Correlation between solid fraction and tensile properties of semisolid RAP processed aluminum alloys

Abstract

Recrystallization and remelting (RAP), a promising route for thixoforming process, was used to process three aluminum alloys, AA2024, AA6061, and A356, under experimental conditions designed to yield various solid fractions (liquid fractions) within the microstructure. The thixotropic microstructures obtained were characterized in detail and linked to the corresponding tensile properties. When the liquid fraction increased (the solid fraction decreased), an initial reduction in the tensile properties was perceived. The lowest tensile properties were obtained at liquid fractions of 35% (610 °C), 25% (623 °C), and 40% (585 °C) for AA2024, AA6061, and A356 alloys, respectively. For the AA6061 and A356 alloys, a further increase in the liquid fraction resulted in improvement of the tensile properties. However, for the AA2024 alloy, the samples could not withstand their own weight at higher liquid fractions that further tensile tests were rendered. It was concluded that for alloys below the liquid fraction corresponding to the minimum tensile properties, the structural properties of interconnected grains (skeletons), and the quenched liquid eutectic phase located at the grain boundaries (liquid film) controlled the fracture behavior. Nevertheless, the nature of the cohesion between the grains and the liquid film was the determining factor in the improvement in the tensile properties that resulted when the liquid fraction was increased to 46% and 60% for the AA6061 and A356 alloys, respectively.