An aluminum electrode, flux covered, is used with a direct current reverse polarity (DCRP) circuit. The aluminum electrode is the positive pole. Important factors to be considered when using the SMAW process on aluminum are moisture, preheating, flux, and the cleanliness of the electrode and work. Presence of moisture in the electrode covering is a major cause of weld porosity. Dry, clean storage for electrodes is necessary for sound welds, so make sure you store electrodes properly. Deterioration of the flux covering can be rapid when the electrodes are exposed to moist air, and the entire covering can be affected in only a few hours of exposure to a humid atmosphere. Preheating of the work is sometimes necessary, especially in the thicker materials. Preheating to around 400 degrees F helps maintain the weld puddle and results in a more stable arc. This is the weld quality improvement that Skyhawk Greg mentioned. The flux that covers the electrode is very tenacious, and considerable operator skill is required to keep from entrapping it in the weld. Thoroughness in postweld removal of flux is important too. Most of the flux can be removed by wire brush, slag hammer, or peening hammer, and the rest by steaming or by a hot water rinse. To test for complete flux removal, swab a solution of 5% silver nitrate on welded areas. Foaming will occur if flux is present. One difficulty with SMAW, caused by interruption of the arc, is the formation of a fused flux coating over the end of the electrode. Re-establishing a satisfactory arc is near impossible until this formation is removed, usually by striking the electrode against the work, or another surface. Another difficulty is that because the aluminum electrode and base metal melt and resolidify almost immediately as welding progresses, electrode sticking can be a problem. Based on a 300 to 400 degree F preheating, your amp range should be as follows: 1/8 dia. rod 80-120 amps, 5/32 dia. rod 100-150 amps, 3/16 dia. rod 125-200 amps.