Semi–solid squeeze–forming of A356 aluminium alloy with dendritic and non–dendritic structures

In this study, the main mechanism for producing the non–dendritic structure is deforming of the dendrite arms due to shearing force. The semi–solid flow is mainly a laminar flow, rather than the turbulent flow. The gas porosity and shrinkage porosity are absent in the specimens. The flowability of the non–dendritic primary particles is much better than that of the dendritic solid phase. The non–dendritic primary particles in the squeeze–formed specimen is around 50 pm, which is much smaller than that shown in the original as–cast feedstock, 150 pm. The solid fractions of the primary particles around the bottom and the centre of the specimen are much larger than those at the top and around the edge, respectively. The degree of the segregation of the primary particles in the non–dendritic specimen is significantly smaller than that in the dendritic specimen. The hardness is lower at the location where the primary solid phase is the major constituent, while the hardness is higher at the location where the eutectic phase is the major constituent. The overall hardness of the non–dendritic specimen is lower than that of the dendritic specimen.