Flux is a chemical material used in welding processes to clean and protect welding surfaces. It plays a crucial role in welding, enhancing the quality and efficiency of welds. This article provides a detailed introduction to the definition, classification, composition, performance, selection principles, and application fields of flux.

I. Definition of Flux

Flux is a chemical substance used during welding to remove oxides and impurities from the metal surfaces, prevent oxidation during welding, and promote the flow and wettability of the filler metal. The use of flux can significantly improve welding quality and reduce welding defects.

II. Classification of Flux

1. Classification by Chemical Composition

  • Rosin-Based Flux: Made from rosin and solvents, suitable for electronic welding with good insulation properties and low corrosiveness.
  • Non-Rosin-Based Flux: Does not contain rosin, primarily composed of organic acids and activators, suitable for welding where high insulation is not required.
  • Acid Flux: Contains strong acids with high deoxidizing capability, suitable for welding difficult metals but highly corrosive and requiring thorough cleaning.
  • Neutral Flux: Contains neutral substances, non-corrosive to metals, suitable for general welding.
  • Alkaline Flux: Contains alkaline components, used for welding specific metals with some deoxidizing capability.

2. Classification by Form

  • Liquid Flux: Exists in liquid form, easy to apply and immerse, widely used in electronic welding and wave soldering.
  • Solid Flux: Exists in solid form, such as solder paste and flux-cored rods, suitable for manual and automated welding.
  • Gaseous Flux: Exists in gas form, typically used in specific welding processes like hydrogen brazing.

3. Classification by Application Field

  • Electronic Flux: Specifically for welding electronic components, requiring good insulation properties and minimal residue.
  • Industrial Flux: Used for industrial welding, suitable for large-scale metal structures with strong deoxidizing capabilities.
  • Specialty Flux: Used for specific materials and special welding processes, such as welding aluminum, magnesium, and other difficult metals.

III. Composition of Flux

Flux typically includes the following components:

1. Activators

Activators are the main components of flux, responsible for removing oxides and impurities from the metal surfaces. Common activators include organic acids, inorganic acids, and fluorides.

2. Solvents

Solvents dissolve and dilute other components in the flux, making it easier to apply and flow. Common solvents include alcohol, water, and organic solvents.

3. Rosin

Rosin is a natural resin commonly used in electronic flux, providing good insulation properties and low corrosiveness.

4. Additives

Additives improve the performance of flux, including wetting agents, preservatives, and stabilizers.

IV. Performance of Flux

1. Deoxidizing Ability

Deoxidizing ability is one of the most critical properties of flux, determining its efficiency in removing oxides from metal surfaces during welding. A flux with strong deoxidizing ability can effectively clean metal surfaces, ensuring welding quality.

2. Wettability

Wettability refers to the ability of flux to make the filler metal spread uniformly on the metal surface. Good wettability can enhance weld strength and reduce defects.

3. Residue

Flux leaves residue on the weld seam surface after welding. The nature of the residue directly affects post-weld treatment and performance. Ideally, flux residues should be low in corrosiveness and easy to clean.

4. Insulation Properties

Insulation properties are crucial for electronic welding. A flux with good insulation properties prevents short circuits or leakage after welding.

V. Principles for Selecting Flux

1. Selection Based on Welding Material

Different materials require corresponding fluxes. For instance, welding aluminum requires specialized aluminum flux.

2. Selection Based on Welding Method

Different welding methods have varying requirements for flux. For example, wave soldering and manual welding may need different types of flux.

3. Selection Based on Welding Environment

The welding environment, including temperature, humidity, and contamination levels, should dictate the choice of flux. For instance, high-temperature environments require high-temperature resistant flux.

4. Selection Based on Welding Quality Requirements

Flux should be selected based on the quality requirements of the weld, including weld strength, surface finish, and residue characteristics. For high-precision electronic components, flux with minimal residue and good insulation properties should be chosen.

VI. Application Fields of Flux

1. Electronics Industry

Flux is widely used in the electronics industry for soldering printed circuit boards (PCBs), electronic components, and microelectronic devices, requiring good insulation properties and low corrosiveness.

2. Automotive Industry

In the automotive industry, flux is used for welding body panels, chassis, and engine parts, requiring strong deoxidizing capabilities and good wettability to ensure weld strength and durability.

3. Aerospace Industry

The aerospace industry demands extremely high welding quality. Flux is used for welding high-precision parts of aircraft, spacecraft, and missiles, requiring minimal residue and excellent insulation properties.

4. Construction and Mechanical Engineering

In construction and mechanical engineering, flux is used for welding steel structures, pipelines, and machinery, requiring strong deoxidizing capabilities and good wettability to ensure welding quality and structural strength.

5. Power Industry

Flux in the power industry is used for welding electrical equipment and transmission lines, requiring good conductivity and corrosion resistance to ensure the stable operation of power systems.


As a crucial chemical material in welding processes, flux comes in various types and has wide-ranging applications. Understanding the definition, classification, composition, performance, selection principles, and application fields of flux is essential for improving welding quality and efficiency. With technological advancements, the materials and formulations of flux continue to innovate, providing better solutions for the welding needs of various industries.

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