Influence of insoluble elements addition on microstructural stability and strengthening mechanisms of spark plasma sintered Al-Cu Alloys

The present investigation explores the microstructural stability, mechanical properties and strengthening mechanisms of spark plasma sintered (SPS) nano/ultrafine grained AlCuZr, AlCuNb, and AlCuY alloys for lightweight structural applications. The SPS was carried out at 350, 450, and 550 °C on cryo-ball milled Al4.5%Cu, Al4.5%Cu1%Zr, Al4.5%Cu1%Nb, and Al4.5%Cu1%Y alloys. When SPS was carried out at 550 °C, the highest densification was found to be 97%, 97%, and 98%, respectively, for all the samples. 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 TEM microstructural analysis. Similarly, the yield strength (YS) was measured to be 620, 615 and 600 MPa, respectively, for the Al4CuZr, AlCuNb, and AlCuY alloys, which are significantly superior to those alloys SPSed at 350 and 450 °C. An improved mechanical property at 550 °C is due to the insoluble stabiliser (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 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.