Microstructure and Mechanical Properties of 2024 Aluminum Alloy with and Without Rare-Earth and Thermomechanical Treatment After Multi-pass Stir Friction Processing

Abstract

Friction stir processing (FSP) is the most effective severe plastic deformation process for creating materials with very fine grains and good properties. The target of the present research is to investigate the influence of FSP on the microstructure and mechanical properties of homogenized 2024 aluminum alloy with and without rare-earth (RE) and thermomechanically treated conditions (TMT). The rare-earth elements used were Ce and La in the form of a master alloy containing (50% Ce + 50% La). The casting of 2024 aluminum alloys, both with and without (Ce + La), was carried out using the conventional stir cast technique. Part of the obtained alloys was homogenized, whereas the other part was thermomechanically treated (TMT). The homogenized 2024 material was exposed to FSP with multiple passes (one, two, and three) to obtain the suitable pass number. After that, the best pass number was performed on the 2024 aluminum alloy refined with RE (Ce + La) and TMT materials. The microstructures in different conditions (homogenized and stir friction) were examined by optical and scan microscopes attached with EDS and Map analyzer. At the same time, a tensile test was conducted to assess the mechanical properties. The findings indicated that the microstructures were significantly refined after adding RE (Ce + La) or applying the TMT technique. Whereas, the microstructures were greatly improved after applying FSP to both conditions. Ultra-fine grains were observed for both TMT and RE-containing alloys after FSP. On the other hand, the results of mechanical properties were significantly increased after applying multiple passes of FSP. The optimum results were obtained when two passes of stir friction were applied to the TMT alloy condition.