1. Dendritic stirring fracture theory
The core of the semi-solid billet is to generate non-dendritic equiaxed crystals, and the material is stirred in a semi-solid state. During the stirring process, the stirring force and speed are increased, and the shear force of the crystal grains is The impact from the liquid will also increase. When the force is greater than the strength limit of the crystal grain, the crystal grain will be broken, and the broken portion will be re-nucleated as a core to form a uniform equiaxed crystal structure.
2. Dendritic melting theory
During the agitation process, there is relative motion between the liquid, the agitation tool, and the crystal grains, and friction occurs, and heat is generated in the friction process. When the agitation is too intense, the heat may not be diffused, and local superheat may occur in the solid-liquid structure, causing the dendritic grains to partially melt and fall off, forming a new crystal nucleus and causing the formation of equiaxed grains.
3. Grain drift and mixed inhibition theory
When the alloy is stirred under electromagnetic action, the probability of grain fracture due to mechanical action is not large, and grain breakage is not the main reason for changing the grain nucleation condition. Under the strong agitation, the grains of the alloy will undergo large-scale movement and intergranular mixing. This phenomenon promotes the generation of non-uniform nucleation, resulting in more new crystals in the solid-liquid phase mixed structure. The core reduces the grain size, suppresses the anisotropy of the crystal grains, and causes the formed crystal grains to have a high roundness.