Effect of multi-pass multi-directional forging on tribological properties of Si-rich eutectoid ZA alloys

The effect of multi-pass multi-directional forge (MDF) on the tribological properties of ZA22-xSi alloy (x=0, 4, 8 wt.%) was investigated. The results indicate that MDF breaks down the cast microstructure of alloys and produces a well-modified microstructure comprising finely distributed alpha- and eta-phases and primary Si particles. It is also found that, despite the matrix work softening, MDFed ZA22-xSi alloys show high wear resistance. The maximum wear resistance is observed in the five-pass MDFed ZA22-4Si sample, at the applied loads of 10 and 30 N, and its wear rates are lower than the wear rate of the as-cast ZA22 alloy by about 80% and 75%, respectively. MDF also significantly decreases both average friction coefficient and friction coefficient fluctuation of the sample. The high resistance of the substrate to microcracking, formation of hard Si reinforcements, fine redistribution of alpha- and eta-phases in the microstructure, and formation of tribolayers rich in Al and Zn oxides can be considered as the main factors improving the tribological properties.