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Grain refinement

Problem statements

Large variations in grain refiner efficiencies Probably due to particle size distribution

Particle measurements

Grain refinement tests

Consensus on theory

Favourable growth conditions

Low levels of poisonous elements

High alloying

Titanium

Narrow particle size distribution

Optimization benefits

Underämne

Quality improvement - less amount of boride particles

Lower cost

Current usage

Average addition rate where Optifine is used is < 0.3 kg/t, i.e. 75 % less. If extended to whole consumption of grain refiners, 25 000 tonnes will propably suffice to grain refine all aluminium.

Annual consumption of 80 million tonnes of Al is grain refined with 100 000 tonnes of grain refiner = 1.25 kg/t

Growth

Type of alloying element

Strength of growth restriction factor

Phase diagram data. Element k m (k-1)m Ti 9 30.7 245 Si 0.14 -7.1 6.1 Mg 0.51 -6.2 3.0 Fe 0.02 -3 2.9 Cu 0.17 -3.4 2.8 Zn 0.4 -1.6 1.0 Mn 0.94 -1.6 0.1

Poisoning elements: Zr, Cr, (Mn)

Nucleation

Correlation particle size - undercooling

Particle size distribution

Type of nucleus

TiB2

TiC

Grain size optimization

Larger grain size in slabs - lower rolling forces? Will larger grain sizes in billets have benficial effects for extrusion?

What are the optimum grain sizes in various alloys in relation to casting processes, e.g. billet, slab, sheet etc. Much can be saved by enough grain refiner to obtain safe casts.

Enironmental aspects

Long transports from producer to user

KBF4 K2TiF6 Release of F2 to atmosphere Formation of HF