The role of TiB2 nanoparticles in reducing the microstructural sensitivity of as-cast Al-Mg-Mn alloy to cooling rate

In the production of large billets from Al-Mg-Mn alloys, non-uniform microstructures and properties usually occur at different locations due to thermal differences, which can have a detrimental effect on subsequent processing. This work presents a new idea to solve this challenge by introducing in-situ TiB2 nanoparticles (NPs) into the casting process. The effects of TiB2 content on the microstructure and mechanical properties of the Al-Mg-Mn alloy were investigated. It was found that TiB2 NPs can reduce the microstructural sensitivity of the alloy to the cooling rate in three ways: 1) as effective nucleation sites for α-Al, TiB2 can improve nucleation and restrict dendrite growth; 2) reduces grain size difference and disperses pore distribution; 3) hinders the diffusion of elements and significantly weakens their segregation. As expected, the addition of NPs improves the mechanical properties of the Al-Mg-Mn alloy. The billets produced by this method can be subjected to appropriate plastic processing without homogenization annealing thanks to the above-mentioned advantages. It is worth noting that the ductility of the samples solidified at slower cooling rates is more sensitive to the casting defects and that the addition of NPs can simultaneously improve the strength and elongation. The strength increase caused by TiB2 NPs is mainly attributed to grain refinement and thermal mismatch enhancement. This work explains the mechanism of microstructural evolution during solidification and can provide insight into the production of cast billets from a high-performance Al alloy.