Welding Wire problems in the welding process
First, strong oxidation capacity
The affinity of aluminum and oxygen is very strong in the air and easily combined with oxygen to produce dense and strong AL2O3 film, the thickness of about 0.1μm, the melting point of up to 2050 ℃, far more than the melting Wire melting point, and the density is large, about 1.4 times the aluminum. In the welding process, the alumina film will hinder the good combination between the metal, and easily lead to slag. The oxide film will absorb moisture, welding will cause the weld to generate pores. These defects, will reduce the performance of welded joints. In order to ensure the quality of the welding, it is necessary to strictly clean the surface of the weldment before welding, and to prevent re-oxidation during the welding process, the metal and metal in the high temperature of the effective protection, which is welding Wire welding an important feature. The specific protection measures are: 1, before welding with mechanical or chemical methods to remove the workpiece groove and the surrounding parts and wire surface oxide; 2, the welding process to use qualified protective gas protection; 3, in the gas welding, the use of Flux, in the welding process continue to use the wire to break the surface of the molten film melting film.
Second, the thermal conductivity of aluminum and specific heat, thermal fast
Although the melting wire has a much lower melting point than steel, the thermal conductivity of the Welding Wire is much larger than the heat capacity, more than double the steel, and a lot of heat is quickly transferred to the base metal during the welding process. In order to obtain high quality welding Joints, must use energy concentration, power of the heat source, and sometimes need to use preheating and other technical measures to achieve the welding process.
Third, the linear expansion coefficient
Welding Wire's linear expansion coefficient is about 2 times the steel, solidification when the volume shrinkage of 6.5% -6.6%, so easy to produce welding deformation. Effective measures to prevent deformation are in addition to the selection of reasonable process parameters and welding sequence, the use of suitable welding tooling is also very important, especially when welding thin sheet. In addition, the tendency to form crystal cracks in the weld metal and the tendency to form liquefied cracking in the heat affected zone are high due to certain weld wire welding, and heat is often generated in the brittle temperature range due to excessive internal stress crack. This is one of the most common serious defects in Welding Wire, especially high strength solder wire welding. In the actual welding site to prevent such cracks in the main measures to improve the joint design, select a reasonable welding process parameters and welding sequence, using the characteristics of the base metal to adapt to the welding filler.
Four, easy to form pores
The stomata in the welded joint is a defect that is easily generated when welding Wire is welded, especially for pure aluminum and rust-proof aluminum. Hydrogen is the main cause of the formation of pores during weld Wire welding, as evidenced by practice. The source of hydrogen, mainly in the arc column atmosphere of moisture, welding materials and base metal adsorption of water, which wire and base metal surface oxide film adsorption of water to weld the stomatal production, often occupies a prominent position.
Welding Wire's liquid pool is easy to absorb gas, a large amount of gas dissolved in the high temperature, in the liquid solidification, the sharp decline in solubility, cooling and solidification in the process of cooling after the precipitation, and gathered in the weld to form pores. In order to prevent the generation of stomata in order to obtain a good welded joint, the source of hydrogen should be strictly controlled, before welding must be strictly limited use of welding materials (including welding wire, welding rod, flux, shielding gas) water content, before use Drying treatment. After cleaning the base metal and welding wire is best in 2-3 hours welding completed, up to no more than 24 hours. TIG welding, the choice of large welding current with a higher welding speed. MIG welding, the choice of large welding current slow welding speed, in order to improve the existence of molten pool time. Al-Li alloy welding, strengthen the front and back protection, with the groove scraping, clear the oxide film, can effectively prevent the pores.