m movahedi - Associate professor, Materials Science and Engineering Department, Sharif University of Technology
m mohseni rad - M.Sc. student, Materials Science and Engineering Department, Sharif University of Technology
a ozlati - PhD student, Materials Science and Engineering Department, Sharif University of Technology

In this research, the effect of thetool rotational speed on microstructure of the friction stir lap joined aluminum/polypropylene-elastomer-talc composite and the possibility of improving the mechanical properties of joints via surface treatment of the aluminum was investigated. Macrostructural studies showed that macroscopic mechanical locks (in the form of anchor-like aluminum pieces piercing into the composite sheet) form as a result of the joining process. The size and orientation of these anchors changes with tool rotational speed. A reaction layer (with a thickness of ~10-20 micrometers) containing C, O and Al atom forms at the stirred zone/aluminum interface via erosion mechanism and solution of aluminum atoms in the melted composite. Porosities with different sizes form on aluminum surface by chemical surface treatment process as surface roughness increased by ~2.5-4.5 times compared to un-treated samples. Porosities on the aluminum surface promote formation of microscopic mechanical locks (via penetration and solidification of melted composite inside the pores) across the overlapped area of the joint. Increasing tool rotational speed results in enhancement of the joints fracture load in tensile-shear test up to ~320 N in the optimal rotational speed. Microscopic mechanical locks noticeably increase fracture load (from ~40 to 170% in different rotational speeds and surface roughness) and play an important role in improvement of the joints mechanical properties.

Aluminum AA5052, Polypropylene-based composite, Surface treatment, Mechanical properties, Macrostructure