Characterization of in-situ reinforced (Al,Si)3(Ti,Ce) precipitates in T6 treated A356-0.3wt.%Ce-1.5vol.%TiCN composite and its effects on mechanical properties

In the present study, the microstructural evolution and mechanical properties of T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite were studied. The results demonstrated that the grain refinement and eutectic Si modification effects of T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite are remarkable than that of T6 treated A356 alloy, and similar to that of T6 treated A356–0.3wt.%Ce alloy. More importantly, the in-situ reinforced (Al,Si) 3 (Ti,Ce) precipitates were found in T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite. TEM results and simulated diffraction pattern corresponding to the proposed crystal structure indicated that the (Al,Si) 3 (Ti,Ce) precipitates could be indexed consistently according to a body-centered tetragonal structure (I4/mmm space group, D022 type) with lattice parameters approximately of a = 0.519 nm and c = 0.859 nm. The existence of (Al,Si) 3 (Ti,Ce) precipitates resulted in the increase of strength due to the load bearing and coefficient of thermal expansion (CTE) mismatch strengthening. Besides, the fracture mode of the T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite is a transgranular fracture. Compared with the T6 treated A356–0.3wt.%Ce alloys, A356–0.3wt.%Ce-1.5vol.%TiCN alloys showed better elongation, which is ascribed to the transformation of needle-like and hard Ce-rich phases distributing along with the eutectic Si to blocky and relatively soft (Al,Si) 3 (Ti,Ce) phases. The ultimate tensile strength (UTS) and the elongation (El) of the A356–0.3wt.%Ce-1.5vol.%TiCN composite were increased by 3.7% and 32.7% than that of the A356–0.3wt.%Ce alloy, respectively. • The Ti-containing reinforced phases were identified as (Al,Si) 3 (Ti,Ce) phases. • The (Al,Si) 3 (Ti,Ce) crystal structure is proposed relying on the TEM and DFT characterization. • The (Al,Si) 3 (Ti,Ce) precipitates results in the increase of YS due to the load bearing and CTE mismatch strengthening. • The A356-0.3wt.%Ce alloy with TiCN shows better elongation due to the formation of (Al,Si) 3 (Ti,Ce) precipitates.