A. Bahrami

An Age-Hardening Model for Al-Mg-Si Alloys Considering Needle-Shaped Precipitates

In the present study, an age-hardening model for Al-Mg-Si alloys was developed considering cylindrical morphology with constant aspect ratio for precipitates. It is assumed that the precipitate distribution during underaging is controlled by simultaneous nucleation and growth, and after peak age, the process becomes coarsening controlled. The transition from the nucleation/growth regime to the coarsening regime takes place when the equilibrium fraction of the precipitating phase is reached. The microstructural model is combined with a precipitation-strengthening model to predict the evolution of yield strength of Al-Mg-Si alloys during aging. The predictions of the model on the evolution of yield strength and length, radius, and volume fraction of precipitates are presented and compared with experimental data.

Toward a Recrystallized Microstructure in Extruded AA6005A Alloy

The correlation between extrusion processing parameters and chemical compositions on the one hand and the grain structure and mechanical properties on the other hand is studied for an extruded AA6005A alloy. Alloys with different chemical compositions and billet homogenization treatments have been extruded under different processing parameters. Optical microscope observations as well as hardness tests show that a wide range of mechanical properties and microstructures can be obtained. The grain structure can vary from a fibrous, deformed microstructure to a fully recrystallized micro structure. In some cases a mixture of the two is observed. The effects of processing parameters and chemical composition on the grain structure is discussed and used to find the optimized combination of homogenization treatment, pre-heating temperature, cooling rate after deformation, and chemical composition, in order to obtain a homogeneous recrystallized grain microstructure and optimum mechanical strength.