Role of Zn addition in tailoring the microstructure, mechanical properties, and corrosion resistance of Al–4 wt%Cu Alloy

Aluminum alloys are widely used in the automotive industry because of their lightweight and excellent corrosion properties. This study investigated the effect of Zn addition (3 wt%, 5 wt%, and 7 wt%) on the microstructure, mechanical properties, and corrosion behavior of an Al-4 wt%Cu alloy. The sand-casting process prepared the alloy samples, and the raw materials were melted at 740–750℃ . Al-4 wt% Cu alloy is used as a base alloy because it provides optimal tensile strength and impact energy, and exhibits less brittle behavior compared to aluminum alloys. Increasing the Zn percentage on Al-4wt%Cu alloy enhances the tensile and yield strength due to the formation of finer intermetallic phases such as Al 2 Cu, CuZn 5 , Al 82 Zn 17, and Al 4 Cu 3 Zn, which hinder dislocation movement and refine the grain boundary. However, this study observed that elongation initially decreased at 3 wt% Zn compared to the base alloy but progressively increased with further Zn addition to 5 wt% and 7 wt% in Al-Cu alloy but decreased the hardness value. The study found that 7 wt% Zn added to Al-4wt% Cu alloy showed better ductility and tensile strength (with 163 MPa) compared to the base alloy (of 83 MPa). However, 3 wt% Zn added to the Al-Cu alloy showed the lowest tensile strength and brittle material due to coarser intermetallic phases and larger grain boundaries. The optical microscope and SEM images revealed the presence of coarser intermetallic phases and larger grain boundaries. The EDS analysis confirmed the presence of Al, Cu, and Zn elements and globular intermetallic phases. XRD analysis confirmed the elements present in different crystallographic planes and also demonstrated that increasing the zinc percentage decreases the peak intensity due to lattice distortion. Corrosion resistance exhibited a non-monotonic trend, with the best performance at 5 wt% Zn, whereas further increasing the Zn content to 7 wt% significantly deteriorated the corrosion performance.