Influence of Al3Ni crystallisation origin particles on hot deformation behaviour of aluminium based alloys

Binary Al-Ni, Al-Mg and ternary Al-Mg-Ni alloys containing various dispersions and volume fraction of second-phase particles of crystallisation origin were compressed in a temperature range of 200-500 degrees C and at strain rates of 0.1, 1, 10, 30 s(-1) using the Gleeble 3800 thermomechanical simulator. Verification of axisymmetric compression tests was made by finite-element modelling. Constitutive models of hot deformation were constructed and effective activation energy of hot deformation was determined. It was found that the flow stress is lowered by decreasing the Al3Ni particle size in case of a low 0.03 volume fraction of particles in binary Al-Ni alloys. Intensive softening at large strains was achieved in the alloy with a 0.1 volume fraction of fine Al3Ni particles. Microstructure investigations confirmed that softening is a result of the dynamic restoration processes which were accelerated by fine particles. In contrast, the size of the particles had no influence on the flow stress of ternary Al-Mg-Ni alloy due to significant work hardening of the aluminium solid solution. Atoms of Mg in the aluminium solid solution significantly affect the deformation process and lead to the growth of the effective activation energy from 130-150 kJ/mol in the binary Al-Ni alloys to 170-190 kJ/mol in the ternary Al-Mg-Ni alloy.