GMAW transfers metal in three ways. At low currents, you get short-circuit transfer, in which the molten droplet on the GMAW wire makes contact with the work. This works well for steel wires, but not for aluminum because the weld isn’t hot enough to overcome aluminum’s high thermal conductivity, and lack-of fusion defects often result. If you raise the current above the transition current, you get spray transfer, in which magnetic forces transfer tiny droplets across the arc. Spatter levels are low, the weld is hot enough to avoid lack-of-fusion defects, and you can weld out of position. Spray transfer is recommended for aluminum GMAW. So why not just spray-transfer aluminum? Why consider pulsed spray? Because while spray transfer isn’t a problem for thick aluminum, it is for thinner aluminum. The transition current for 3/64-in. aluminum wire is approximately 135 amps. This is the minimum current you can use to spray transfer-weld aluminum with this wire. While that’s fine for materials thicker than 5/32 in., what about thinner materials? Pulsed spray GMAW power supplies pulse the current between a peak current above the transition current and a background current significantly below the transition current. Wire droplets are transferred across the arc in spray transfer when the arc is at peak current, but no droplet transfer takes place when the arc is at background current. What’s the net effect? You can get spray transfer at average currents well below the transition current. That makes it easier to weld thin aluminum, weld out of position, and train new welders to GMAW aluminum. However, pulsing power supplies are more complex, so they cost more. Pulsed GMAW power supplies aren’t a panacea. Use them where it makes sense—for thin aluminum and out-of-position welding.