The Influence of Particles Introduced Into the Melt on Grain Refinement in the Final Structure of Aluminum Alloys

The results of an experimental investigation performed in this study allow supposing that a change in the aggregate state (crystallization) of a substance on the surface of the introduced small-sized (nano- or submicron) particles significantly affects the grain size in the final states of the alloys and composites. This is due to the fact that the melt – particle system is found in a low-stability state, hence even weak thermal actions of the inoculators-microparticles can influence the final state of the alloy, both its structure and physical-mechanical properties. As a result of thermal interaction between the particle and the melt, whose temperature is close to that of the change of the aggregate state (crystallization), the metal on the surface of the particle changes its aggregate state. A thermal model of the change of the aggregate state of a substance proposed in this study makes it possible to predict the velocity and degree of local cooling of the melt, the crystallization time, and the minimal size of the resulting crystallites as a function of the particle dispersion and mass concentration. The smaller the size of the particles and the higher their mass concentration, the smaller the grain size in the final alloy. The full-scale experiment verified the principles obtained in the thermal model: the smaller the size of introduced particles, the smaller the grain size of the final alloy. The average grain size of the initial technical-grade aluminum was ~1200 μm. Upon introduction of 0.2 wt.% of composite SHS-master alloys of the Al–Ti–B4C system (average particle size 0.4 μm) the average grain size of the alloy was found to be 410 μm. Upon introduction of 0.2 wt.% of composite SHS-master alloys of the Al–Ti–B system (average particle size 0.7 μm) the average grain size of the alloy was found to be 540 μm.