Microstructure and Viscosity of Particles Reinforced 7075 Al Matrix Composites

Abstract

In-situ TiB 2 particle reinforced 7075 Al alloy was produced by molten salt method (LSM). The effects of TiB 2 content on the microstructure, the melting behavior and the viscosity of 7075 Al alloy were investigated. The experimental results have shown that the microstructure became uniform rosette grains and the grain size decreased with increasing TiB 2 particles. The morphology of grains became bigger with dendritic structure when the TiB 2 particles content is more than 4.5% . The liquidus and solidus temperatures of the TiB 2 /7075 composites were rstly increased and then decreased with the increase of the content of TiB 2 particles. The semisolid processing temperature window of 7075 Al alloy became narrow after adding TiB 2 particles, and the liquid fraction of TiB 2 /7075 composites with increasing temperature was more sensitive than 7075 Al alloy. The apparent viscosity of the 4.5%TiB 2 /7075 composite was the lowest among 3.0, 4.5 and 9.0%TiB 2 /7075 aluminum matrix composites respectively. The apparent viscosity of the 9.0%TiB 2 /7075 was less than that of 7075 alloy but was greater than that of 4.5%TiB 2 /7075 composite under the same conditions. The viscosities of the composites decreased sharply with increasing shear rate, and the change with the shear rate were more sensitive than that of the 7075 alloy.

Microstructure Evolution of TiB₂/7075 Composites in Semi-Solid State near Liquids within Holding Time

“…The liquidus and solidus temperatures of 7075 Al alloy are 635°C and 474°C respectively. The liquidus temperatures of 3.0%, 4.5% and 6.0%TiB 2 /7075 Al matrix composites are 643.1°C, 639.6°C and 644.8°C with heating speed of 5°C/min respectively, the solidus temperatures of 3.0%, 4.5% and 6.0%TiB 2 /7075 Al matrix composites are 605.3°C, 600.7°C and 597.5°C respectively [11] . The liquidus and solidus temperatures of TiB 2 /7075 Al matrix composites firstly increase then decrease with the increase of TiB 2 content.…”

“…7075 Al alloys have been widely used as structural materials in aeronautical industries due to their attractive comprehensive properties, such as low density, high strength, ductility and toughness, but 7075 Al alloys had a relatively coarse dendrites which made manufacturing with semi-solid slurries difficult. Previous work has shown that SSM processing were appropriate for 7075 Al alloy by adding TiB 2 particles, including rheocasting and thixocasting [7][8][9][10][11][12] . However, the particles were easy to settle resulting in non-uniform microstructures which affected its performance.…”