Welding dissimilar metals is a common practice in many industries, such as construction, oil and gas, automotive, and aerospace. It allows combining different metal properties, such as strength, corrosion resistance, and ductility, to achieve a lower material cost and a better performance. However, welding dissimilar metals also poses some challenges, such as poor bonding, cracking, or material failure, if not done properly.
One of the key factors to consider when welding dissimilar metals is the selection of the filler metal, which is the material that melts and flows between the two base metals to create a weld joint. The filler metal should be compatible with both base metals, and provide the desired weld characteristics and service requirements. In this article, Megmeet Welding will explain how to choose the right filler metal for welding dissimilar metals, and what are the advantages and disadvantages of some common filler metals.
I. Factors to Consider When Choosing a Filler Metal
When selecting a filler metal for welding dissimilar metals, there are several factors to consider, such as:
1) Base metals:
The base metals are the materials that are being welded together. They may have different chemical compositions, mechanical properties, and thermal expansion coefficients, which can affect the weldability and the weld performance. The filler metal should match or exceed the strength of the weaker base metal, and have a similar or intermediate coefficient of thermal expansion to avoid cracking due to thermal stresses. The filler metal should also have a similar or lower melting point than the base metals, to avoid overheating or burning through the base metals.
2) Welding position:
The welding position is the orientation of the weld joint relative to the horizontal plane. It can be flat, horizontal, vertical, or overhead. The welding position can affect the fluidity and the solidification of the filler metal, and thus the weld quality and appearance. The filler metal should be suitable for the welding position, and have a low or moderate fluidity to avoid sagging or dripping in vertical or overhead positions. The filler metal should also have a fast or moderate solidification rate to avoid porosity or cracking in the weld.
3) Shielding gas:
The shielding gas is the gas that surrounds the arc and the weld pool during the welding process. It protects the weld from atmospheric contamination, such as oxygen, nitrogen, and moisture, which can cause oxidation, embrittlement, or porosity in the weld. The shielding gas can also influence the arc stability, the penetration, and the cleaning action of the weld. The filler metal should be compatible with the shielding gas, and have good arc stability and a sufficient penetration and cleaning action with the chosen gas. The shielding gas can be inert, such as argon or helium, or active, such as carbon dioxide, or mixtures of argon and carbon dioxide.
4) Design requirements:
The design requirements are the specifications and codes that define the expected performance and service conditions of the weld. They may include factors such as corrosion resistance, impact resistance, fatigue resistance, hardness, ductility, and appearance. The filler metal should meet or exceed the design requirements, and have the appropriate chemical composition, mechanical properties, and metallurgical structure to resist the service environment and the loading conditions. The filler metal should also have the desired penetration characteristics and appearance to match the weld geometry and aesthetic expectations.
5) Welding equipment and power:
The welding equipment and power are the tools and the electrical current that are used to generate the arc and the heat for the welding process. They may vary depending on the welding technique, the material thickness, and the weld joint configuration. The welding equipment and power can affect the arc characteristics, the heat input, and the weld quality. The filler metal should be compatible with the welding equipment and power, and have a good arc performance and a suitable heat input with the selected current and voltage. The filler metal should also minimize the weld spatter and the electrode consumption with the chosen welding technique and equipment.
II. Common Filler Metals for Welding Dissimilar Metals
There are many types of filler metals available for welding dissimilar metals, depending on the base metal combination, the welding process, and the application. Some of the most common filler metals are:
1) Austenitic stainless steel filler metals:
These are filler metals that contain chromium and nickel, and sometimes molybdenum, as the main alloying elements. They have a high corrosion resistance, a high ductility, and a low coefficient of thermal expansion. They are often used for welding dissimilar metals that involve stainless steel, carbon steel, low alloy steel, or nickel-based alloys. Some examples of austenitic stainless steel filler metals are 309 (L), 312, and 316 (L).
2) Nickel-based filler metals:
These are filler metals that contain nickel as the main alloying element, and sometimes chromium, molybdenum, iron, or copper, as the secondary alloying elements. They have a high corrosion resistance, a high strength, and a high ductility. They are often used for welding dissimilar metals that involve nickel-based alloys, stainless steel, carbon steel, low alloy steel, or copper alloys. Some examples of nickel-based filler metals are 82, 182, and 625.
3) Copper-based filler metals:
These are filler metals that contain copper as the main alloying element, and sometimes zinc, tin, silicon, or nickel, as the secondary alloying elements. They have a high electrical and thermal conductivity, a high ductility, and a low melting point. They are often used for welding dissimilar metals that involve copper alloys, such as brass, bronze, or cupronickel, or for brazing dissimilar metals, such as steel, cast iron, or stainless steel. Some examples of copper-based filler metals are ERCu, ERCuSi-A, and ERCuNi.
III. Advantages and Disadvantages of Welding Dissimilar Metals
Welding dissimilar metals can offer some advantages and disadvantages, depending on the application and the weld quality. Some of the advantages are:
Cost reduction: Welding dissimilar metals can reduce the material cost by using cheaper or lighter metals in less critical areas, and more expensive or heavier metals in more critical areas. For example, welding carbon steel to stainless steel can save the cost of using stainless steel for the entire structure, while still providing corrosion resistance in the exposed areas.
Performance improvement: Welding dissimilar metals can improve performance by combining different metal properties in a single structure, such as strength, corrosion resistance, ductility, hardness, or conductivity. For example, welding copper to steel can improve the electrical and thermal conductivity of the structure, while still providing strength and durability.
Design flexibility: Welding dissimilar metals can increase design flexibility by allowing the use of different metals for different shapes, sizes, and functions, without compromising the weld integrity. For example, welding aluminum to steel can enable the use of aluminum for complex or thin shapes, and steel for simple or thick shapes, without affecting the weld strength or appearance.
Some of the disadvantages are:
Weldability issues: Welding dissimilar metals can pose some weldability issues, such as poor bonding, cracking, or material failure, due to the differences in chemical composition, mechanical properties, and thermal expansion coefficients of the base metals. These issues can be mitigated by selecting the appropriate filler metal, welding process, and welding parameters, and by applying proper preheating and post-welding treatments.
Weld performance issues: Welding dissimilar metals can affect the weld performance, such as corrosion resistance, impact resistance, fatigue resistance, hardness, ductility, and appearance, due to the dilution, segregation, or precipitation of the alloying elements in the weld metal. These issues can be avoided or minimized by controlling the heat input, the weld penetration, and the weld geometry, and by choosing the right filler metal, shielding gas, and design requirements.
Weld inspection issues: Welding dissimilar metals can complicate the weld inspection, such as visual inspection, non-destructive testing, or destructive testing, due to the variations in color, texture, density, or hardness of the weld metal and the base metals. These issues can be overcome by using appropriate inspection methods, equipment, and standards, and by applying proper weld identification and documentation.
IV. Conclusion
Welding dissimilar metals is a useful technique that can lower the material cost, improve the performance, and increase the design flexibility of a structure. However, it also requires careful selection of the filler metal, which is the material that melts and flows between the two base metals to create a weld joint. The filler metal should be compatible with both base metals, and provide the desired weld characteristics and service requirements. Some of the common filler metals for welding dissimilar metals are austenitic stainless steel filler metals, nickel-based filler metals, and copper-based filler metals. Welding dissimilar metals can also present some advantages and disadvantages, depending on the application and the weld quality.
We hope this article has helped you learn more about the filler metal selection for welding dissimilar metals and how to use it effectively.
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