Semi-solid compression of 2A14 alloy with high solid fraction: rheology, constitutive equation and microstructure

In this paper, semi-solid compression of 2A14 aluminum alloy was conducted on the Gleeble1500D thermophysical simulation experimental compressor to investigate the rheological behavior of 2A14 alloy at high solid fraction in the semi-solid state. The main objective of the study was to establish the constitutive equation suitable for serving the simulation and practical thixoforging forming process of the 2A14 alloy. Another purpose is to investigate the effect of heat deformation parameters on the microstructure of 2A14 alloy. The apparent viscosity of semi-solid 2A14 alloy with high solid fraction as a function of equivalent shear rate was obtained. The constitutive equation for 2A14 aluminum alloy at true strain below 0.2 was established. Increasing the compression temperature or strain rate is beneficial to the deformation and grain refinement in the hard deformation zone, but at the same time, it will also intensify the aggregation of micro-voids in the transition zone into micro-cracks and the formation of macro-cracks. The macroscopic compression instability at true strains above 0.2 was discussed, mainly attributed to the dilatant shear bands generated in the strain localization region inherent in the compression deformation and the higher thermal crack sensitivity of the 2A14 alloy.