Effect of Melt Treatment on Microstructure Evolution and Coarsening Mechanism of A356 Al Alloy During Cooling Slope Rheoprocessing

The present study reports the effect of melt treatment, i.e., grain refiner (0.15 wt pct of Al-5Ti-1B) and modifier (0.1 wt pct of Al-10Sr) addition on microstructure formation mechanism of A356 Al alloy, processed at semi-solid state. The semi-solid processing is performed here adopting rheoprocessing route, which involves cooling slope processing and subsequent isothermal holding of the generated slurry. Melt treatment prior to slurry generation shows pronounced effect over the morphology of primary solid (Al) and eutectic Si particles, and to quantify that, shape and size of both the particle types are measured in the present work. Moreover, based on the insight obtained in the present study, possible slurry microstructure formation mechanisms, at the onset of melt treatment, are proposed. Furthermore, mathematical model of primary Al formation and its coarsening is developed within the scope of the present work, based on the experimental findings. Understanding of microstructure formation mechanism as well as the developed mathematical correlations between process variables and slurry morphology are found to be helpful to establish process control during Rheo pressure die casting of the generated slurry, to develop automobile, aviation components. [GRAPHICS] .

Automated summary

The present study investigates the impact of melt treatment on the microstructure formation mechanism of A356 Al alloy in the semi-solid state. The addition of a grain refiner and modifier significantly influences the morphology of primary solid Al and eutectic Si particles. Possible mechanisms for slurry microstructure formation during the onset of melt treatment are proposed, and a mathematical model for the formation and coarsening of primary Al is developed based on experimental findings. Understanding the microstructure formation mechanism and establishing mathematical correlations between process variables and slurry morphology are important for process control in Rheo pressure die casting and the development of automobile and aviation components.