Tailoring properties of stir cast a356-tib2 in-situ composites

Abstract

In the present work, a stir casting process was used to produce TiB2 particle reinforced in-situ Aluminium-7% Silicon-0.3% Magnesium alloy (A356) composites. The various volume fractions of TiB₂ particles were produced inside the A356 melt via exothermic salt-metal reaction, i.e., the reaction of Hexaflurotitanate (K2TiF6) and potassium Tetrafluroborate (KBF4) halide salts with the molten master alloy. Stirring of the molten liquid with a preheated impeller was employed at the salts/aluminium interface to promote uniform mixing of the TiB2 particles. Three hybrid A356-TiB2 composites were prepared with an estimated amount of 5, 10 and 15 vol.% TiB2 in the matrix. Plates of dimension 20120220 mm were cast using greensand system with a pouring temperature of about 750 °C. Structural characterization of the composites was made using optical and scanning electron microscopy and x-ray diffractometry to determine the particle size distribution and morphologies of TiB2 particles and the microstructure of the silicon particles, eutectic, and primary aluminium grains. Mechanical characterization of the composites was determined using tensile testing and hardness measurements. Chemical characterization of the composites was made by dipping specimens in liquid media for a pre-determined time and then determining the corrosion rate. The master alloy (A356 alloy) and hybrid composites were also gonethrough age hardening treatment to observe its effect on properties. The effects of foundry variables (such as casting temperature, stirring speed and type of mould materials) and ageing conditions were assessed to tailor the properties of these A356-TiB2 in-situ composites. It was observed that the addition of TiB2 particles to A356 alloys significantly alter the particle size distribution of TiB2particles, which consequently affect the mechanical properties of the composites. Hardness and tensile values were generally increased but only with 10% TIB2 appeared to yield the best result. The corrosion rate was decreased with 10%TiB2 is added to A356 master alloy.The age hardening response of all four materials showed predictable behaviour.