Page 27 - Welding of Aluminium and its Alloys

Welding metallurgy 19

2.7 Finely distributed porosity in TIG plate butt weld 6mm thickness.
Courtesy of TWI Ltd.

Liquid

Solubility, cm 3 per 100 g

0.69

T 660 °C
m
0.036

300 400 500 600 700 800 900
Temperature, °C
2.8 Solubility of hydrogen in aluminium.

pronounced that it is extremely difficult to produce a porosity-free weld in
aluminium.
Porosity tends to be lowest in autogenous welds.When filler metal is used
porosity levels tend to increase because of contamination from the wire. Of
the conventional fusion welding processes TIG has lower levels of porosity
than MIG due to this hydrogen contamination of the wire. Increasing the
arc current increases the temperature of the weld pool and thereby
increases the rate of absorption of hydrogen in the molten metal. Con-
versely, in the flat welding position increasing the heat input can reduce
porosity when the rate of gas evolution from the weld exceeds the rate of
absorption – slowing the rate at which the weld freezes allows the