Optimization measures for vacuum brazing of aluminum alloy water-cooled radiator

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Aluminum alloy water-cooled radiators are increasingly widely used in heat dissipation fields such as rail transportation, aerospace, ships, and wind power due to their high efficiency in heat dissipation, green and safe characteristics.

Vacuum brazing does not require the addition of brazing flux during brazing, and multiple radiators can be brazed at one time. It is especially suitable for the welding and forming of radiators with complex flow channels. Therefore, vacuum brazing is increasingly widely used in water-cooled radiators.

Vacuum brazing refers to a welding technology in which the parts to be welded and the brazing material are locked in a fixture under a certain vacuum degree, and the temperature is higher than the liquidus line of the brazing material and lower than the solidus line of the parent material. The liquid brazing material fills the gap between the parts to be welded under the capillary force, and the brazing material solidifies when the temperature drops to connect the parts to be welded.

At present, the defects of vacuum brazing of aluminum alloy water-cooled radiators and their control measures are as follows:

1.Porosity

Causes: Improper selection of brazing material (containing low-boiling-point elements), incomplete cleaning of the parent material or brazing material, and insufficient vacuum degree, resulting in the inability of crystal water or oil to escape.

Performance: Circular holes are formed on the surface or inside of the weld.

Optimization measures for vacuum brazing: Select brazing materials that do not contain low-boiling-point elements; thoroughly clean the base material and brazing materials, and dry to remove moisture; ensure that the vacuum degree is lower than (1×10^-3Pa) (before reaching the solidus of the brazing material).

2.Flowing

Cause: The brazing temperature is too high/the holding time is too long, the amount of base material dissolved is too large, the brazing gap is too large, and the heat capacity of the tooling is large.

Performance: The liquid brazing material overflows the brazing surface, affecting the surface flatness.

Optimization measures for vacuum brazing: Optimize the brazing temperature-time curve, reduce the amount of furnace loading and the heat capacity of the tooling; control the brazing gap (adjusted by flatness and clamping torque); mechanically remove existing flow defects.

3.Erosion

Cause: The interaction between the brazing material and the base material is too strong, the amount of brazing material is too much, the temperature is too high/the holding time is too long.

Performance: Pits appear on the surface of the base material.

Optimization measures for vacuum brazing: Select appropriate brazing material with low liquidus; reduce brazing material thickness (from 0.2mm to 0.1mm); use fusion welding to repair defective areas.

4.Cracks

Causes: Excessive clamping torque leads to separation, too fast heating/cooling rate leads to thermal stress, and brittle phase of brazing material is generated.

Performance: Cracks appear in the brazing seam.

Optimization measures for vacuum brazing: Adjust the clamping torque to an appropriate value; slow down the heating/cooling rate (increase the insulation section); select high-plasticity brazing material.

5.Brazing bulge

Causes: Segregation of parent material components (aggregation in low melting point areas), too high brazing temperature.

Performance: Tumor-like protrusions form on the surface of the radiator.

Optimization measures for vacuum brazing: Strengthen material composition detection to avoid segregation; reduce brazing temperature or shorten insulation time; slight bulges can be removed by machining. 6. Poor welding

Reasons: Incomplete cleaning, unreasonable temperature curve, excessive ambient humidity, insufficient vacuum, poor flatness/roughness.

Performance: Low brazing rate or penetration defects.

Vacuum brazing optimization measures: Control ambient humidity≤60%; Ensure the roughness of the substrate/cover plate (Ra≤3.2 u m); The liquidus temperature of the brazing material is higher than the solidus temperature of the parent material.

6.Leakage

Reasons: Poor welding causes penetration defects, unreasonable structural design (such as the positioning hole is too close to the flow channel), and insufficient strength of the substrate/cover plate.

Performance: Gas/liquid leakage during airtight test or operation.

Vacuum brazing optimization measures: Increase the distance between the positioning hole/threaded hole and the flow channel; Reduce the area of the flow channel confluence to improve the pressure bearing capacity; Optimize the thickness design of the substrate/cover plate.

7.Misalignment

Reasons: Imprecise assembly, insufficient clamping force of the tooling, and poor horizontality of the furnace body.

Performance: Relative displacement between the substrate and the cover plate.

Optimization measures for vacuum brazing: use locating pins during assembly; increase tooling clamping force; reprocess the cover plate after repair welding.

8.Deformation

Cause: too fast heating/cooling rate leads to temperature gradient, insufficient tooling rigidity, and uneven clamping force.

Performance: overall or partial deformation of the radiator.

Optimization measures for vacuum brazing: optimize heating/cooling process (segmented insulation); select high-strength tooling materials; cool to below 50°C before removing the fixture.

9.Flow channel blockage

Cause: too much brazing material, too narrow flow channel design, and too high brazing temperature lead to increased dissolution of the parent material.

Performance: liquid brazing material accumulates and solidifies in the flow channel.

Optimization measures for vacuum brazing: reduce the amount of brazing material used (cut brazing sheet); widen/increase the flow channel design; use vacuum diffusion welding for micro-flow channel structure.

Vacuum brazing operation suggestions

Optimization of vacuum brazing process parameters: vacuum degree, temperature curve, and heating rate need to be dynamically adjusted according to the furnace load;

Material and design optimization: Prioritize the use of base materials with uniform composition (such as 4-series aluminum-silicon-magnesium brazing filler metals) to avoid structural designs with high defect sensitivity;

Environmental control: The humidity of the production environment needs to be strictly managed, and the cleaning process needs to be standardized.

After the implementation of the above measures, the defect rate can be significantly reduced, and the quality of the finished product can be further improved by combining process monitoring (such as water immersion ultrasonic testing).

Vacuum Brazing Furnace