Welding alloys are used to melt and fuse pieces of metal together. They are used in stick electrode welding, metal inert gas (MIG) welding, tungsten inert gas (TIG) welding, and flux cored arc processes. Stick electrode welding or shielded metal arc welding melts the flux to form a gas which shields the arc and molten weld-pool. MIG wire welding or gas metal arc welding (GMAW) joins metal by melting the base and filler metals with an arc struck between a consumable filler metal wire and the metal alloy workpiece. TIG rod welding or gas tungsten arc welding (GTAW) is similar to GMAW, but does not make the tungsten electrode part of the completed weld. Flux cored arc welding or flux core wire welding is also similar to MIG welding, but uses a wire with a central core that is filled with flux. Welding alloys for stud welding and other specialized processes are also commonly available.

There are many different types of welding alloys or fillers. Suppliers usually designate products as suitable for welding aluminum, cast iron, copper, magnesium, nickel, steel, titanium, or zirconium. Steel alloys include carbon steel, low-alloy carbon steel, stainless steel, and tool steel (high-alloy steel). Specialized welding alloys are used to join castings or restore a specific layer of a work surface. Typically, these fillers are highly alloyed to develop the required properties. Examples include welding alloys for build-up or joining, overlay, high abrasion resistance, high impact and abrasion resistance, and corrosion and heat resistance. Low hydrogen filler alloys are also available. These welding alloys are often used to avoid the development of hydrogen embrittlement or hydrogen-assisted cracking in welded steel components.

Welding alloys vary in terms of shape, properties, and electrode type. Choices for form or shape include composite or trimet, paste, powder, preform, solid wire, strip, sheet, foil, thermite mix, tubular wire, and weld. Tensile strength, yield strength, elongation, melting range, and conductivity are important properties to consider. Universal tensile strength (UTS) is the breaking load. Yield strength is the applied stress under which welding alloys experience plastic deformation. Elongation is the increase in length of a metal stressed in tension. Melting range is the range of temperatures over which filler alloys melt. With regard to tips or electrodes, choices include resistance welding electrodes or horns, TIG electrodes, and cutting or gouging electrodes.