S. Rouhi - Department of Mechanical Engineering, Faculty of Engineering, Urmia University, Urmia, Iran
A. Doniavi - Department of Mechanical Engineering, Faculty of Engineering, Urmia University, Urmia, Iran
M. Shahbaz - Department of Materials Science and Engineering, Faculty of Engineering, Urmia University, Urmia, Iran

In this research, friction stir welding (FSW), a solid-state joining process, was employed to weld ۵ mm thick sheets of aluminum alloy Al۲۰۲۴ and magnesium alloy AZ۹۱C. The Taguchi design of experiments method was utilized to optimize the FSW process parameters including tool rotational speed (۸۰۰-۱۶۰۰ rpm), welding speed (۸-۲۰ mm/min), and plunge depth (۰.۲-۰.۴ mm) to achieve maximum hardness in the weld zone. Microstructural characterization was studied using optical and scanning electron microscopes. The optimum parameters were found to have a ۱۶۰۰ rpm rotational speed, ۸ mm/min welding speed, and ۰.۴ mm plunge depth, resulting in a maximum hardness of ۱۴۸ HV in the stir zone (SZ). The layered or onion ring structure observed in the SZ was attributed to insufficient mixing and elemental diffusion between the dissimilar alloys due to the short interaction time during welding. Scanning electron microscopy revealed the formation of a continuous intermetallic layer at the aluminum-magnesium interface and the dispersion of magnesium particles in the aluminum matrix, contributing to the composite-like structure in certain regions. The hardness variation perpendicular to the weld line was correlated with the microstructural evolution, with the highest hardness observed in the fine-grained SZ due to grain refinement and precipitation hardening. The thermomechanically affected zone (TMAZ) exhibited lower hardness due to the presence of coarser precipitates and partially recrystallized grains. This research demonstrates the feasibility of joining Al۲۰۲۴ and AZ۹۱C alloys using FSW and highlights the importance of optimizing process parameters to achieve desirable mechanical properties and microstructural characteristics in the dissimilar weld joint.

Optimization, Friction Stir Welding, Dissimilar joining, taguchi method