Utilisation of atom probe data to model precipitation and strengthening in an Al-Mg-Si-Cu alloy during natural ageing and early-stage artificial ageing

An Al-Mg-Si-Cu alloy was artificially aged for 0.13, 0.5 or 2 hours at 170°C after natural ageing times of 0.03, 3 or 168 hours. Three dimensional atom probe (3DAP) analysis and tensile testing were performed in the artificially aged and naturally aged conditions. The experimental data were used to determine model inputs such as particle size distributions and volume fractions of particles. The principle of the model is to numerically simulate the isothermal transformation of clusters, zones and/or precipitates by dividing the starting particle distribution into a series of discrete size classes and control volumes. Standard physically-based equations are used to simulate particle growth and/or dissolution by adjusting enthalpy, entropy and interfacial energy values to obtain a good fit between model predictions and 3DAP results. The predicted particle size distributions and volume fractions are then used to model yield strengths in a wide range of naturally aged and under-aged conditions.