Evaluation of Microstructure, Hardness and Mechanical Properties of Friction Stir Welded Al–Ce–Si–Mg Aluminium Alloy

Abstract

Abstract: A vast majority of the research on friction stir welding(FSW) is mainly focused on welding of aluminium alloys. The research studies in this paper are based on one such alloy known as Al–Ce–Si–Mg aluminium alloy, of which, the microstructure and other mechanical properties of the friction stir welded joints are yet to be studied. The plates of Al–Ce–Si–Mg aluminium alloy were friction stir welded using a non consumable, rotating tool with triangular profile pin and circular shoulder, with different combinations of tool rotation speeds and weld speeds. The microstructure, hardness and mechanical properties of the weld were analyzed. The microstructure of the weld zones revealed that, the average grain size at the bottom of the Nugget Zone (NZ) is 5 ± 0.12 μm and gradually increases to 15 ± 0.23 μm at the top of the NZ. In the TMAZ the grain size is 20 ± 0.14 μm and is bigger compared to the NZ. In the HAZ, the grain size is around 37 ± 0.21 μm and is bigger than that in the TMAZ. The maximum Vickers hardness value at the NZ center is 231.9 ± 2 Hv, and uniformly reduces to 100 ± 2.4 Hv in the TMAZ and 65 ± 1.3 Hv in the HAZ and then increases to 98 ± 1 Hv in the base material (BM). The maximum ultimate tensile strength (UTS) of FSW joint was found to be around 102.55 ± 3 MPa with elongation at fracture of 2.5%. The BM UTS was 154 ± 4.5 MPa. For a tool rotation speed of 800RPM and a weld speed of 20 mm/min a maximum joint efficiency of 67%. was obtained. Hence these were chosen as the optimum process parameters to join the alloy Al–Ce–Si–Mg by FSW. Graphic Abstract: [Figure not available: see fulltext.] © 2019, The Korean Institute of Metals and Materials.