Selection of Dedicated As-Cast Microstructures in Zn-Al-Cu Alloys for Bearing Applications Supported by Phase-Field Simulations

Solidification and phase formation of Zn-rich Zn-Al-Cu alloys with different Al and Cu contents were investigated. The investigations comprise alloy compositions with either hcp eta, fcc alpha or hcp epsilon as the primary phase, as well as a composition close to the ternary eutectic point. Test samples were produced in a mold casting process and their microstructures were investigated by scanning electron microscopy. Experimental microstructures are compared with the results from spatially resolved microstructure simulations using a phase-field model. In particular, the dependency between the aluminum and copper contents and the phase fractions of the eta, alpha and epsilon phases were analyzed. In addition, hardness tests for the samples prove a direct correlation between the alpha- and epsilon-phase fractions with the macroscopic hardness of the alloys. A simple model, based on the phase fractions and the properties of the single phases, is suggested for the computation of hardness from the simulation results in order to select appropriate alloy compositions for bearing applications.