Why is it necessary to process the surface of the base material before welding?

Pre-weld surface treatment of the base metal removes impurities such as oil, paint, rust, mill scale, and moisture to prevent them from melting into the weld and causing defects such as porosity, slag inclusions, and cracks. This ensures weld quality, reduces rework, and increases the life of the workpiece. Surface treatment also reduces thermal stress in the weld area, prevents deformation and cracking, and enhances the surface metal's luster.
Why is pre-weld surface treatment necessary?
1. Remove impurities and prevent weld defects
During the welding process, impurities such as oil, paint, rust, mill scale, and moisture can melt into the weld, causing defects such as porosity, slag inclusions, and cracks, seriously affecting the strength and quality of the weld.
2. Ensure the chemical composition and physical properties of the weld
Impurities can alter the chemical composition of the weld, affecting its metallurgical structure and mechanical properties, leading to reduced weld performance.
3. Reduce stress and improve deformation resistance
Preheating the base metal removes some moisture and reduces the temperature difference between the weld zone and the cold base metal. This reduces high thermal stress caused by uneven heating and cooling, thereby reducing weld deformation and residual stress.
4. Improve surface condition and weldability
Surfaces with a metallic sheen are more easily melted and fused by the arc, improving welding efficiency and success rate.
Common Surface Treatment Methods
1. Mechanical Cleaning
Use mechanical tools such as wire brushes and grinders to remove surface oil, rust, and scale.
2. Chemical Cleaning
For materials prone to forming oxide layers, such as aluminum, a specialized solvent can be used to remove the surface oxide layer.
3. Preheating
Heat the workpiece surface to a certain temperature before welding to remove moisture and reduce thermal stress.
Mjere predostrožnosti
When welding stainless steel, a stainless steel wire brush must be used to prevent residual iron filings from becoming impurities and causing rust.
When cleaning aluminum, avoid using chlorine-containing solvents to prevent the production of toxic gases.