Galvanized Steel Sheet Welding: Technological Approach

Galvanized steel arc welding

The presence of zinc coating has brought some difficulties to the welding of galvanized steel. The main problems are:

  • The sensitivity of welding crack and stomata increased;
  • The evaporation and soot of zinc;
  • Oxide slag and zinc coating melt and destroy.

Among them, welding crack, stoma and slag are the main problems.

Galvanized Steel Sheet Welding

1.1  Weldability.

(1)The crack

During welding, molten zinc floats on the surface of the molten pool or at the root of the weld.

Since the melting point of zinc is much lower than that of iron, the iron in the molten pool will first crystallize, and the liquid zinc will infiltrate into it along the grain boundary of the steel, resulting in the weakening of the intercrystalline bond.

Moreover, the metal brittle compound Fe3Zn10 and FeZn10 are easily formed between zinc and iron, which further reduces the plasticity of weld metal.

Therefore, it is easy to crack along crystal boundary under the action of welding residual stress.


1) Factors affecting crack sensitivity

① Zinc thickness

The zinc coating of galvanized steel is thin and the crack sensitivity is small, while the zinc layer of hot galvanizing steel is thicker and the crack sensitivity is greater.

② The thickness of the workpiece

The greater the thickness, the greater the welding constraint stress and the crack sensitivity.

③ The groove clearance

The larger the gap, the more sensitive the crack.

④ Welding method

The crack sensitivity is small when welding with manual arc welding, and the crack sensitivity is much higher when welding with CO2 gas.


2) Methods to prevent cracks

① Before welding, open V, Y or X-shape groove at the welding place of galvanized sheet. Use oxyacetylene or sandblasting to remove the zinc coating near the groove, and the clearance should not be too large, generally 1.5mm.

② Choose welding materials with low Si content. In gas shielded welding, the welding wire with low Si content should be adopted. Titanium type and titanium calcium electrode are used for manual welding.



The zinc layer near the groove produces oxidation (ZnO) and vaporization under the action of arc heat, and it evaporates white smoke and vapor, so it is very easy to cause stomata in the weld.

The greater the welding current, the more serious the evaporation of zinc, the greater the stomatal sensitivity.

It is not easy to produce stomata in the medium current range when welding with titanium type and calcium titanium electrode.

When welding with cellulose type and low hydrogen welding electrode, both small current and large current are easy to produce stomata.

In addition, the electrode angle should be controlled in the range of 30-70°.

(3)The evaporation and soot of zinc

The zinc layer near the molten pool is oxidized into ZnO and evaporated by arc heat, forming a great dust.

The main component of this dust is ZnO, which has a great effect on workers’ respiratory organs.

Therefore, good ventilation must be taken in welding.

Under the same welding specification, the amount of dust produced when welding with titanium oxide electrode is low, while the amount of dust produced during welding of low hydrogen welding electrode is large.

(4)Oxide slag

When the welding current is small, the ZnO formed in the heating process is not easy to escape, easily form into ZnO slag.

ZnO is stable, its melting point is 1800 ℃.

The large block of ZnO slag has a very negative influence on the weld plasticity.

When using titanium oxide type electrode, ZnO shows a small uniform distribution, which has little effect on plasticity and tensile strength.

In the case of cellulose or hydrogen electrode, the ZnO in the welding seam is larger and more, and the weld performance is poor.

1.2  Welding process of galvanized steel.

Galvanized steel can be welded by manual electric arc welding, melting electrode gas shielded welding, argon arc welding, resistance welding, etc.

(1)Manual arc welding

1) Weld preparation

In order to reduce welding dust, prevent welding crack and stomatal formation, except to open the appropriate slope before welding, the zinc layer near the groove should be removed.

The removal method can be fired by flame or sandblast.

Groove clearance should be controlled within 1.5 ~ 2mm, and if the workpiece thickness is larger, the gap can be in the range of 2.5 ~ 3mm.


2) Selection of electrode

The selection principle of welding rod is that the mechanical properties of the weld metal are as close to the parent material as possible, and the amount of silicon in the welding electrode should be controlled below 0.2%.

The strength of the joints obtained by using ilmenite type electrode, titanium oxide type electrode, cellulose electrode, titanium calcium electrode and low hydrogen welding electrode can achieve satisfactory result.

