Influence of Insoluble Elements Addition on Microstructural Stability and Strengthening Mechanisms of Spark Plasma-Sintered Al–Cu Alloys

Abstract

Abstract. The present investigation explores the microstructural stability, mechanical properties, and strengthening mechanisms of spark plasma-sintered (SPSed) nano/ultrafine grained AlCuZr, AlCuNb, and AlCuY alloys for lightweight structural applications. The SPS was carried out at the temperatures 350, 450, and 550 °C on cryo-ball-milled Al4.5%Cu1%Zr, Al4.5%Cu1%Nb, and Al4.5%Cu1%Y alloys. For all these samples, the spark plasma sintering (SPS) at 550 °C has shown the highest densification and found to be 97%, 97%, and 98%, respectively. This is due to exceptional diffusion bonding between the particles. The corresponding average grain size measured in nanometers (i.e., less than 100 nm) was confirmed by transmission electron microscopy (TEM) microstructural analysis. Similarly, the yield strength (YS) for the AlCuZr, AlCuNb, and AlCuY alloys was measured to be 620, 615, and 600 MPa, respectively. These are significantly superior to those alloys SPSed at 350 and 450 °C. An improved mechanical property at 550 °C is due to the insoluble stabilizer (i.e., Zr, Nb, and Y), which acts as an obstacle to the movement of grain boundaries and accumulation of more dislocations (strain hardening). Furthermore, the strengthening mechanisms were also quantified by considering experimental data [i.e., alloying, TEM, and X-ray diffraction (XRD)] and comparing with test data (YS). Grain size reduction is observed to be a significant strengthening mechanism for the YS as contrasted to the other mechanisms.