Saeid Nader - Department of Materials Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran
Masoud Kasiri- Asgarani - Department of Materials Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran
kamran amini - Department of Mechanical Engineering, Tiran Branch, Islamic Azad University, Isfahan, Iran
Morteza Shamanian - Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, Iran

In this study, friction stir spot welding (FSSW) is applied to join the TiAl۶V۴ titanium alloy with ۱.۵ mm thickness and then the effect of rotational speed and tool dwell time on microstructure and mechanical properties is investigated. In this regard, the speed of the tool rotation was considered as ۸۰۰, ۱۰۰۰, and ۱۲۰۰ rpm, as well as the tool dwell time was set at ۷ and ۱۲s. Microstructural evaluation was carried out using optical microscopy (OM) and scanning electron microscopy (SEM). In addition, tensile-shear and hardness studies were performed to analyze mechanical properties. The obtained results from microstructural evaluation show that the welded joints consist of two regions, namely the SZ and the HAZ-regions. Additionally, microstructure of the SZ-region was identified in the form of α/β layer within the initial β-phase. The results of tensile/shear tests and micro-hardness test indicated that the joint strength and hardness are enhanced with increasing the rotational speed and dwell time. The tensile/shear strength is increased from ۲.۷ to ۱۵ KN with increasing the rotational speed at constant dwell time of ۷s, and also is increased from ۷.۳ to ۱۷.۲۵ KN with increasing the rotational speed at constant dwell time of ۱۲s. The maximum tensile/shear strength was achieved for the welded joint with the dwell time of ۱۲s and rotational speed of ۱۲۵۰ rpm. The hardness of SZ, HAZ regions and base metal are measured around ۳۸۰ to ۴۲۰, ۳۴۰ to ۳۸۰, and ۳۰۰ to ۳۴۰, respectively.

Dwell time, Friction stir spot welding, Rotation speed, Titanium alloy