Friction Stir Welding process of AZ91 Mg and A319 Al alloys for improving the impact resistance, hardness and yield strength of the weld

چکیده مقاله

The purpose of this work is to study the effect of friction stir welding (FSW) parameters such as rotational velocity, welding speed and tilt angle on the impact resistance, hardness and yield strength using the response surface method. The microstructure of the obtained welds was analyzed by EDS, TEM and SEM images. Moreover, in this research, the peak temperature of the process and the thickness of the intermetallic layers have been estimated using the obtained experimental models. The results indicated that a rise of tilt angle up to 2° improved the impact resistance and yield strength of the weld by 44% and 26% respectively, while the weld hardness was improved by 7.2% with a tilt angle of 4°. In addition, an increment of welding speed from 40 to 60 mm/min led to a reduction of the grain size of the weld, which led to an improvement of the hardness (6%) and yield strength (46%), while it deteriorated the impact resistance (29%). Moreover, the increase of rotational velocity from 1000 to 1500 rpm enhanced the impact resistance (35%) and yield strength (23%) of the weld, but the further increase of rotational velocity up to 2000 rpm reduced the impact resistance (47%), yield strength (12.5%) and hardness (8.5%). The optimization results showed that the simultaneous enhancement of the yield strength, impact resistance and hardness can be achieved at rotational velocity of 1300 rpm, tilt angle of 2.1° and welding speed of 60 mm/min. In order to improve the quality of the weld under optimal conditions, a water spray system is used in the welding process, which sprays water at the center of the weld. The results have shown that by performing the FSW process under optimal parameter conditions along with water spray, the presence of intermetallic phases has been considerably reduced.