The results showed that the microhardness and tensile strength of the heat-affected zone as the weakest welding zone in some samples reduced up to 30% compared to the base metal. On the other hand, a decrease in rotational speed, an increase in tool movement speed, and the number of welding passes cause grain refinement and improve mechanical properties. However, the effect of decreasing the rotation speed and increasing the tool movement speed were shown to be more favorable due to less heat production. Accordingly, the hardness in the welded zone with a rotational speed of 600 rpm and a movement of 80 mm/min increased from 90 to 125 HV compared to the base metal, and the hardness reduction in the zones around the welded zone was only 5 Vickers. It was also found that reducing the grain size of the stir zone, while improving the mechanical properties leads to increasing the density of the surface pasive layer, preventing the attack of aggressive chlorine ions and thus reducing the corrosion intensity by 50 times in saline seawater.
