Disagglomeration in thixoformed wrought aluminium alloy 2014

Thixoforming is a type of semi-solid metal processing, which involves the processing of alloys in the semi-solid state. Disagglomeration of solid globules during thixoforming of wrought aluminium alloy 2014 was investigated by electron back-scatter diffraction. The recrystallisation and partial melting route was used to produce the thixotropic feedstock for thixoforming. The starting material was commercially extruded wrought aluminium alloy 2014 in the T6 temper condition. The crystallographic orientations of the grains and misorientation between neighbouring grains were investigated in the starting material, isothermally heat-treated material (heat treated at temperatures up to 901 K to mimic the treatment which the thixoformed sample undergoes prior to forming) and in as-thixoformed material. The starting material showed strong {1 1 0}〈3 2 2〉 and {1 1 2}〈1 1 1〉 components, which were replaced by strong {1 0 0}〈0 0 1〉 texture during heat treatment. Thixoforming of the material almost completely randomised the texture, indicating that disagglomeration has occurred. About a quarter of the boundaries in the as-received material are low angle grain boundaries. This declines to about 18% in the heat-treated but the as-thixoformed misorientation data suggests a very high proportion of LAGBs. This is thought to be an artefact associated with the fact that the EBSD programme is attempting to resolve the microstructure within what was liquid and to allocate orientations within that. The data do not represent the parameter which is sought viz. the misorientation between what were neighbouring solid spheroids in the semi solid state because these are now separated by solidified liquid. The data on misorientation in systems which have been semi-solid must therefore, be treated with circumspection.