Evaluation of the mechanical properties of friction stir lap welded joints for dissimilar aluminum alloys(AA1100 To AA6061)
In this study friction stir lap welding (FSLW) joints are made for similar and dissimilar aluminum alloys (AA1100 to AA6061-T6) sheets of 3mm thickness by varying the welding parameters, such as tool rotation speeds (1000, 1250 & 1600 rpm) and welding speeds (35, 75 & 100 mm/min) and pin length of (2.8, 5.4 & 5.7mm) with using cylindrical threaded tool pin profile. Many tests and inspections were performed such as X-Ray radiographic and tensile shear test to evaluate the weld quality and joint efficiency under different welding parameters. Microhardness and microstructure observations were carried out at the best welding parameters. The maximum tensile shear force (4.93 KN) and joint efficiency (93%) were obtained when welding process was conducted by a new technique with using friction stir diffusion welding process at the welding speed of 75 mm/min, tool rotation speed of 1250 rpm and using pin length of 2.8 mm. It was found that the Vickers hardness of the similar and dissimilar joints reached to the maximum value at stir zone and drop toward the base metals.
A Comparison Study of Mechanical Properties between Friction Stir Welding and TIG Welded Joints of Aluminum Alloy (Al 6061-T6)
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 joints.
Phase formation during mechanical alloying in the Ti–Si system
Abstract Mechanical alloying of Ti–Si powder mixture or TiH 1.924 –Si powder mixture was performed by high-energy ball milling, in which the Ti to Si mole ratio was 1:2. The phase formations in both mixtures during milling were investigated by X-ray diffraction. Mechanical alloying a mixture of elemental powders led to the formation of TiSi 2 equilibrium compound, while when starting from Si + TiH 1.924 , a metastable phase was formed. The metastable phase completely transforms to TiSi 2 when the mechanically alloyed powder is annealed at temperatures above 800 °C. Two different pathways of phase transitions during mechanical alloying are attributed to the existence of hydrogen atoms, i.e., when starting from Si + TiH 1.924 compared to Si + Ti, the kinetics for the formation of the TiSi 2 intermetallic compound slows down. The kinetics related to the different phase transitions depending on the starting powder mixture are discussed.