Enhancing strength and ductility of Al-matrix composite via a dual-heterostructure strategy

Aluminum matrix composites (AMCs) often have low ductility, which has been a long-lasting issue in the last few decades. This problem arises largely from the non-deformability of reinforcement particles, which leads to premature failure of the matrix-particle interfaces. Here we propose a new microstructural design strategy for AMCs: distribute the reinforcement particles non-uniformly to form dual-heterostructured AMCs. The zones with high-density particles are recognized as the hard zones, which carry less plastic strain than the particle-free zones to prevent premature interfacial failure. A dual-heterostructured Al-matrix nanocomposite is fabricated, in which AlN nanoparticles are distributed in a dual-level hierarchy: first level heterogeneous nanoparticle distribution and second level heterogeneous zones with different grain sizes. The dual heterostructure produced a unique dual level hetero-deformation induced (HDI) strengthening and hardening to produce high strength and ductility. The dual level HDI strengthening effect has been revealed by the inflection points on the loading-unloading-reloading stress-strain curves. Furthermore, the evolution of local strain fields during the in-situ tensile deformation directly proved the occurrence of strain partitioning, in which the ductile particle free zones have carried a larger strain than the hard particle rich zones. Dispersive shear strain bands are observed for the first time in AMCs. These findings are expected to help design other metal matrix composites with superior mechanical properties.