Microstructures and mechanical properties of an Al-Cu-Mg-Sc alloy reinforced with in-situ TiB2 particulates

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TiB2 reinforcing particulates (4 wt %) were produced in-situ via salt-melt reactions in an Al2618 wrought alloy containing 0.11 wt % Sc. The microstructure and mechanical properties of the TiB2/Al2618 composite are studied both as-rolled and T6 treated. Microstructural analyses revealed submicron-sized in-situ TiB2 particulates dispersed in both the intergranular and intragranular regions of the matrix. Energy dispersive X-Ray spectroscopy (EDS) discovered a high tendency of Sc enrichment in association with Al-Cu-Ni and Al-Cu-Mg intermetallics in the as-rolled composites. After T6 treatment, the Al-Cu-Mg type intermetallic is dissolved. Meanwhile, Al-Cu-Ni type intermetallic with the enrichment of Sc element remains. The TiB2/Al2618 composites have an evidently higher hardness than the Al2618 matrix alloy. The yield strength and ultimate tensile strength (UTS) are increased by 20% and 8% respectively with the introduction of TiB2 and a minor amount of Sc, while the ductility is affected adversely under both as-rolled and T6 treated conditions. Analysis on the strengthening mechanisms revealed an obvious beneficial effect of Sc on yield strength after T6 treatment, however, a limited role on the yield strength at the as-rolled state.