Secondary Dendrite Arm Spacing
The secondary dendrite arm spacing is the distance between the side branches of a dendrite, which directly correlates with the local solidification rate and cooling rate.
Physical-Chemical Mechanism of Action
The secondary dendrite arm spacing (SDA) refers to the distance between the secondary branches of a dendrite. It is determined by the local solidification rate and the cooling rate. Fast cooling results in tighter spacing, slow cooling in wider spacing.
Metallurgical Relevance & Welding Risks
A too-large SDA can lead to a fine grain structure, which impairs the material's toughness and modulus of elasticity. A too-small SDA can result in a material that is too hard and prone to cracking, as it contains more glass-hard phases such as martensite.
Workshop Practice & Action Guidelines
To achieve the optimal secondary dendrite arm spacing, the cooling rate should be controlled. For high-carbon steels, slow cooling (e.g., with cooling water) is advisable to obtain a fine and ductile structure. For highly conductive metals like aluminum or copper, rapid cooling is necessary to avoid porosity.