Microstructural evaluation and mechanical properties of 7075 aluminum alloy prepared by controlled diffusion solidification

In the present work, 7075 aluminum alloy (Al-Zn-Mg-Cu) was produced by both conventional casting (CC) and controlled diffusion solidification (CDS) methods. Each sample was subjected to different heat-treatment conditions: as-cast, T4, and T6; and their microstructural and mechanical properties were investigated by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffractometry (XRD). It was found that CDS promoted the formation of non-dendritic primary α-Al phase and reduced shrinkage porosity, thus resulting in improved mechanical properties. In addition, the eutectic phase of the CDS samples mainly consisted of T(Al-Zn-Mg-Cu) phase, which manifested a well-developed lamellar eutectic structure. However, in the CC samples, the T(Al-Zn-Mg-Cu) phase was composed of rod-like eutectics. Moreover, the θ(Al2Cu) eutectic contents in the CC samples were greater than those in the CDS samples. Each element in the CC samples had an obvious change in the grain boundary, whereas the change in element content in the CDS samples was gradual. Therefore, the non-dendritic morphology of the primary phase and the presence of rod-like eutectics in the matrix of the CDS samples led to enhanced tensile strength and elongation under different heat treatment conditions.