Fabrication and characterization of Al alloy composites reinforced with nanocrystalline Al4CrFeMnTi0.25 high-entropy alloy particles via double ultrasonic stir casting for aerospace applications

Abstract

The aim of the present work is to fabricate the Al alloy-based composites by using a new class of High Entropy Alloy (HEA) reinforcement particles for aerospace applications, addressing the limitations associated with traditional ceramic reinforcement particles. Therefore, the present work is to fabricate an Al-7150 alloy-based composite by incorporating a novel nanocrystalline Al4CrFeMnTi0.25 HEA (NCHEA) reinforcing particle (0.5, 1, 1.5 and 2 wt%) through a double ultrasonic two-step stir casting technique. The relative density decreases with the addition of NCHEA particles in the mixture, however, the porosity remains below 5 % due to double ultrasonication. The grain size was significantly refined with the addition of NCHEA particles. The AA7150-HEA composite exhibits a “stone in mud” structure in which the HEA particles (stone) are embedded in an aluminum matrix (mud) due to the high density of NCHEA reinforcement. The AA7150–1.5 wt% HEA composite exhibited a small average crystallite size of 27.03 nm and a maximum dislocation density of 2.67 nm-2 analysed by X-Ray Diffraction (XRD) analysis. The AA7150–1.5 wt% HEA alloy achieved a maximum Vickers microhardness of 214.49 HV and an ultimate tensile strength of 218.37 MPa, which were 37 % and 27.5 % higher, respectively, compared to the base Al-7150 alloys. Failure usually occurs at the interface where the alloy is bonded to the ceramic reinforcement, however, in the HEA-reinforced composite, this fall-off action does not occur as observed by fractographic analysis. Nonetheless, Al7150–2wt% HEA-composites have many cracks on the fractured surface due to the agglomeration of NCHEA particles in composite. The NCHEA reinforcement particles can be incorporated into the Al7150 matrix as an alternative to ceramic reinforcements, enabling enhanced strength improvement.