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.