The effect of Ti-B and Sr on the mechanical behaviour of the zinc-aluminum-based ZA-12 alloy produced by gravity casting

Abstract

In this study, the effect of Ti-B (0.05-0.7 wt.% Ti, 0.01 - 0.13 wt.% B) and Sr additions (0.05-0.7 wt.%) on the hardness, ultimate tensile strength (UTS), strain and fatigue properties of the gravity cast Zn-Al-based ZA-12 alloy was investigated. While the Ti-B additions had no significant effect on the hardness of the alloys, the Sr additions lowered the hardness by a small amount. UTS and fatigue resistance of the ZA-12 alloy increased with 0.05 wt.% Ti, but the addition of 0.05 wt.% Sr to the standard alloy did not change these properties significantly. In excess of 0.05 wt.% Ti and Sr, the UTS and fatigue resistance of the alloys decreased and reached a lower value than that of the standard alloy. The failure strain only increased for the ZA-12 alloy containing 0.05 wt.% Ti, then decreased with further increase in Ti content. The failure strain values of the alloys decreased with addition of Sr. Metallographic examination indicated that the addition of Ti-B strongly modified the microstructure of the standard ZA-12 alloy, but Sr did not. Ti and Sr have also formed complex-shaped intermetallic compounds, which were identified as Al5Ti2Zn and Zn5Al3Sr by X-ray diffraction and EDS analyses. It can be suggested that these particles cause a decrease in UTS, fatigue resistance, and strain to failure of the ZA-12 alloy.