Tribology characteristics of novel Zn–Si alloys severely deformed by multi-directional forging

Multi-pass multi-directional forging (MDF) was applied to enhance tribological properties of Zn–4Si alloy. According to the results, MDF effectively refined coarse irregular-shaped primary Si particles (PSPs) and encouraged their uniform distribution within the matrix. MDF also modified the microstructure by forging porosities and eliminating entrained bifilm oxides. The average size of PSPs and volume percentage of porosities decreased from 38.7 ± 11.5 μm and 0.82 ± 0.17% in the as-cast sample to 6.8 ± 3.1 μm and 0.19 ± 0.05% in the 8-pass MDFed sample, respectively. The maximum hardness was obtained in a 4-pass MDFed sample where its hardness was increased from 37.8 ± 3.2 in as-cast state to 52.7 ± 1.1 HB. The 4-pass MDFed sample also showed the maximum wear resistance where at applied pressures of 0.25, 0.5, and 0.75 MPa, its wear rate was lower than that of the as-cast sample by 83, 76, and 72%, respectively. MDFed samples also exhibited improved friction properties. At the applied pressures of 0.25, 0.5, and 0.75 MPa, the friction coefficient of the 4-pass MDFed alloy was lower than that of the as-cast alloy by 38%, 29% and 20%, respectively.