Effect of TiB2 Particles on Microstructure of 7075 Al Alloy in Semi-Solid State Near Liquidus

TiB2/7075 Al matrix composites were formed by in situ reaction, and effect of the TiB2 particles content on microstructure of 7075 Al alloy in semi-solid state near liquidus were investigated. The results have shown that the average grain size decreased with increased the amount of TiB2, and the microstructure became uniform rosette grains. The morphology of grains became big dendrite grains when the particles content were over 4.5 mass%. Globular grains of 7075 Al alloy whose size reached 94 gm can be got for 7.5 min at 630 degrees C. The minimum grain size of 3 mass%TiB2/7075, 4.5 mass%TiB2/7075 and 9 mass%TiB2/7075 Al matrix composites at 630 degrees C were 88 mu m, 51 mu m and 69 mu m for 30 mm, 20 min and 50 min, respectively. The TiB2 particles located in the grain boundary can hinder the Al atoms from diffusing within the semi-solid state of the 7075 Al alloy and restrain alpha-Al phase growth, but it can be conducive to improve the stability of semi-solid slurry in near-liquidus thixoforming.