Modelling precipitation hardening in an A356+0.5 wt%Cu cast aluminum alloy

The behavior of a A356+0.5 wt%Cu alloy used to manufacture cylinder heads was studied. Samples were solutionized, quenched and aged at 200 degrees C for 0.1, 1, 10 and 100 h. TEM characterization showed that for the short aging durations (up to 10 h), the dominating hardening precipitates were beta '' rods, while for the long aging duration (100 h), the dominance shifted to the Q-phase (Q ', Q '' precipitates). The length and diameter of the beta '' rods were measured to produce size distributions which were later used to calibrate and validate the precipitation model. The physics-based precipitation kinetics model relies on classical nucleation/growth/coarsening equations adapted for the precipitation of Mg-Si precipitates in the aluminum matrix. Indirect coupling to Thermo-Calc software was used in order to determine the essential thermodynamic variables such as the driving force for precipitation and the solubility product for the model. Recent developments regarding the correction of the growth rate equations and the curvature effect were used to take into account the elongated morphology of precipitates. A Kampmann-Wagner Numerical (KWN) based model was used to track the evolution of the size distributions during nucleation, growth and coarsening of the beta precipitates. The yield strength of the alloy was modelled using the Pythagorean sum of the contributions of intrinsic strength, solid solution strengthening and precipitation hardening. Both models showed good accuracy when compared to experimental results.

Automated summary

The behavior of a A356+0.5 wt%Cu alloy used to manufacture cylinder heads was studied. Samples were solutionized, quenched and aged at 200 degrees C for different durations. The dominance of different precipitates at various aging durations was observed and validated using TEM characterization. The physics-based precipitation kinetics model showed good accuracy in predicting the yield strength of the alloy, with recent developments in growth rate equations and curvature effects taken into account.