Effect of intermediate processing treatment on the structure and mechanical properties of Al–4 wt%Cu–3 wt%Mn alloy manufactured by electromagnetic casting followed by high-pressure torsion (HPT)

Abstract

In this work, a thermally stable model Al–4Cu–3Mn (wt%) alloy has been manufactured by electromagnetic casting (EMC), followed by compression, intermediate heat treatment and high-pressure torsion (HPT). Structural changes of the alloy during subsequent processing stages have been analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the X-ray diffraction (XRD). The results indicate that variations in the intermediate heat treatment temperature of the compressed samples lead to a significant difference in strain hardening and thermal stability after HPT. According to microstructure investigations the hardening of samples processed by HPT resulted from formation of mixture of grains and subgrains with high dislocation density as well as mechanical fragmentation of eutectic Al2Cu particles and precipitation of nanoscale Mn-rich dispersoids which are identified as Al6Mn. The intermediate heat treatment of the EMC rod at 350 ºC for 3 hours and heat treatment of HPT sample at 250 ºC for 5 hours exhibited the best mechanical properties in terms of ultimate tensile strength (UTS), yield strength (YS) and elongation (El), reaching 610 MPa, 560 MPa and 10 % respectively. At the same time intermediate annealing at 450 °C makes the HPT processing ineffective.