Metals that are easiest to weld in resistance welding are ones that have low resistivities since low resistivity assists in the flow of electrical current:

Question

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metals with low resistivities, such as aluminum and copper, are difficult to weld in RW.Higher resistance is required in the conversion of electrical power to heat energy; hence, metals with high resistivity are generally preferable.

Metals That Are Easiest to Weld in Resistance Welding Are