Mr. Davoud Ramazani, Dr. Saeid Jabbarzare, Dr. Masoud Kasiri-Asgarani, Dr Mojtaba Alchian,
Volume 9, Issue 2 (Journal OF Welding Science and Technology 2026)
Abstract
In this study, the effect of tool rotational speed in the double-sided friction stir welding (FSW) process on the microstructural characteristics, phase distribution, and hardness of annealed AA7075 aluminum alloy was investigated. Aluminum sheet specimens were welded from both sides at three tool rotational speeds of 800, 1000, and 1200 rpm and a constant traverse speed of 50 mm/min. After friction stir welding of the AA7075 alloy, the specimens were prepared for metallographic, microstructural, and mechanical examinations. Macrostructural and microstructural evaluations were carried out using appropriate chemical etching, optical microscopy, and scanning electron microscopy equipped with energy-dispersive spectroscopy (SEM–EDS). In addition, X-ray diffraction (XRD) analysis was employed to identify the phases and intermetallic compounds. The microhardness distribution across the transverse cross-section of the joint was also measured using the Vickers method in order to evaluate variations in mechanical properties across different weld regions. Microscopic examination of the weld zone revealed that increasing the tool rotational speed increased the weld zone width from approximately 6.5 to 8.3 mm. The average grain size decreased markedly, from 224 µm in the base metal to the range of 15–20 µm in the weld zone. XRD analysis confirmed the presence of MgZn2 and Al2CuMg/Al2Mg3Zn intermetallic phases. With increasing rotational speed, these precipitates became more spheroidal and finer in size. The distribution and size of precipitates in the weld zone changed significantly compared with those in the base metal; owing to the thermal and mechanical effects induced by tool movement, the precipitates became more dispersed and refined. The local hardness in the weld zone increased with increasing rotational speed, reaching approximately 165 HV, which represents a significant improvement compared with the base metal hardness of 135 HV. This hardness enhancement is attributed to grain refinement and an increase in the density of intermetallic precipitates, which contribute to improved mechanical strengthening. Moreover, all welded specimens were free from structural defects such as cracks or porosity, indicating excellent weld quality. The present results can provide an effective guideline for optimizing friction stir welding parameters in high-performance aluminum alloys.
