The utilization of cast aluminum alloys in automotive industry continues to rise because of consumer demand for a future generation of vehicles that will offer excellent fuel efficiency and emissions reduction, without compromising safety, performance, or comfort. Unlike wrought aluminum alloys, the cutting speed for cast aluminum alloys is considerably restricted due to the detrimental effect of the alloy’s silicon constituencies on tool life. In the present study, a new wear model is developed for tool-life management and enhancement, in a high-speed machining environment. The fracture-mechanics-based model requires normal and tangential stresses, acting on the flank of the cutting tool, as input data. Analysis of the subsurface crack propagation in the cobalt binder of cemented carbide cutting tool material is performed using a finite element (FE) model of the tool-workpiece sliding contact. The real microstructure of cemented carbide is incorporated into the FE model, and elastic-plastic properties of cobalt, defined by continuum theory of crystal plasticity are introduced. The estimation of the crack propagation rate is then used to predict the wear rate of the cutting tool. The model allows the microstructural characteristics of the cutting tool and workpiece material, as well as the tool’s loading conditions to be taken into consideration. Analysis of the results indicates that the interaction between the alloy’s hard silicon particles and the surface of the cutting tool is most detrimental to tool life. The fatigue wear of the cutting tool is shown to be directly proportional to the silicon content of the alloy, silicon grain size, and to the tool’s loading conditions.