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17

Technical Services

Dilution

Dilution Ratios of Joints

Weld Composition: Dilution Effect

A weld essentially becomes a new alloy made up of the base and filler alloys. Dilution is the amount of base alloy that mixes

with the filler alloy to create the new weld alloy. There are multiple factors that affect the amount of base dilution into the

weld puddle. Although the welding parameters can change the dilution ratio, the easiest way to actually control it is by

modifying the joint design (see images below).

Depending on the alloys involved, simply changing the joint design may be enough to change the tensile strength of an

as-welded groove assembly. The image below shows the theoretical difference in dilution ratios by modifying the joint

design from a square butt to a single V-groove. The amount of base metal that is diluting the filler alloy is reduced in the

single V, making the overall magnesium content of the new weld alloy significantly higher.

Depending on the other variables involved, this may be all that is needed to go from just missing the minimum tensile

strength to achieving it regularly (and with room to spare). Another benefit of reducing the amount of base metal dilution

is that the probability of stress cracking is typically reduced.

80% Filler Metal

20% Base Metal

60% Filler Metal

40% Base Metal

20% Filler Metal

80% Base Metal

1.7% Mg

3.2% Mg

60% Filler Metal

40% Base Metal

20% Filler Metal

80% Base Metal

Base Plate

6061

Filler Metal

5356