Effects of applied pressure and residual heat quenching on the mechanical and thermal properties of cast Al–Mg–Zn–Mn–Fe alloys

In this study, the effects of applied pressure (AP) and residual heat quenching (RQ) on the mechanical properties and thermal conductivities of Al-4.6Mg-3.6Zn-0.86Mn-0.48Fe alloys were investigated based on intensively microstructure analysis by scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM) and synchrotron X-ray tomography (SXT). The results indicated that AP and RQ did not change the type of intermetallic; instead, they reduced the length and quantity of lath-like Al6(Fe,Mn) and significantly refined the grain by increasing the cooling rate. Moreover, η′ precipitation particles were enriched near the grain boundaries, which was beneficial for the yield strength of the alloy; the AP + RQ sample exhibited the best mechanical properties of the ultimate tensile strength, yield strength and elongation of 269 MPa, 164 MPa and 11.4 %, respectively, which were 19 %, 17 %, and 83.8 % higher than those of the gravity cast (GC) sample. Moreover, the thermal conductivity of the AP + RQ sample did not show significant changes, which were attributed to the reduction in solid solute caused by the increased volume fraction of η′ precipitates, thus improving the thermal conductivity; however, the formation of numerous semi-coherent interfaces between η′ and the matrix led to increased lattice distortion, resulting in electron scattering.