Sc-induced great increase in high temperature strength of Al-Si-Cu heat-resistant alloy

The effect of 0.2 wt% Sc addition on the high temperature strength and microstructure evolution of Al-11.5 wt%Si-4.0 wt%Cu alloy in different states (as-cast, T6 and LTHE (long-time-heat-exposure at 300 degrees C for 100 h)) was studied in detail. Tensile test at RT (room temperature) and at 300 degrees C was used to examine the variation of strength. OM (optical microscope), SEM and TEM/HRTEM were used to characterize the microstructure. It is found that the value of sigma(0.2) (the yield strength) at 300 degrees C of the alloy with Sc-micro-alloying can be increased significantly, especially in T6 and LTHE states. During the ageing treatment, Sc-micro-alloying greatly increases the number densities of theta''; and theta' dispersoid particles, thus sigma(0.2) at 300 degrees Cof the samples in T6 state can be increased from 86 MPa to 116 MPa. By Elements-Mapping, it is found that Sc and Si co-exist inside theta' precipitates. This co-existence improves the thermo-stability of theta' phase and hence suppresses the coarsening behavior of theta' particles and phase transformation from theta' to theta during the LTHE treatment. Therefore, the value of sigma(0.2) at 300 degrees C of the alloy with Sc-micro-alloying in LTHE state still keep at a very high level of 99 MPa, with an increment of 36 MPa compared with the base alloy. (c) 2022 Elsevier B.V. All rights reserved.