Figure 5-26.  Filler metal selection chart. ringlet is more pronounced. A good weld has a bead that is  not too proud and has penetration that is complete. Immediately after welding, the flux must be cleaned by using  hot (180 °F) water and the stainless steel brush, followed by  liberal rinsing with fresh water. If only the filler was fluxed,  the amount of cleanup is minimal. All flux residues must  be removed from voids and pinholes. If any particular area  is suspect to hidden flux, pass a neutral flame over it and a  yellow-orange incandescence will betray hiding residues.  Proper scrubbing with an etching solution and waiting no  longer than 20 minutes to prime and seal avoids the lifting,  peeling, or blistering of the finished topcoat.  Gas welding of magnesium is very similar to welding  aluminum using the same equipment. Joint design also  follows similar practice to aluminum welding. Care must be  taken to avoid designs that may trap flux after the welding  is completed, with butt and edge welds being preferred. Of  special interest is the high expansion rate of magnesium- based alloys, and the special attention that must be given to  avoid stresses being set up in the parts. Rigid fixtures should  be avoided; use careful planning to eliminate distortion.  In most cases, filler material should match the base material  in alloy. When welding two different magnesium alloys  together, the material manufacturer should be consulted  for recommendations. Aluminum should never be welded  to magnesium. As in aluminum welding, a flux is required  to break down the surface oxides and ensure a sound weld.  Fluxes sold specifically for the purpose of fusion welding  magnesium are available in powder form and are mixed with  water in the same manner as for aluminum welding. Use the  minimum amount of flux necessary to reduce the corrosive  effects and cleaning time required after the weld is finished.  The sodium-flare reducing eye protection used for aluminum  welding is of the same benefit on magnesium welding.  Welding is done with a neutral flame setting using the same  tip size for aluminum welding. The welding technique  follows the same pattern as aluminum with the welding being  completed in a single pass on sheet gauge material. Generally,  the TIG process has replaced gas welding of magnesium  due to the elimination of the corrosive flux and its inherent  limitations on joint design. Once the edges are tacked, begin welding by either starting  at the second tack and continuing on, or starting the weld one  inch in from the end and then welding back to the edge of  the sheet. Allow this initial skip-weld to chill and solidify.  Then, begin to weld from the previous starting point and  continue all the way to the end. Decrease the heat at the end  of the seam to allow the accumulated heat to dissipate. The  last inch or so is tricky and must be dabbed to prevent blow- through. (Dabbing is the adding of filler metal in the molten  pool while controlling the heat on the metal by raising and  lowering the torch.) Weld bead appearance, or making ringlets, is caused by the  movement of the torch and dabbing the filler metal. If the  torch and add filler metal is moved at the same time, the  The definition of joining two pieces of metal by brazing  typically meant using brass or bronze as the filler metal.  Brazing and Soldering Torch Brazing of Steel Magnesium Welding  5-19 Filler Metal Selection Chart Base Metals 4043 (a) 4047 5556 5183 5554 (d) 1100 3003 5005 5052 6061 5086 DO NOT  GAS WELD 5356 5183 5356 5556 5654 (c) 5356 5183 5556 5356 5183 5554 5556 5654 (d) 4043 (a) 5356 5183 5556 5654 (c) 5183 5356 5556 5554 (d) 4043 (a) 4043 (a) 5183 5356 5556 5554 (d) 5654 (c) 5356 5183 5556 4043 (a) 5183 5356 5556 4047 5183 5356 4043 (a,b)  4043 (a) 4047 5356 4043 (a) 5183 5356 5556 4043 (a,b) 5183 5356 5556 4043 (a,b) 1110 4043 (a) 6061 5086 DO NOT  GAS WELD 5052 5005 1100 3003 For explanation of (a. b. c. d) see below Copyright © 1997 TM Technologies (a) 4043, because of its Si content, is less susceptible to hot cracking   but has less ductility and may crack when planished. (b) For applications at sustained temperatures above ISOF because   of intergranular corrosion. (c) Low temperature service at ISOF and below. (d) 5554 is suitable for elevated temperatures. NOTE: When choosing between 5356, 5183, 5556, be aware that  5356 is the weakest and 5556 is the strongest, with 5183 in between.  Also, 4047 has more Si than 4043, therefore less sensitivity to hot cracking, slightly higher weld shear strength, and less ductility.