Microstructural evolution and rheological properties of AA6063 alloy produced by semisolid processing (SIMA and MHD)

In this work the theological behaviour and the microstructural evolution of alloy AA6063 submitted to two different processing routes were studied: cold deformation and partial fusion (SIMA process) and magneto hydrodynamic stirring during its solidification (MHD process). The microstructural evolution during the isothermal holding was studied to verify if the Ostwald ripening mechanisms, classic growth and coalescence, are applicable to alloys made by these processing routes. The rheological properties were evaluated using a compression rheometer with parallel plates and digital capture of position and time data. Compression tests were made in short cylinders extracted from ingots that showed: a dendritic microstructure typical of as cast material, a typical microstructure of cold deformed material and a microstructure of materials obtained by MHD process. It was found that a globular microstructure has a typical behaviour of a fluid when being formed in semisolid state, contrary to the behaviour of the as cast dendritic microstructure. In addition, the mechanisms that operate in the microstructural evolution during the isothermal holdings were verified, through metallographic analysis.