In-situ development of ZrB_2 particles and their effect on microstructure and mechanical properties of AA5052 metal-matrix composites

摘要

AA5052/ZrB_2 composites with different volume percent (i.e. 0, 3, 6, 9 and 10 vol.%) ZrB_2 particles were developed by in-situ reaction of molten M5052 alloy with two inorganic salts K_2ZrF_6 and KBF_4 at a temperature of 860 ℃. The in-situ composites were characterized by DTA, XRD, SEM, TEM for reaction analysis and morphology. Their mechanical properties like hardness and tensile properties were evaluated using standard methods. Morphology studies show that grain size of Al-rich phase reduces due to the presence of ZrB_2 particles. Microstructural studies also reveal the uniform distribution of second phase particles, clear interface, good bonding, dislocations and morphology of ZrB_2 particles. It is found that ZrB_2 particles are mostly in nano size with hexagonal or rectangular shape, however, few particles in micron size are also observed. Density and hardness of the composites increases with increase in the amount of reinforcement. Ultimate tensile strength and 0.2% yield strength (YS) also improved continuously with increase in the volume fraction of ZrB_2 particles up to 9 vol.% but beyond this composition strength reduced. It is important to note that with dispersion of ZrB_2 particles in base alloy an improvement in ductility is observed which is contrary to many other composites.