In addition to differences in alloy composition, dissimilar metal hoses also have differences in metallurgy, physics, chemistry and welding processes. Some dissimilar metal hoses are quite different, so welding dissimilar metal hoses is usually much more difficult than welding the same metal. The main problems of dissimilar metal hose welding are as follows:
(1) When the linear expansion coefficients of the two metals to be welded are very different, a large thermal stress will be generated during the welding process, and this stress cannot be eliminated, which will eventually lead to the welding structure under the action of thermal stress. destroy.
(2) When the melting temperatures of the two metal joints to be welded differ greatly, during the welding process, one of the metals is already in a molten state while the other is still in a solid state. Therefore, the greater the difference in melting points of dissimilar metal hoses, the more difficult it is to weld.
(3) The greater the difference in thermal conductivity and specific heat capacity of the two metals, the more difficult it is to weld. Because the greater the difference between thermal conductivity and specific heat capacity, the crystallization condition of the weld will deteriorate, and the grain coarsening of the weld will be serious.
(4) The stronger the oxidation of the two metals to be welded, the more difficult it is to weld. Because, during the welding process, the oxides existing in the grain boundaries will reduce the bonding force between the grains, causing slag inclusions and cracks in the weld.
(5) Due to the high brittleness of intermetallic compounds, it is easy to cause cracks or even fractures in the weld. Therefore, the more intermetallic compounds are formed between the two metals to be welded, the more difficult it is to weld.
(6) During the welding process, because the metal elements with low melting point are easy to burn and evaporate, the chemical composition of the weld metal changes and the mechanical properties decrease. Therefore, when welding dissimilar metal hoses, the weld and the two base metals are not easy to achieve equal strength.
(7) When two metals are welded, the greater the difference in electromagnetic properties, the more unstable the welding arc and the worse the weld formation will be. Therefore, the greater the difference in electromagnetic properties of dissimilar metal hoses, the more difficult it is to weld.
(8) The greater the difference in chemical composition of dissimilar metal hoses, the more difficult it is to achieve high-quality welded joints, that is, the poorer the weldability.