Page 182 - Welding of Aluminium and its Alloys

Other welding processes 165

Table 8.3 Tensile test results for a range of friction stir welded alloys

Material 0.2% proof strength UTS Elongation Softening factor
2
2
(N/mm ) (N/mm ) (%)
5083 O 141 298 23 1.00
5083-H321 153 305 22.5 0.91
6082-T6 160 254 4.85 0.83
6082-T6 aged 274 300 8.4 1.00
6082-T4 138 244 18.8 0.93
6082-T4 aged 285 310 9.9 1.19
7108-T79 210 320 12 0.86
7108-T79 245 350 11 0.95

results of mechanical tests carried out by TWI Ltd as part of the investiga-
tory programme. The results show that the ‘softening factor’, the ratio
between the parent metal strength and that of the weld, in both the cold-
worked and age-hardened alloys, is close to 1, implying that there is a
limited loss of strength.
The softening factors of 0.83 for the 6082-T6 alloy can be compared with
the softening factor of 0.50 in Table 4.5 of BS 8118 for an arc weld in the
same alloy and condition. The design benefits once this reduction in
strength loss can be taken advantage of in the design specifications are
obvious.
Plate of 75mm thickness has been welded using a double sided technique
at a welding speed of 60mm per minute. Plates in the thickness range
1.2–50mm have been welded in a single pass and at speeds of up to
1800mm/min. The process is completely mechanical and can be carried out
with simple machine tool equipment that requires very little maintenance.
The conventional non-destructive testing techniques of radiography and
ultrasonic examination do not lend themselves to the interrogation of
friction welds. However, the welding parameters are machine tool settings
and can be easily monitored and used to determine weld quality, any
deviation from the required settings being cause for rejection.
Although this development is relatively recent it has been enthusiasti-
cally adopted by the rail rolling stock manufacturers and a number of ship-
yards in addition to its use in the aerospace industry.