Effects of Cu and Ti Contents on Microstructure and Properties of Al-8.8Zn-2.2Mg-xCu-0.2Zr-0.1Sr-yTi Aluminum Alloy

Al-8.8Zn-2.2Mg-xCu-0.2Zr-0.1Sr-yTi aluminum alloys (AAs) with the different Cu and Ti contents were self-designed and fabricated by melting, casting and extrusion techniques, which were aged by T6 process. The microstructure and intergranular morphologies of obtained AAs were observed using an optical microscope (OM). The morphologies of AAs after intergranular corrosion were investigated using a scanning electron microscope (SEM), and their chemical composition and dislocation enhancement were analyzed using an energy-dispersive spectrometer (EDS) and x-ray diffraction (XRD), respectively. The hardness and electrical conductivity of AAs were measured using a Vickers hardness and eddy current conductivity testers, respectively, and the tensile properties were investigated using a drawing machine. The results show that the addition of Ti refines the grains of AAs, which inhibits the recrystallization and improves the hardness, tensile strength, and corrosion performance. Moreover, the excessive Cu content suppresses the grain refinement effect of Ti, which decreases the tensile strength of AAs. The high Cu content in the AAs generates coarse and brittle phases to decrease the plasticity and electron scattering of AAs, resulting in the enhancement of electrical conductivity.