Dendritic arm spacing
The characteristic distance between primary or secondary arms of solidifying dendrites, directly dependent on the local cooling rate and determining microstructural fineness.
The dendrite arm spacing forms during solidification of the melt and largely determines the fineness of the structure. The smaller the spacing, the finer the structure and, as a rule, the better the strength and toughness. In practice, you mainly control this via the cooling rate. Rapid cooling gives fine dendrites, slow cooling gives coarse ones. A too coarse structure makes the material brittle and prone to cracking. So make sure there is controlled heat dissipation, especially with thick parts or when you have high toughness requirements. Too much heat in the part is the most common mistake – then the grain becomes coarse and the weld suffers.