Welding of Dissimilar Joints

Difficulties

• The process of welding dissimilar joints presents a variety of difficulties. V.M. Radhakrishnan, author of the book “Welding Technology & Design,” identifies three primary difficulties. According to Radhakrishnan, differences in the physical properties of metals can cause problems during the welding process and afterward, if not properly welded. Furthermore, the use of an improper filler material during welding can lead to problems like weakening of metals, weak joints and increased corrosion susceptibility. Finally, new compounds made of dissimilar metals can form at the joint site and lead to the formation of brittle material that breaks easily.

Welding Methods

• Various types of welding exist -- though not all are suited to welding dissimilar joints. According to a paper published by the American Welding Society, arc welding and resistance spot welding work best for welding dissimilar joints. Arc welding entails using a welding machine that creates an electrical current, or arc, between metal and machine. This arc melts the metal at the point of contact. Resistance spot welding consists of heating a spot from both sides using an electric current transferred from a pair of electrodes to the spot.

Filler Metals

• Welding dissimilar joints requires the use of filler metals. Fillers comprise a group of metals used in small quantities during welding to help join dissimilar metals in a way that encourages compatibility between the materials and helps prevent problems like corrosion and embritllement. The type of filler you use depends completely on the types of metal you want to weld. For instance, when welding different types of steel, use a third type of steel with properties similar to the other two as a filler. You can find charts of ideal filler materials online or speak with a metal worker or other welding expert in your area for ideas.

Temperature

• Welding temperature heavily affects the success of welding dissimilar metals. For instance, Joseph R. Davis, author of the book “Copper and Copper Alloys,” recommends welding steel to copper at 1000 degrees Fahrenheit. Welding steel to silicon bronzes, however, requires a maximum temperature of 150 degrees Fahrenheit. Always follow temperature recommendations to avoid problems such as embrittlement and an over-dilution of filler in welded metals. Author V.M. Radhakrishnan stresses the importance of welding at the lowest heat level necessary to avoid many of the problems associated with the process. You can find charts on ideal welding temperatures in books and online.