Structural characteristics, mechanical behaviour and damping properties of Ni modified high zinc Al-Zn alloys

The microstructure, mechanical behaviour and damping properties of two high zinc Al-Zn alloys -Al-20Zn and Al-35Zn alloys - micro alloyed with 0.1, 0.2, and 0.3 wt% Ni were investigated in this study. The alloys were produced by liquid metallurgy processing using metal casting practice. The structural characteristics of the alloys were assessed using scanning electron microscopy and x-ray diffraction analysis while the mechanical properties (hardness, tensile properties and fracture toughness) and damping behaviour were also evaluated. The results show that the Al-35Zn alloys generally have finer grain sizes compared with the Al-20Zn alloys, while the use of 0.1 wt%Ni, resulted in the most significant grain size reduction. The hardness and tensile strength improved with the use of 0.1 and 0.2 wt% Ni for the Al-20Zn and Al-35Zn alloys, and strengthening was largely higher for the Al-35Zn alloys than the Al-20Zn alloys due to finer grain size and the greater proportion of the Zn rich η- phase. The percent elongation and fracture toughness improved with Ni addition in both Al-20Zn and Al-35Zn base alloys, but the use of up to 0.3 wt% Ni in some instance resulted in marginal improvement in both properties. Also, the use of 0.1 wt% Ni resulted in the most significant improvement in damping capacity for both high zinc Al-Zn alloys. Summarily, the use of 0.1-0.2 wt% Ni as micro alloying addition in Al-20Zn and Al35Zn base alloys resulted in improved strength, ductility, toughness and damping capacity in the alloys.