Microstructural evolution and mechanical properties of the semisolid Al-4Cu-Mg alloy

Microstructural evolution and the mechanical properties of the semisolid Al-4Cu-Mg alloy were investigated, and a grain coarsening equation of this semisolid alloy in the semisolid state was provided based on Ostwald ripening theory. The experimental results showed that the process parameters, including height reduction, isothermal temperature and holding time, affect grain size, fractal dimension and distribution of grain size to some extent. The grain size decreases with an increase of the height reduction, a decrease of the isothermal temperature and/or the holding time. The spheroidization of grains is promoted with an increase of height reduction, isothermal temperature or holding time. The grain size has a Gaussian distribution under different experimental conditions. There will be a more uniform distribution of grain size at high height reduction, low isothermal temperature and short holding time. The pretreatment of samples with cold or hot deformation before isothermal heat treatment is necessary. Good ultimate strength and yield strength could be obtained by the conditions of suitable height reduction, low isothermal temperature and short holding time. Finally, a kinetic equation of grain coarsening was put forward, which could be applied to the semisolid Al-4Cu-Mg alloy system over a high volume fraction of separated grains range from 0.75 to 0.90.