The Maxxx pump housings and stator sections are stainless steel, the bearing carrier (which is pressed into the stainless steel hub) and pump cone on the Maxxx pump are aluminum.
The stator vanes in the Maxxx pump appear to be TIG welded to the pump housing.
2% Thoriated tungsten electrodes (red band) are typically used for welding stainless steel with DC straight polarity - electrode negative. The end of the electrode is ground into a fine point which allows for a more focused arc with lower welding currents. This helps produce the narrow weld beads commonly found on stainless steel parts.
Pure tungsten, zirconiated tungsten, or 2% ceriated tungsten (green, brown, and orange band) electrodes are used for welding aluminum with alternating current. Typically a sphere is formed on the end of the tungsten electrode by momentarily striking an arc with the welder set in DC reverse polarity - electrode positive. A point with a truncated end can be also be used. Both equate to a less focused arc and typically a wider weld bead.
Aluminum is difficult to weld because the naturally occurring protective oxide needs to constantly be removed. This is accomplished with alternating current. The aluminum is cleaned and the oxides are removed with reverse polarity - electrode positive, and the welding takes place in straight polarity - electrode negative. With a lot of the higher end TIG welders, you can adjust the balance control to alter the EN/EP ratio of the wave. With more EN time you can create a narrower weld bead with deeper penetration. More EP time promotes better cleaning and oxide removal (which is important when welding cast aluminum like the OEM pump housings) but crates a much wider weld bead with shallower penetration depths.
