Al-Cu System: Phase Stability and Aging Effects

This lecture discusses the Al-Cu alloy system, focusing on the phase stability and the effects of aging on mechanical properties. It begins with an overview of the precipitation process at low temperatures, where less stable precipitates can form first and persist until more stable phases appear. The instructor presents a detailed time-temperature-transformation (TTT) diagram for the Al-4 wt% Cu alloy, emphasizing that peak strength is achieved through aging at lower temperatures for extended periods. The formation of GP zones is highlighted, noting that they do not develop above 180 °C, which is critical for achieving optimal yield strength. The lecture also covers the implications of copper content in the alpha phase and the significance of the eutectic composition during solidification. The instructor provides insights into the thermodynamic principles governing the solidification process and the maturation of microstructures in aluminum alloys, illustrating these concepts with diagrams and examples from engineering materials literature.