Structural, mechanical and tribological characterization of Zn25Al alloys with Si and Sr addition

• Influence of the strontium (Sr) addition on the Zn25Al–Si alloys were investigated.
• The microstructure was improved upon the addition of strontium.
• The hardness and compressive yield stress did not change significantly.
• The wear resistance was improved, and coefficient of friction was slightly increased.
• The increase in wt.% Sr showed an effect of a double-nature on the wear resistance.

The ZA-27 alloy is a zinc–aluminium casting alloy that has been frequently used as the material for sleeves of plain bearings. It has good physical, mechanical and tribological properties. However, one of the major disadvantages is its dimensional instability over a period of time (ageing). To overcome this, copper in the alloy may be replaced with silicon. Coarsening of silicon particles can be controlled by a suitable addition of strontium. In this paper, the commercial ZA-27 alloy and six different Zn25Al alloys (with 1 and 3 wt.% silicon; and with 0, 0.03 and 0.05 wt.% strontium) were obtained by casting in the preheated steel mould. Casting of the alloys was carried out at a laboratory level. In the alloys containing silicon, a finer dendritic structure was noticed compared to the structure of the commercial ZA-27 alloy. The addition of strontium influenced the size and distribution of primary silicon particles. Needle-like particles of eutectic silicon were changed into the fibrous ones. The presence of silicon and strontium did not significantly affect mechanical properties of the obtained Zn25Al alloys compared to mechanical properties of the commercial ZA-27 alloy. Wear rate of the alloys containing silicon was lower than that of the ZA-27 alloy. The addition of strontium further lowers the wear rate and slightly increases the coefficient of friction.