However, slag and porosity are easily generated in welds when welded with low hydrogen electrode and cellulose electrode, so generally this method is not been adopted.

For mild steel galvanized steel sheet, J421/J422 or J423 welding rods should be preferred.

For galvanized steel plates with a strength level above 500MPa, E5001, E5003 welding rods should be used.

For galvanized steel plates with a strength of over 600MPa, the welding rods of E6013, E5503 and E5513 should be selected.

When welding, use short arc as far as possible, do not make the arc swing, to prevent the expansion of the melting zone of galvanized layer, ensure the corrosion resistance of the workpiece and reduce the amount of soot.


(2)Fusion electrode gas shielded welding

CO2 gas shielded welding or Ar+CO2, Ar+O2 mixed gas shielded welding should be adopted.

Protective gas has a significant effect on Zn content in the weld.

When pure CO2 or CO2+O2 is used, the content of Zn in the welding seam is high, while the content of Zn in the welding seam is low when Ar+CO2 or Ar+O2 is adopted.

The current has little effect on Zn content in the weld. As the welding current increases, the Zn content in the welding seam decreases slightly.

When welding galvanized steel with gas shielded welding, the welding dust is much bigger than the manual arc welding, so special attention should be paid to the exhaust.

The factors that affect the size and composition of soot are mainly current and protective gases.

The larger the current, or the greater the amount of CO2 or O2 in the gas, the greater the welding soot.

In addition, the content of ZnO in the soot also increases, and the maximum ZnO content can reach about 70%.

Under the same welding specification, the molten depth of galvanized steel is larger than that of non-galvanized steel.

The welding pores of T-joint, lap joint and down welding are more sensitive, and the larger the welding speed is, the more easily the pores will be generated.

The effect of welding speed is especially obvious for galvanized alloy steel.

In multi-line welding, the stomatal sensitivity of subsequent welding lines is greater than that of the previous one.

The protective gas composition has no great influence on the mechanical properties of the joints, and the pure CO2 is generally used for welding.

The welding parameters of CO2 welding for the I-shaped butt joint, lap joint and T-joint of galvanized steel plate are given respectively on following table 1-3.

Table 1 Specification parameters for CO2 welding of I-shaped galvanized steel plate butt joint.

Thickness/mmGap/mmWelding PositionWire Feed Speed/mm*s-1Arc voltage/VWelding Current/AWelding Speed/mm*s-1Note
1.60Flat Welding59.2~80.417~2070~905.1~7.2Welding wire ER705-3

Dia. 0.9mm

Dry extension 6.4mm

Vertical Down Welding82.517905.9
Horizontal Welding50.8181008.5
Overhead Welding50.8~5518~19100~110
3.20.8~1.5Flat Welding71.9201355.5
Vertical Welding71.9201357.6
Horizontal Welding71.9201356.8
Overhead Welding71.9201355.5

Table 2 Specification parameters for CO2 welding of galvanized steel plate lap joint.

Thickness/mmWelding PositionWire Feed Speed/mm*s-1Arc voltage/VWelding Current/AWelding Speed/mm*s-1Note
1.6Flat Welding50.8191105.1~6.8Welding wireER705-3

Dia. 0.9mm

Dry extension6.4mm

Horizontal Welding50.819~20100~1105.5~6.8
Overhead Welding50.819~20100~1104.2~5.1
Vertical Welding50.8181005.5~6.8
3.2Flat Welding67.2191353.8~4.2
Horizontal Welding67.2191353.8~4.2
Vertical Down Welding67.7191355.1
Overhead Welding59.2191353.4~3.8

Table 3 Specification parameters for CO2 welding of T-shaped galvanized steel plate butt joint (angle joint).

Thickness/mmWelding PositionWire Feed Speed/mm*s-1Arc voltage/VWelding Current/AWelding Speed/mm*s-1Note
1.6Flat Welding50.8~5518100~110Welding wireER705-3

Dia. 0.9mm

Dry extension6.4mm

Vertical Welding55~65.619110~120
Overhead Welding5519~201105.9
Horizontal Welding59.2201205.1
3.2Flat Welding71.9201354.7
Vertical Welding71.9201355.9
Horizontal Welding71.9201354.2
Overhead Welding71.9201355.1


2018-03-04T22:00:25+00:00 Welding|

Leave A Comment

error: Content is protected !!
Free blog updates delivered to your inbox?