Rheological behavior of semi-solid TiB2/7075 composites and simulation of their rheocasting processes

In the present study, in-situ TiB2 particle-reinforced 7075 aluminum alloy was produced by adding a mixture of K2TiF6 and KBF4 to the molten base alloy. The effects of the addition of 4.5wt.% and 9wt.% TiB2 on the apparent viscosity and microstructure were investigated. The results showed that adding TiB2 is effective for optimizing primary alpha-Al, but compared with the 4.5wt.% TiB2/7075 composite, the addition of 9wt.% TiB2 had no further significant refinement role in the 9wt.% TiB2/7075 composite due to particle aggregation. The viscosities of semi-solid 7075 alloy and TiB2/7075 composite slurries increased with an increase in solid fraction, but decreased with an increase in shear rate. The viscosity of 4.5wt.% TiB2/7075 was the lowest among the three samples, and that of 7075 alloy was the highest under the same conditions. The primary a-Al grain size was decreased, and the dendritic grains grew into spherical shapes after shearing. Based on the experimental results, viscosity models of the semi-solid 7075 alloy and 4.5wt.% and 9wt.% TiB2/7075 composites were formulated. According to the simulation results, the shrinkage porosity of the 4.5wt.% TiB2/7075 wheel was lower than those of the 7075 alloy and 9wt.% TiB2/7075 wheels.