Meaning
Solidification patterns create localized bands of alloying elements within a metallic matrix. Microsegregation stringers appear as visible lines of differing chemical composition under a microscope. These features form because certain elements solidify earlier than others in the melt.
The resulting heterogeneity can affect the mechanical performance of aluminium plates.
Solidification Path
Dendrites grow from the liquid phase and push solute atoms into the remaining fluid between the arms. This process creates microsegregation stringers when the final liquid freezes into thin streaks rich in iron or silicon. Rolling and extrusion then stretch these pockets into long directional features.
The orientation of these bands usually follows the direction of the manufacturing work. Molten metal must be carefully monitored.
Structural Weakness
Anisotropy introduced by these bands causes the metal to behave differently when loaded in various directions. Microsegregation stringers act as paths for crack propagation if they align with the principal stress. This might lead to failure during a crash.
Casting Control
Modification of the cooling rate and the use of grain refiners help to homogenize the material. Microsegregation stringers are minimized by ensuring a rapid and uniform transition from liquid to solid. Post-casting heat treatment can also help to diffuse the concentrated elements back into the matrix.
