Английский язык для инженеров сварочного производства. Гричин С.В - 74 стр.

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maximum temperature reached is of the order of 0.8 of the melting

temperature.

Fig. 11 Tool in operation

Fig. 12 HAZ

The tool has a circular section except at the end where there is a

threaded probe or more complicated flute; the junction between the

cylindrical portion and the probe is known as the shoulder. The probe

penetrates the work piece whereas the shoulder rubs with the top surface. The

heat is generated primarily by friction between a rotating-translating tool, the

shoulder of which rubs against the work piece. There is a volumetric

contribution to heat generation from the adiabatic heating due to deformation

near the pin. The welding parameters have to be adjusted so that the ratio of

frictional to volumetric deformation--induced heating decreases as the work

piece becomes thicker. This is in order to ensure a sufficient heat input per

unit length.

The microstructure of a friction-stir weld depends in detail on the tool

design, the rotation and translation speeds, the applied pressure and the

characteristics of the material being joined. There are a number of zones. The

heat-affected zone (HAZ) is as in conventional welds. The central nugget

region containing the onion-ring flow-pattern is the most severely deformed

region, although it frequently seems to dynamically recrystallise, so that the

detailed microstructure may consist of equiaxed grains. The layered (onion-

ring) structure is a consequence of the way in which a threaded tool deposits

material from the front to the back of the weld. It seems that cylindrical

sheets of material are extruded during each rotation of the tool, which on a

weld cross-section give the characteristic onion-rings.