodynamic driving force for Fe-Al compound formation during rapid solidification.

From an engineering perspective, the 13.5° shear angle at fracture indicates a moderate degree of ductility in the joint, which is remarkable considering the inherent brittleness of intermetallic compounds. The absence of cracks in the build-up layer during shear loading suggests that the residual stress distribution within the deposited layer is favorable. This finding has direct relevance to the design of lightweight structural components where aluminum-steel hybrid joints are required, such as in marine engineering and aerospace applications.

Study Insights and Reflections

The additive manufacturing approach to dissimilar metal joining represents a paradigm shift from traditional welding. Rather than attempting to create a homogeneous weld zone between dissimilar materials, the BC-MIG process leverages the layered deposition strategy to create a graded transition zone. The directional solidification observed in the middle region of the deposited layer is a natural consequence of the thermal gradient established during sequential layer deposition. This insight suggests that process parameters governing the cooling rate, such as travel speed and layer thickness, could be optimized to further refine the intermetallic layer morphology and improve joint ductility. The practical shear capacity of 2108 N for a relatively small T-shaped profile provides a benchmark for scaling up the process to larger structural components.