Microstructure-property analysis of ZrB2/6061Al hierarchical nanocomposites fabricated by direct melt reaction

In our research, we successfully fabricated ZrB2/6061Al hierarchical nanocomposites by direct melt reaction between halide salts (KBF4 and K2ZrF6) and Al. The unique microstructure comprised two levels: 6061Al matrix reinforced by the clusters (level II composite) and the cluster itself consisting of ZrB2 nanodispersoids in an Al matrix (level I composite). Experimental observations demonstrated that the formation of level I composite depended on the reactive route, while the grain refinement in level II composite through varying ZrB2 content was owing to grain growth restriction. Compared with the unreinforced matrix, the prepared nanocomposites were significantly and simultaneously hardened, strengthened and made more ductile. The well-balanced strength and elongation achieved in 2 vol.% ZrB2/6061Al composite were substantially improved to approximately 1.52 and 2.75 times those of the 6061Al alloy. Quantitative analysis of the strengthening mechanism indicated that quench strengthening contributed the most to the yield strength of the composites. The impressive ductility increase was attributed to the presence of plastic slip bands and equiaxed dimples induced by the toughened clusters.