What issues arise from dissimilar metal welding and how are they mitigated?

• A. Electrical conductivity changes make joints fail.
• B. Thermal shock causes cracking only.
• C. Galvanic corrosion and differences in thermal expansion; mitigated by electrode selection, coatings, thermal compatibility, and electrical isolation where needed.
• D. Color mismatch leads to poor aesthetics.

Answer: (C)

When welding different metals, two main problems can show up: galvanic corrosion and differences in how the metals expand and contract with temperature. Galvanic corrosion happens when dissimilar metals are joined and in the presence of an electrolyte (like moisture). They form a galvanic couple, where the more anodic metal corrodes faster while the other metal is protected. This accelerates deterioration right at the joint.

To reduce this risk, choose a filler metal and electrode chemistry that brings the electrochemical potentials of the weld area closer to each metal, so the driving force for galvanic current is smaller. Applying barrier coatings or selective coatings on one or both sides creates a physical barrier to electrolytes, preventing the joint from being exposed to moisture-based buildup. Electrically isolating the metals where the joint contacts an electrolyte—using insulating barriers or coatings—stops the galvanic current from flowing.

The second big issue is differential thermal expansion. When the metals heat up and cool down, their differing coefficients of expansion cause thermal stresses, which can crack the weld or distort the structure. Mitigation includes picking metals with more compatible thermal expansion behavior, controlling heat input during welding to reduce gradients, preheating to lessen the temperature difference between base metals, and applying post-weld heat treatment or stress-relief procedures to relieve residual stresses.

In short, dissimilar metal welding is managed by careful material and filler selection, protective coatings or barriers, controlling heat input and temperature effects, and, when needed, isolating the metals electrically to prevent galvanic action.