The quality of the welding also depends on the base material and filler material used. Not all metals can be welded, and different base materials need to be paired with specific fluxes.
Iron The weldability of different steel materials is inversely proportional to their own hardening characteristics, which refers to the ability of the steel to produce martensite during cooling. The hardening properties of steel depend on its chemical composition, and if a steel material contains a higher proportion of carbon and other alloying elements, its hardening characteristics are higher, and therefore solderability is relatively low. To compare the solderability of different alloy steels, a method called equivalent carbon content can be used, which can reflect the weldability of different alloy steels relative to ordinary carbon steels. For example, the effect of chromium and vanadium on solderability is higher than that of copper and nickel, and the above alloying elements have a smaller influence factor than carbon. The higher the equivalent carbon content of alloy steel, the lower the weldability. If ordinary carbon steel and low alloy steels are used for high solderability, the strength of the product is relatively low-there is a delicate trade-off between solderability and product strength.
The high-strength low-alloy steels that were opened in the 1970 overcame the contradiction between strength and solderability, which had high strength and good solderability, making them an ideal material for welding applications. Because the stainless steel contains a higher proportion of chromium, so the analysis of its weldability is different from other steel. Austenite in stainless steels has good solderability, but austenite is sensitive to distortion due to its high coefficient of thermal expansion. Some austenitic stainless steels are prone to breakage, thus reducing their corrosion resistance. If you do not pay attention to control the formation of ferrite during welding, it may lead to thermal fracture. To solve this problem, an additional electrode head can be used to deposit a weld metal containing a small amount of ferrite.
Ferritic stainless steel and martensitic stainless steel weldability is also not good, in the welding must be preheated, and welding with special welding electrodes.
Aluminum The solderability of aluminum alloys varies greatly with the alloying elements. The sensitivity of aluminum alloy to thermal fracture is very high, so the method of high welding speed and low heat input is usually used in welding. Preheating can reduce the temperature gradient in the weld area, thus reducing thermal fracture. However, Preheating also reduces the mechanical properties of the base material and cannot be applied when the base material is fixed. The use of suitable joint form and better compatibility of the filler alloy can reduce the emergence of thermal fracture. Aluminum alloys should clean the surface before soldering, removing oxides, oil and loose impurities.
Surface cleaning is very important, because aluminum alloy welding, too much hydrogen will cause foam, excessive oxygen will form scum