Bimetallic Material Joining and Machining Risk Control

In the fields of new energy, electric vehicles (EVs), aerospace, and high-end industrial equipment, bimetallic material joining has become a key trend in product development. Engineers leverage the distinct properties of different metals—such as the lightweight of aluminum, the high strength of steel, and the electrical and thermal conductivity of copper—to achieve an optimal balance of weight, performance, and cost. However, bimetallic assemblies also present high machining risks and long-term reliability challenges, requiring mature engineering strategies and process control.

Common Methods for Bimetallic Joining

Depending on industry requirements for mechanical strength, thermal conductivity, weight, and manufacturing cost, different joining methods are employed：

1. Welding

Applicable to aluminum/steel combinations, but large differences in thermal expansion can cause stress concentration, porosity, or cracks at the interface.

2. Extrusion, Riveting, and Mechanical Press-Fitting

Avoids high-temperature issues but requires control of interface indentations, gaps, fixture marks, and contact fatigue.

3. Threaded Fastening

Facilitates assembly and maintenance, but if galvanic corrosion is not managed, service life may be significantly reduced.

Each joining method must be paired with an appropriate machining strategy to ensure overall structural reliability.

Potential Risks in Bimetallic Machining

While bimetallic assemblies offer performance advantages, careful attention is required to mitigate the following risks：

1. Galvanic Corrosion

Contact between metals of different electrical potentials in the presence of conductive fluids (e.g., humidity, salt spray) triggers electrochemical reactions, causing the more active metal to corrode rapidly. Common combinations include Cu–Al, V–Al, Ni–Steel.

2. Machining-Induced Deformation

Differences in hardness, ductility, and elastic modulus result in uneven cutting forces, leading to：

• Dimensional deviations
• Surface defects
• End face misalignment or increased coaxiality errors

Aluminum + steel and copper + aluminum combinations are particularly prone to these issues due to their soft-hard material differences.

3. Interface Fatigue and Microcracks

Under vibration, cyclic loads, or long-term thermal cycling, microcracks can form at the bimetallic interface, gradually reducing overall component lifespan.

Engineering Control Strategies for Bimetallic Machining

To ensure mass-producibility and durability of bimetallic components, engineers typically employ the following strategies：

1. Material Selection and Surface Treatment

Surface treatments can effectively isolate potential differences and enhance corrosion resistance, including：

• Electroplating
• Anodizing
• Oxide films or ceramic coatings
• Insulating coatings

Appropriate coatings not only reduce galvanic corrosion but also stabilize surface hardness and wear resistance.

2. Optimized Machining Sequence

To minimize interface damage and deformation：

• Heavy cutting → performed on a single material first
• Light finishing or surface trimming → performed after final assembly
• Low-stress toolpaths and high-stability fixtures reduce uneven interface forces and dimensional deviations

3. Precision Measurement and Lifetime Prediction

CMM (Coordinate Measuring Machine) + FEA (Finite Element Analysis) can be used to：

• Identify stress concentration areas
• Evaluate interface load behavior
• Simulate fatigue life under different load conditions
• Optimize structure and assembly processes

This workflow is essential for automotive powertrains and aerospace structural components.

Applications and Trends in New Energy, EV, and Aerospace

With increasing demands for:

• Lighter weight
• Higher thermal conductivity
• Higher power density
• Better corrosion resistance
• Greater structural strength

Bimetallic assemblies continue to play a critical role, for example：

• EV motor end caps: Al + Steel
• Battery busbars: Cu + Al
• Aerospace structural components: Ti + Al
• Thermal management modules: Al + Cu

The engineering challenge has shifted from “can it be joined” to “how to maintain stable durability under higher loads and harsher conditions.”

Conclusion

Integration of bimetallic materials forms the foundation of modern precision engineering, but the machining complexity and risks are significantly higher than for single-material parts. Only through rigorous control of material selection, machining sequence planning, surface treatment, and interface design can products in new energy, EV, and aerospace applications achieve reliability, stability, and long-term durability.