In this study two different welding processes have been considered, a
conventional tungsten inert gas (TIG) and a relatively new solid state welding
known as friction stir welding (FSW). TIG welding process has been performed on
Al 6061-T6 of thickness 4mm by using filler metal of Al-Mg alloy type (ER5356)
according to AWS classification metal with tungsten electrode (EWth-2) and arc
voltage of (12V). Various welding currents of (125, 160, 200, 225) Amp were used
under argon as shielding gas of flow rate of (15-20 cf / hour) and welding speed of
280 mm/min.
Friction stir welding is carried out using automatic milling machine with five
different welding or bed speeds of (25-50-80-100-125 mm/min) and five different
tool rotation speeds of (630-800-1000-1250-1600 rpm). Tool steel of type R18
consists of a shoulder with diameter of (20 mm) and pin of diameter (5.5 mm). Xray
radiographic inspection, tensile test and microhardness test of FSW and TIG
joints at optimum welding conditions were made.
The results indicate that the best tensile strength of FSW joints is 289 MPa and
joint efficiency is 79% which were welded with welding parameters of (1250 rpm,
800 rpm and 50 mm/min, 125 mm/min) respectively. While in case of TIG joint the
best tensile strength is 210 MPa and joint efficiency is 57%.
It was found that the microhardness hardness values in the TIG welded joints
are lower than that of the FSW joints. The formation of fine equiaxed grains and
very fine strengthening precipitates (Mg₂Si) in the stir or weld region are the
reasons for higher tensile strength and hardness of FSW joints compared to TIG