Structure evolution and compressive behavior of semi-solid Al–Si hypoeutectic alloy with re-melting heat treatment

This paper presents a new method—a re-melting heat treatment method—to fabricate a semi-solid billet of Al–Si hypoeutectic alloy and examines the effect of re-melting temperature, holding temperature and holding time on the semi-solid structural evolution. Semi-solid compression tests are carried out to investigate the deformation behavior and deformation mechanism using a semi-solid billet fabricated by the re-melting heat treatment method. Semi-solid compressive deformation is described using a simple hexagon model. In the compression forming of a semi-solid billet the liquid flow leads to motion or rotation of solid particles, which results in the appearing of some “vacancy” among the primary phase. This makes it easy for solid particles nearby to move to the position of “vacancy” to reach a new arrangement. Semi-solid compressive deformation involves liquid flow, motion or rotation and plastic deformation of solid particles. The solid fraction will affect the practical deformation manner. For a low solid fraction the rotation or motion of solid particles and liquid flow will take a dominant role, whilst for a high solid fraction the solid particles tend to contact each other, so that plastic deformation of solid particles is the main manner. This compressive deformation model is verified by experimental results.