Are you interested in learning about the challenges and solutions for welding brass? Brass, a copper-zinc alloy, is notoriously difficult to weld due to the low boiling point of zinc, which causes evaporation and oxidation during the welding process.
However, with the use of silicon-containing welding wire and proper welding methods such as stick arc welding and argon arc welding, the weldability of brass can be improved.
In this article, we will delve into the details of brass welding, including key process points, welding parameters, and post-welding treatments. Whether you are a welder or simply curious about the science behind welding, this article is a must-read!
1. Weldability of brass
Brass is a copper-zinc alloy, and due to the low boiling point of zinc (only 907℃), it is very easy to evaporate during the welding process, which is the biggest problem in brass welding.
Under high-temperature conditions during arc welding with brass welding rod, the amount of zinc evaporation can be as high as 40%, which leads to a decrease in the mechanical and corrosion resistance properties of the welded joint, and increases its sensitivity to stress corrosion.
The evaporated zinc is immediately oxidized into zinc oxide in the air, forming white smoke, which brings great difficulties to the operation and affects the welder’s health.
Therefore, when welding brass, it is necessary to strengthen ventilation and other protective measures.
Poor weldability of brass can cause problems such as porosity, cracks, zinc evaporation, and oxidation during welding.
To solve these problems, silicon-containing welding wire is commonly used in welding, because silicon will form a dense oxide film on the surface of the molten pool, blocking the evaporation and oxidation of zinc, and preventing hydrogen from invading.
After welding, annealing at 470-560℃ can be carried out to eliminate stress and prevent the phenomenon of “self-cracking.
2. Welding methods for brass
The commonly used welding methods for brass in production are stick arc welding and argon arc welding, and their key process points are as follows:
(1) Stick arc welding: Brass welding rod with bronze core wire is used, such as ECuSn-B (T227), ECuAl-C (T237). Pure copper core wire such as ECu (T107) can be used for brass castings that do not require high welding requirements.
The power supply should be DC positive connection, and the V-shaped groove angle should not be less than 60°-70°.
When the plate thickness exceeds 14mm, the surface of the weldment should be carefully cleaned before welding to remove all oil impurities that will generate hydrogen gas.
Short arc welding should be used during operation, and the welding rod should not be swung horizontally or longitudinally, only moving along the straight line of the weld. The welding speed should be fast, not less than 0.2-0.3m/min.
When multi-layer welding, the oxide film and slag between the layers should be removed. The copper liquid of brass has high fluidity, so the molten pool should be in a horizontal position. If the molten pool must be tilted, the inclination angle should not be greater than 15°.
(2) Argon arc welding: Tin-brass welding wire HSCuZ-1 (HS221), iron-brass welding wire HSCuZn-2 (HS222), and silicon-brass welding wire HSCuZn-4 (HS224) are used in manual tungsten argon arc welding.
These welding wires contain high zinc content and produce large smoke during welding. Bronze welding wire such as HSCuSi (HS211) and HSCuSn (HS212) can also be used.
The welding parameters for manual tungsten argon arc welding of brass are shown in the table.
|Material Science||Plate thickness/mm||Groove form||Tungsten electrode diameter/mm||Type and polarity of power supply||Welding current/||Argon gas flow rate A/(L/min)||Preheating temperature/℃|
|Ordinary brass||1.2||Termination||3.2||DC direct connection||185||7||Not preheating|
|Tin brass||2||V-shaped||3.2||DC direct connection||180||7||Not preheating|
Due to the evaporation of zinc, which destroys the protective effect of argon gas, a larger nozzle aperture and argon gas flow rate should be selected when welding brass.
Generally, preheating is not required before welding, except for joints with a thickness greater than 10mm and joints with a significant difference in thickness between the welding edges, in which case only the thicker part of the weldment edge needs to be preheated.
The power supply can use DC positive connection or AC. When using an AC power supply for welding, the amount of zinc evaporation is relatively small.
Larger welding current and faster welding speed should be used for welding parameters.
The welding parameters for welding 16-20mm thick brass plates are: welding current of 260-300A, tungsten electrode diameter of 5mm, welding wire diameter of 3.5-4.0mm, nozzle aperture of 14-16mm, and argon gas flow rate of 20-25L/min.
To reduce the evaporation of zinc, the filling wire can be “short-circuited” with the workpiece during operation, and the arc can be initiated and maintained on the filling wire as much as possible, avoiding direct arc contact with the base metal. The base metal is mainly heated and melted by the heat transfer of the molten pool metal.
During welding, single-layer welding should be carried out as much as possible. For joints with a thickness less than 5mm, it is best to weld them in one pass.
After welding, the weldment should be heated to 300-400℃ for annealing to eliminate welding stress and prevent the brass component from cracking during use.