Effect of grain refinement with titanium on the microstructure, mechanical and corrosion properties of Al-25Zn alloy

Abstract

In this study, one binary Al-25n alloys and eleven ternary aluminum-zinc-titanium alloys, Al-25Zn-0.01Ti, Al-25Zn-0.03Ti, Al-25Zn-0.04Ti, Al-25Zn-0.05Ti, Al-25Zn-0.075Ti, Al-25Zn-0.1Ti, Al-25Zn-0.2Ti, Al-25Zn-0.4Ti, Al-25Zn-0.6Ti, Al-25Zn-0.8Ti and Al-25Zn-1Ti, were produced by permanent mold casting method. Structural, mechanical, and corrosion properties of the tested alloys were investigated. Structural investigations were carried out with scanning electron microscope (SEM) and X-ray diffraction (XRD) studies. Mechanical properties of the alloys were determined with the Brinell hardness and tensile tests. Corrosion tests were carried out with electrochemical test setup in accordance with ASTM G5 standard. Al-25Zn and Al-25Zn-Ti alloys were composed of α and η phases as the main matrix, and it was observed that Al3Ti phase began to precipitate in the microstructure when the titanium content exceeded 0.01%. In addition, the size of dendrites or grains of the Al-25Zn-Ti alloys was found to be much smaller than that of binary alloy. The hardness, yield strength, and tensile strength values of the Al-25Zn alloy significantly increased with the 0.01%Ti addition, but when Ti content exceeded 0.01%, these values decreased with increasing titanium content. It was observed that titanium addition had a negative effect on the corrosion properties of the Al-25Zn alloy. The change on the mechanical and corrosion properties of the Al-25Zn alloy due to the titanium addition in different ratios have been explained based on the structural properties of the alloys.