Structure-Property Correlation of a Newly Synthesized 6351Al/Body-Centered Tetragonal Boron Nitride Composite

In this work, a novel body-centered tetragonal boron nitride (bct-BN)-reinforced 6351Al-based cast metal matrix composite of various reinforcement contents is synthesized for the first time adopting a low-cost hybrid route of liquid metal infiltration-cum-stir casting followed by subsequent treatments of forging and age hardening. Not only a new low-density ultra-hard reinforcement (bct-BN) is incorporated but also a new hybrid casting route pertinent to the low-density reinforcement incorporation is attempted for the first time in order to achieve high specific ultimate tensile strength (SUTS) value. As a noteworthy outcome, a significant value of SUTS (113 MPa/g cm −3 ) and modest ductility (%Elongation = 10) are achieved in 6351Al-12.3 vol.% BN composite on casting followed by forging and age hardening treatments that is quite comparable or superior to many common aluminum-based metal matrix composites and steels for structural application. In view of structure-property correlation, such an enhanced property (YS = 196 MPa, UTS = 291 MPa, % Elongation = 10, SUTS = 113 MPa/g cm −3 ) as compared to the initial property of cast 6351Al alloy (YS = 131 MPa, UTS = 144 MPa, % Elongation = 2, SUTS = 56 MPa/gcm −3 ) is attributed to reinforcement effect of coherent bct-BN particles, matrix grain refinement effect on bct-BN particle incorporation, evolution of nano-twinned region within BN particle on forging and the age hardening effect of coherent Mg 5 Si 6 ( β ″) precipitates. This asserts an emergence of a new cost-effective structural material in the form of 6351Al/bct-BN composite.