Microstructure and mechanical properties of AA6061–5wt. %TiB2 in-situ metal matrix composite subjected to equal channel angular pressing

Abstract

Abstract Aluminum alloy 6061–5wt. %TiB2 in-situ metal matrix composite was produced by a salt-melt reaction between halide salts K2TiF6 and KBF4 inside AA6061 melt. The composites prepared were subjected to equal channel angular pressing (ECAP) up to 10 passes at ∼300\u202f°C (0.45 Tm of AA6061). The improvement in strength and Vickers hardness due to grain refinement and redistribution of in-situ TiB2 particles was studied. The AA6061 (without TiB2) was also subjected to ECAP to identify the improvement arising from the presence of TiB2 particles and their redistribution in the AA6061-TiB2 composite. The microstructures of the AA6061 alloy and the composite were studied using Electron Back Scattered Diffraction (EBSD). The Vickers hardness and tensile strength of the alloy and the composite were evaluated as a function of the variables of the ECAP process. After 10 ECAP passes, the average grain size of AA6061 alloy had decreased from ∼87\u202f±\u202f11\u202fμm to ∼20\u202f±\u202f2\u202fμm. In contrast, the average grain size of the AA6061-TiB2 composite after 10 passes had decreased to ∼5\u202f±\u202f2\u202fμm from ∼37\u202f±\u202f9\u202fμm. There was an increase in the Vickers hardness of AA6061 alloy from ∼54\u202f±\u202f1 HV to ∼64\u202f±\u202f1 HV and the AA6061-TiB2 composite showed a hardness improvement from ∼57\u202f±\u202f1 HV to ∼69\u202f±\u202f1 HV. Compared with the as-received parent material, the yield strength of the alloy subjected to 10 ECAP passes had increased from ∼105 to ∼149\u202fMPa while the ultimate tensile strength increased from ∼123\u202fMPa to ∼153\u202fMPa after 10 ECAP passes. The yield strength of the AA6061-TiB2 composite increased from ∼113\u202fMPa (annealed) to ∼167\u202fMPa after 10 ECAP passes while the ultimate tensile strength increased from ∼146\u202fMPa to ∼177\u202fMPa for the same treatment. EBSD results show that after 10 ECAP passes there is an increase in the percentage of high-angle grain boundaries (HAGBs) from 46% to 51% in the AA6061 alloy and an increase from 18% to 60% in the AA6061-TiB2 composite.