Hot formability and microstructural development of spray-deposited Al-Li alloy and composite.

The deformational and microstructural behaviour of the commercial Al-Li alloy 8090 and
an 8090 based composite containing silicon carbide particulate has been investigated.
The materials were deformed at elevated temperature by the test methods of plane strain
compression (PSC) and torsion to provide stress-strain data for the formulation of constitutive
relationships. Torsion testing also provided high temperature ductility data. Isothermal annealing
of rolled samples was carried out at the solution temperature of 530°C to investigate the
recrystallisation kinetics and microstructures produced, with particular emphasis on the effect of
the inclusion of reinforcement particles on the behaviour of the matrix alloy.
Hyperbolic sine forms of constitutive equation have been produced and are found to provide
good agreement with the experimental data. High values of the activation energy are calculated
for the deformation of both the alloy and composite from the PSC test data.
The equations obtained from the two different test methods are found to be comparable for
the composite material, but a discrepancy is found for the monolithic alloy, where apparently less
hardening results from torsion testing.
A distinct transition in microstructure from recrystallised equiaxed grains when deformed
at low temperature to an elongated, sometimes partially recrystallised, structure for material rolled
at high temperature is present in the monolithic material. This is attributed to the balance of
recrystallisation driving force and the Zener pinning force exerted by the 13' (A1 3Zr) phase.
The composite material exhibited greatly enhanced recrystallisation kinetics in agreement
with the theory of particle stimulated nucleation (PSN) of recrystallisation.