Effect of Zn content on the microstructure and mechanical properties of as-cast Al–Zn–Mg–Cu alloy with medium Zn content

Abstract

The as-cast Al–Zn–Mg–Cu alloys with different Zn content were prepared by metal gravity casting. The microstructure and constituent phase of the different alloys were examined by optical microscope, scanning electron microscope, energy-dispersive X-ray spectroscopy, inductively coupled plasma spectrometer and X-ray diffraction. The increase of Zn content caused the changes of the morphology and size of α-Al matrix dendrites and the intergranular eutectic structure, but it did not affect the constituent phases of the alloys. The morphology changes of the α-Al matrix dendrite and strengthening phase lead to different changes in the mechanical properties of the alloy. With the increase of Zn content, the ultimate tensile strength gradually enhance to the maximum value of 248.05 MPa; the yield strength remained relative stable at 179.39 ± 6.81 MPa. The elongation obviously increases first and then decreases, but the Brinell hardness is the opposite. The alloy with a Zn 5.8 wt.% has a minimum Brinell hardness of 74.40 HBW and a maximum Elongation of 8.78%. The transformation of fracture mode caused by the change of Zn content leads to the change of plasticity.