(1) When the line expansion coefficient of the two welded metals is very different, in the welding process will produce a lot of thermal stress, and this stress can not be eliminated, will eventually lead to the welding structure under the action of thermal stress damage.
(2) When the melting temperature of the two welded metal joints varies greatly, one of the metals is already in a melting state during the welding process, while the other metal is still under solid state. Therefore, the greater the melting point of heterogeneous metal hoses, the more difficult to weld.
(3) The greater the difference between the thermal conductivity and the specific heat capacity of the two metals, the more difficult it is to weld. Because the greater the difference between the thermal conductivity and the specific heat capacity, the crystallization conditions of the weld will become worse, and the grain roughness of the weld is serious.
(4) When the oxidation of the two welded metals is stronger, the more difficult it is to weld. Because, in the welding process, there are for particles in the grain boundary, which will reduce the bonding force between the crystals, so that the weld can produce slag and cracks.
