Brazing vs. Welding: Key Differences Explained

I. Fundamental Principles (See Figure 1)

Welding

Atomic-Level Fusion

Mechanism: Base material melts and recombines.

Temperature: Molten pool > base material melting point (e.g., steel: 1,600°C+).

Bond Type: Continuous grain growth.

Brazing

Metallurgical Bonding

Mechanism: Capillary action with filler material.

Temperature: 30-50°C above filler’s liquidus (e.g., copper-based filler: 900°C).

Bond Type: Diffusion layer formation (3-10μm thick).

II. Process Comparison

Parameter	Welding	Brazing
Heat Input	Concentrated (arc/laser)	Uniform (furnace/induction)
Base Material	Localized melting	Remains solid
Deformation	Fixtures required (1-3mm distortion)	Free-state (<0.2mm distortion)
Joint Gap	0-2mm (self-fusing)	0.05-0.2mm (capillary flow)

III. Material Compatibility
Dissimilar Materials:

Welding: Requires metallurgical compatibility (e.g., steel-nickel).

Brazing: Bonds ceramics to metals.

Thin/Thick Combinations:

Welding: Preferable for thick plates (20mm penetration).

Brazing: Ideal for thin foils (0.1mm).

IV. Strength Performance

Static Strength:

Welded joints: 90-110% of base material.

Silver-brazed joints: 60-80% of base material.

Fatigue Resistance:

Welding: HAZ reduces lifespan by 30-50%.

Brazing: Homogeneous joints improve cycles by 2-3x.

V. Applications

Welding                                                     Brazing

✓ Structural steel (beams)             ✓ Electronics (heat sinks)

✓ Pressure vessels                        ✓ Aerospace (honeycomb panels)

✓ Shipbuilding (deck joints)         ✓ Sensors (precision assemblies)

VI. Selection Guide

Primary Criteria:

Material thickness >3mm → Choose welding.

Precision <0.1mm → Choose brazing.

Secondary Factors:

Heat-sensitive parts: Brazing.

Dynamic loads: Welding.

Dissimilar materials: Brazing.

VII. Quality Control

Welding

Penetration testing (UT inspection).

HAZ hardness: HV300-350.

Residual stress (X-ray diffraction).

Brazing

Wetting angle: θ <15°.

Gap fill rate: >95%.

Intermetallic layer: <5μm.

Advanced Insight:

Modern braze-cladding hybrid processes (e.g., nuclear component repairs) achieve base-material-strength joints at <500°C, revolutionizing traditional limits.