Acidic vs Alkaline Electrodes: How to Distinguish Them with Expert Guidance

Welding rod

The most common electrodes are J422 and J507, where J422 is an acidic electrode and J507 is an alkaline electrode.

Based on the alkalinity classification of the slag produced after welding, welding rods can be divided into acidic welding rods and alkaline welding rods.

Related reading: How to Choose the Right Welding Rod?

How to distinguish acid electrode from alkaline electrode more quickly?

The welding rod grade can reveal whether the welding rod is being used with a DC welding machine or an AC welding machine. Additionally, the welding rod grade can also indicate whether the welding rod is acidic or alkaline.

The J422 series of welding rods includes J421, J422, J423, J424, J425, J426, and J427. The J507 series of welding rods includes J501, J502, J503, J504, J505, J506, and J507. These are all part of the carbon steel series of welding rods.

To understand the specific meaning of a welding rod grade, look at the last digit of the grade. The last digit indicates the specific meaning.

The third digit of the grade also indicates the type of coating on the electrode. Electrodes with a high amount of acidic oxides (such as TiO2 and SiO2) in their coating are referred to as acidic electrodes.

This includes electrodes with titanium oxide type coating, titanium calcium type coating, ilmenite type coating, iron oxide type coating, and high cellulose type coating. These are acidic electrodes, indicated by third digit numbers 1, 2, 3, 4, and 5. They can be used with both AC and DC welding machines.

Acidic electrodes offer good welding process performance, with a stable arc and minimal spatter, as well as good slag fluidity and easy deslagging, leading to a beautiful weld appearance.

However, due to the high presence of silicate, iron oxide, titanium oxide, etc. in the coating, oxidation is strong, but the mechanical properties of the weld, particularly its impact toughness, are poor. It is therefore best suited for welding general low carbon steel and low alloy structural steel with low strength. It is the most commonly used type of electrode.

Alkaline electrodes have a high amount of alkaline oxides (such as CaO and Na₂O) in their coating. They rely on the decomposition of CO₂ from carbonates (such as CaCO₃ in marble) as the protective gas, and the combination of CaF₂ in fluorite with H to synthesize hydrogen fluoride (HF) at high temperatures, which reduces the hydrogen content in the weld. Thus, alkaline electrodes are also known as low hydrogen electrodes.

The electrodes with low hydrogen potassium (J506) and low hydrogen sodium (J507) coatings are classified as alkaline electrodes and are rated as 5 and 6 in terms of electrode quality.

The J506 coating contains an arc stabilizer, which makes it easier to start an arc and maintain a stable arc during welding. This allows the J506 electrode to be used for both AC and DC welding, whereas the J507 electrode can only be used for DC welding with reverse polarity.

Comparison of characteristics of acid electrode and alkaline electrode:

• The components of the coating of acid electrodes have strong oxidizing properties, while the components of the coating of alkaline electrodes have weak oxidizing properties.
• Acid electrodes are not sensitive to porosity caused by water and rust, and must be baked at temperatures between 75-150 ℃ for 1 hour before use. On the other hand, alkaline electrodes are sensitive to porosity caused by water and rust, and must be baked at temperatures between 350-400 ℃ for 1-2 hours before use.
• The arc of acid electrodes is stable and can be used for both AC and DC welding. However, alkaline electrodes, which contain fluoride in their coating that deteriorates the stability of the arc, must be welded with DC. Only when an arc stabilizer is added to the coating, can the electrode be used for both AC and DC welding.
• The welding current of acid electrodes is high, while the welding current of alkaline electrodes is about 10% smaller than that of acid electrodes of the same specifications.
• Acid electrodes should be operated with a long arc, while alkaline electrodes should be operated with a short arc to prevent the formation of porosity.
• The transition effect of alloy elements in acid electrodes is poor, while the alkaline electrode has a good transition effect of alloy elements.
• The welds produced by acid electrodes are well-formed and have shallow penetration, while the welds produced by alkaline electrodes have good formation, are easy to build up, and have slightly deeper penetration.
• The slag structure of acid electrodes is glassy, while the slag structure of alkaline electrodes is crystalline.
• It is easy to remove slag from acid electrode welds, but the first layer in the groove of alkaline electrode welds is difficult to remove, while subsequent layers are easy to remove.
• The impact performance of acid electrode welds at normal and low temperatures is generally poor, while the impact performance of alkaline electrode welds at normal and low temperatures is high.
• Acid electrodes have poor crack resistance, while alkaline electrodes have good crack resistance.
• The hydrogen content in the welds produced by acid electrodes is high and can easily lead to the formation of “white spots” and affect plasticity, while the hydrogen content in the welds produced by alkaline electrodes is low.
• There is less smoke and dust during acid electrode welding, while there is more smoke and dust during alkaline electrode welding.

Comparison table of differences between acid electrode and alkaline electrode