Molybdenum-copper thin sheets, as high-performance composite materials, combine the high melting point and high strength of molybdenum with the high electrical conductivity and high thermal conductivity of copper. They are widely used in fields such as electronic packaging, aerospace, and high-temperature industries. However, due to their complex material properties, issues like cracking and oxidation are prone to occur during the processing. Therefore, mastering the correct processing techniques is of utmost importance. This article will provide a detailed introduction to the processing methods and key techniques for molybdenum-copper thin sheets.
1. Powder Metallurgy Method: Uniform Structure and Purity Guarantee
The powder metallurgy method is the mainstream approach for preparing molybdenum-copper thin sheets. Its core lies in obtaining products with a uniform structure and high purity by precisely controlling the powder ratio and sintering process.
1.1 Blending and Mixing
Mix molybdenum powder and copper powder according to the preset ratio, and add 0.15% – 1% of a binder (such as paraffin wax or polyvinyl alcohol) to enhance the powder’s fluidity. The mixing process should be carried out under the protection of an inert gas to prevent oxidation.
1.2 Drying and Screening
Dry the mixed powder at 80 – 120°C to remove moisture. Then, screen it through a 20 – 160 mesh sieve to ensure uniform powder particle size.
1.3 Roll Forming
Adopt the powder-bonded rolling technique to compress the mixed powder into a raw sheet blank with a thickness of 0.3 – 2 mm. During rolling, control the pressure to avoid interlayer separation.
1.4 Sintering
Under vacuum or hydrogen protection, heat the raw sheet blank to 1300 – 1400°C for sintering to densify the molybdenum-copper particles. The cooling rate after sintering should be slow to reduce internal stress.
1.5 Subsequent Processing
Depending on requirements, perform 1 – 6 passes of cold rolling or warm rolling at 30 – 300°C on the sintered thin sheet to obtain molybdenum-copper foil with a thickness below 0.1 mm. During cold rolling, multiple annealing processes (e.g., holding at 600°C for 1 hour) are required to eliminate work hardening.
2. Roll-Bonding Method: Efficient Bonding and Performance Optimization
The roll-bonding method combines molybdenum and copper sheets through high temperature and high pressure, which is suitable for preparing thick-gauge molybdenum-copper composite sheets and then obtaining thin sheets through subsequent processing.
2.1 Surface Treatment
Use sandpaper to polish the bonding surfaces of the molybdenum and copper sheets to remove the oxide film. Then, perform ultrasonic cleaning to ensure a clean interface.
2.2 Stacking and Fixing
Stack the sheets in the order of copper/molybdenum/copper, fix them with rivets, and grind the edges to a 15° – 30° bevel for easy entry into the rolling mill.
2.3 Heating and Rolling
Under argon protection, heat the stacked sheets to 750 – 850°C and immediately roll them. Control the single-pass reduction rate at 60% – 70%, and the total deformation should exceed 80% to achieve a firm bond.
2.4 Subsequent Treatment
After cutting off the edge-cracked parts, perform accumulative roll-bonding (ARB) and intermediate annealing (e.g., holding at 800°C for 2 hours) to significantly improve the uniformity and strength of the sheet.
3. Auxiliary Processing Methods: Flexible Solutions for Special Requirements
3.1 Electroplating Method
Electroplate a copper layer on the surface of the molybdenum sheet to form a copper-clad molybdenum structure. This method is suitable for preparing ultra-thin molybdenum-copper composite materials, but the uniformity of the plating thickness must be strictly controlled.
3.2 Explosive Forming Method
Use the explosive shock wave to achieve instant bonding between the copper and molybdenum sheets, which is suitable for processing large-sized sheets. However, the equipment cost is high, and professional safety protection is required.
4. Key Processing Techniques: Details Determine Success
4.1 Temperature Control
Molybdenum-copper alloys are prone to oxidation above 600°C. Therefore, all heating processes should be carried out under vacuum or high-purity inert gas (such as argon) protection. The vacuum degree of the sintering furnace should be lower than 10⁻³ Pa.
4.2 Equipment Selection
For rolling, use a high-precision four-high rolling mill equipped with automatic roll gap control to ensure a thickness tolerance of ≤ ±0.01 mm. When performing wire electrical discharge machining (WEDM), use a special molybdenum-copper electrode wire and control the discharge energy to prevent cracks.
4.3 Parameter Optimization
When the total cold rolling deformation exceeds 50%, intermediate annealing must be carried out. The warm rolling temperature should be adjusted according to the sheet thickness (lower temperature for thin sheets and higher temperature for thick sheets).
4.4 Subsequent Treatment
After annealing, perform pickling (e.g., using a 10% hydrochloric acid solution) to remove the surface oxide layer, followed by polishing to improve the surface roughness to Ra ≤ 0.8 μm.
5. Application Case: Practice in the Electronic Packaging Field
A company used the powder metallurgy method to produce 0.2 mm thick molybdenum-copper thin sheets for the heat dissipation substrates of high-power electronic devices. By optimizing the sintering process (holding at 1350°C for 3 hours) and the cold rolling passes (a total of 4 passes with annealing after each pass), they successfully increased the thermal conductivity of the product to 220 W/(m·K) and controlled the flatness error within ±0.02 mm, meeting the requirements of high-end customers.
The processing of molybdenum-copper thin sheets requires a balance between material properties and process precision. By flexibly combining methods such as powder metallurgy and roll-bonding and strictly controlling key aspects such as temperature, equipment, and parameters, high-performance products can be stably produced. As electronic devices move towards miniaturization and high power, the processing technology of molybdenum-copper thin sheets will continue to innovate, providing stronger support for high-end manufacturing.