TABLE 4-12. SPECIFICATIONS APPLICABLE TO WELDING MAGNESIUM ALLOYS.
Arc Welding - Gas Welding
Heat Treatment of Castings
Qualification of Welds
Fluorescent Penetrant Inspection
Welding Resistance Aluminum, Magnesium,
Non-Hardening Steel or Alloys, etc.(Spot
Welding Repair of Castings
4-52. Safety precautions in welding are set forth in separate paragraphs herein. These precautions should be reviewed
and adhered to at all times. Of prime importance is the proper technique for the welding of thorium containing alloys
(see paragraph 4-14).
4-53. GAS WELDING. This type welding, although once the predominant method for fusion joining magnesium, has
been generally replaced by other methods. One of the main reasons is its inherent weakness for corrosion from the flux
used with welding. For this reason only butt type joints are recommended in gas welding. In a lap type joint, flux
deposits would be trapped in the lap, leading to destructive corrosion of the joint. After welding of a joint all traces of flux
must be removed. Procedures for this are contained in later paragraphs. Welds should be made in one pass, therefore,
only material up to ¼ " can be welded. The general present practice is to use gas welding as an emergency repair
procedure of magnesium assemblies. Thin sheet may continue to be welded using butt joints.
4-54. Equipment. Torches used have tip sizes of 0.035" to 0.081" or 0 to 1 for 0.032" thick material and size 3 or 4 for
0.128" stock. The gases are oxygen, acetylene and oxy carbohydrogen (80% hydrogen 20% methane). The last gas is
particularly satisfactory for welding stock up to 0.064" thick due to its soft flame. Acetylene is used with oxygen for
thicker gauges. See Table 4-13 (or a general guide to regulation of welding equipment.
4-55. Welding Rods. Welding rods recommend for use in welding alloys ire listed in Table 4-14, for joining wrought
alloy, Table 4-15 for joining cast to wrought alloy, and Table 4-16 for joining cast to cast alloys. If a rod is not specified
for an alloy, use one of the same composition as alloy involved.
4-56. Flux. Fluxes for use in welding magnesium are cited in Table 4-17. The flux is usually supplied in powder form
and shall be kept dry until mixed for use. Flux should be mixed in approximately the quantity required for the job on
hand by mixing 2 parts of water to I part powder by volume. Keep paste covered when not in use.
4-57. WELDING PROCEDURES. Surface preparation is the first step required if a good welded joint is to be expected.
The surface to be fused should be cleaned of all material down to the base metal. Chemical cleaning is preferred over
mechanical methods, if possible, as its action provides uniform longer life cleanliness. Parts should be degreased if their
condition requires it, washed thoroughly in a hot alkaline cleaner and then immersed for about 3 minutes in a 70
bath of 24 oz Chromic Acid (CrO3), 4 oz Sodium Nitrate (NaNO3) and enough water to make one gallon of solution (Type
I in accordance with MIL-M-3171). Any amount of solution may be used in these proportions. Rinse thoroughly in hot
water and air dry. If chemical cleaning is not possible, the surface should be degreased with a solvent such as
trichloroethylene, solvent specification P-D-680, Type II or alkaline cleaner Specification MIL-C-25769 and then cleaned
with steel wool, 2luminum oxide cloth or stainless wire brushes. Insure the surface is free of all loose and imbedded
abrasive material. If the work is a repair, the edges of the defect must be dressed down to clean sound metal to a 450
slope. Leave a land or root face of about 1/18" at the bottom of defects which penetrate through the surface. For joining
of sheets, etc., the surface must be cleaned as above and a suitable gap may be left between the sheet edges to allow
for shrinkage and warpage. A gap 1/16 for thinner materials 0.040" and below, gradually increasing through gauge
ranges to 3/8" gap for 14" material is satisfactory.