THE COARSENING OF SILICON PARTICLES IN A SUBMICRON-GRAINED LAYER-DEPOSITED AL-12WT-PERCENT-SI ALLOY

A submicron-grained Al-12wt%Si alloy with a uniform distribution of fi ne silicon particles was produced by a layer-deposition process and su bsequent hot working. The grain structure was characterized by high an gle grain boundaries with a random spectrum of orientation. The averag e sizes of both grain and silicon particle were about 0.4mum in the as -rolled state. The grain refinement came from the dynamic recrystalliz ation on silicon particles. The grains did not show significant growth in annealing even at 496-degrees-C for 24 hours, whereas silicon part icles grew at a remarkable rate. The coarsening phenomenon of silicon particles at elevated temperatures was studied systematically by annea ling the specimens at 372-degrees-C, 433-degrees-C, 472-degrees-C and 493-degrees-C respectively for different periods. Results showed that the volume of a silicon particle increased linearly with annealing tim e. The activation energy for coarsening was calculated by Arrhenius eq uation to be 54 kcal/mole which is almost triple the activation energy for silicon diffusion in aluminium matrix. Because of the high energy value, the coarsening should not be diffusion-controlled but interfac e-controlled. In addition, the size distribution profile of silicon pa rticles in aluminum matrix after annealing also accounts for the inter face-controlled kinetics.