When aluminium is cast into billets or slabs, alloying elements segregate and coarse intermetallic phases form at grain boundaries. Homogenisation heats the cast metal to a high temperature below its melting range, holds it for several hours, and then cools it at a controlled rate. In 6xxx billets such as 6063, this dissolves coarse Mg2Si, transforms needle-like iron phases into rounder forms, and leaves a structure that deforms evenly.
Why it matters when buying
- Properly homogenised billet extrudes faster with less pressure, and gives better surface finish and more consistent response to ageing and anodising.
- Unhomogenised or poorly homogenised billet can cause surface streaks, tearing and die wear in extrusion.
- Ask the supplier to confirm homogenisation on the certificate, and whether it is done in-house or by a contractor.
- Cooling rate after soaking matters as much as the soak itself; uneven cooling gives variable results along the billet.
Notes
Rolling slab is also homogenised (often called preheating) before hot rolling. See listings under billets and wire rod.