[ezg55]

When TIG welding aluminum it if best to clean using IPA to insure that all oils, paint, etc are removed. Mechanical cleaning is only needed when the aluminum has been anodized. Grind the weld area using a grinding wheel made for aluminum. You can find this grinding wheel at your welding supply store. It is dangerous to use a grinding wheel designed for carbon steel on aluminum because the aluminum can build up on the wheel and overheat causing it to shatter. Pre-heating thick aluminum plate is ok since it will remove any residual moisture and make it easier to weld. Do not exceed 600 degrees Fahrenheit or quench the aluminum while hot since this will anneal the metal and make it soft.
Avoid contamination of the weld area by not removing the TIG torch shielding gas or the filler rod from the weld area for a few seconds after you stop the weld. Also during the welding process try to keep the filler rod close to the TIG cup to prevent the filler rod from being exposed to air which will oxidize it. As you move the rod back into the weld puddle you will cause contamination of the weld area. A good TIG welder can lay a bead, with a 36 inch filler rod, feeding with one hand without stopping with perfect weld width and height. Keep up the practice.