Raytron Technical Review RESEARCH ARTICLE WP-01-08

Heat Treatment: Optimizing Bimetallic Properties

Q: How to determine annealing temperature for bimetallic conductors?

Annealing temperature needs to consider recrystallization temperatures of both metals. CCA annealing temperature should be above aluminum's recrystallization temperature (150-250°C) but below copper's (200-300°C), typically 250-350°C. Excessive temperature leads to excessive IMC growth.

Q: How does heat treatment affect conductivity?

Annealing can eliminate lattice defects and improve conductivity. Conductivity is lower in work-hardened condition and can recover to near theoretical values after annealing. However, excessive IMC growth increases interface resistance and reduces overall conductivity.

Q: How to choose heat treatment type?

Full annealing: choose when maximum ductility and softness are needed; Partial annealing: choose when balance of moderate strength and ductility is needed; Stress relief annealing: choose when maintaining strength while reducing internal stress is needed. Determine based on application requirements.

Gao-Lei Xu¹ *

¹RAYTRON Group Technology Research Center, China

^*Corresponding author

Received: 2025-12 Accepted: 2026-02 Published: 03/2026

DOI: 10.1234/raytron.2026.WP-01-08

Abstract

Heat treatment of bimetallic conductors requires careful control to optimize properties while preventing interface degradation. This study examines annealing, stress relief, and solution treatment processes for CCA, CCS, and NCC, with focus on temperature-time-property relationships.

Key Findings

Annealing Restores Ductility Annealing eliminates work hardening through recovery and recrystallization, restoring material ductility. Annealing temperature is 250-350°C for CCA, 400-500°C for CCS, 350-450°C for NCC, with duration of 30-60 minutes.
Interface Evolution Needs Control During heat treatment, interface undergoes diffusion and intermetallic compound growth. CCA requires control of annealing temperature and time to avoid excessive IMC thickness (<3μm). NCC has better interface stability due to solid solution formation.
Properties are Customizable By selecting different heat treatment processes, mechanical and electrical properties of bimetallic conductors can be customized. Full annealing yields softest condition, partial annealing yields moderate strength, stress relief annealing maintains strength while reducing internal stress.
Atmosphere Control is Important Heat treatment requires protective atmosphere (e.g., N₂, Ar) to prevent oxidation and surface contamination. For CCA, inert atmosphere prevents aluminum oxidation; for NCC, prevents nickel surface oxidation affecting weldability.

Keywords

heat treatment;annealing;stress relief;bimetallic processing;microstructure optimization

1. Introduction

Heat TreatmentControlConductorMechanical properties and conductivity KeyProcess。

2. Annealing Process

Annealing TemperaturePerformanceImpact — **Fig. 1** Effect of Annealing Temperature on Performance

Fig. 2 Recrystallization Process Diagram

3. 4. Aging Treatment

5. Interface Evolution

Interface EvolutionSEMPhoto — **Fig. 3** SEM Photo of Interface Evolution

6. Conclusion

Frequently Asked Questions

How to determine annealing temperature for bimetallic conductors?

Annealing temperature needs to consider recrystallization temperatures of both metals. CCA annealing temperature should be above aluminum's recrystallization temperature (150-250°C) but below copper's (200-300°C), typically 250-350°C. Excessive temperature leads to excessive IMC growth.

How does heat treatment affect conductivity?

Annealing can eliminate lattice defects and improve conductivity. Conductivity is lower in work-hardened condition and can recover to near theoretical values after annealing. However, excessive IMC growth increases interface resistance and reduces overall conductivity.

How to choose heat treatment type?

Full annealing: choose when maximum ductility and softness are needed; Partial annealing: choose when balance of moderate strength and ductility is needed; Stress relief annealing: choose when maintaining strength while reducing internal stress is needed. Determine based on application requirements.

Figures

Create Annealing Temperature on Property Impact Curve

Fig. 1 Annealing Temperature on Property Impact

Re-Crystallization ProcessDiagram

Fig. 2 Re-Crystallization ProcessDiagram

Interface EvolutionSEMPhoto

Fig. 3 Interface EvolutionSEMPhoto

Tables

Table 1 AnnealingParameter

Material	Temperature (°C)	Time (min)	Atmosphere
CCA	250-350	30-60	N₂
CCS	400-500	30-60	N₂
NCC	350-450	30-60	N₂

Table 2 Heat Treatment TypeSelection

Target	Treatment Type	ApplicableMaterial
Softening	Full Annealing	CCA, CCS
Strong	AgingTreatment	CCAA
Stress	LowTemperature Annealing	All

References

ASM International Heat Treating Handbook ASM (2020)

Authoritative References

ASTM International IEC (International Electrotechnical Commission) ISO (International Organization for Standardization) SAE International IEEE

Gaolei Xu

Senior Materials Scientist

Credentials & Honors

• CTO, Raytron Group
• Zhejiang Provincial High-level Talent Special Support Program - Young Talent
• Shaoxing "Technology Vice President"
• Shaoxing Science and Technology Commissioner
• Member of National Technical Committee 243 on Heavy Metals (SAC/TC 243/SC2)

National Standards (Lead Author) View Official

GB/T 27671-2011 - Copper Profiles for Electrical Conductors
YS/T 1043-2015 - Silver-bearing Oxygen-free Copper Strip for Motor Commutators
YS/T 974-2014 - Copper and Copper Alloy Strip for Composite Contact Materials
YS/T 1082-2015 - Copper Strip for Lamp Lead Stents

Patents (Inventor) Search Patents

CN104959396A - Production Process of Copper Strip for Composite Contact Materials
CN106077125A - Production Process of Copper Profile for Magnetic Pole Coils
CN201410710206 - Conductive Material for High-speed Railway Traction Motors and Production Method
CN201310719717 - Method for Controlling Strip Shape of Copper Strip Blank by Continuous Extrusion
CN201310720126 - Device for Controlling Strip Shape of Copper Strip Blank by Continuous Extrusion
CN201310376884 - Five-in-one Copper Strip Edge Treatment Equipment for Transformers
CN201420184755 - Continuous Extrusion Die Flow Promotion Device
CN201320761640 - Continuous Extrusion Waste Cleaning Device

Areas of Expertise

Copper-Clad Aluminum (CCA) Technology Copper-Clad Steel (CCS) Manufacturing Bimetallic Composite Materials PV Ribbon for Solar Cells Battery Tab Materials for EV Applications Continuous Extrusion Technology

Selected Publications

• Research and Application of Rolling Method for Manufacturing Metal Laminated Composites, Aluminum Processing Journal, 2008
• Annealing Process Research of Copper-Aluminum Composite Strip
• Research on Preparation Process of Copper/Aluminum Composite Strip for Cables
• Interface Microstructure Evolution of Rolled Copper/Aluminum Composite Strip During Annealing

Mr. Xu Gaolei is a distinguished expert in non-ferrous metal processing with over 15 years of experience. He is recognized as a Young Talent under the Zhejiang Provincial High-level Talent Special Support Program. He leads R&D initiatives in bimetallic composite technologies and has contributed significantly to the standardization of copper and bimetallic materials in China.

Click standard/patent codes to view official documents