Processing of SiC nano-reinforced AlSi9Cu3 composites by stir mixing, ultrasonication and high pressure die casting

Abstract

Aluminium composites have been extensively developed for automotive applications due to their high specific strength. However, particle agglomeration, high porosity content, and weak reinforcement/matrix interface bond are prone to occur in the casting process. These arise during the introduction of the reinforcement, mould filling, and solidification process, especially when the particle sizes are approaching the nanoscale and are detrimental, with respect to the mechanical properties. By applying high pressure in conjunction with high cooling rates, an improved distribution of the reinforcing particles can be expected, as the high pressure improves the filling capacity of the composite melt, in which the fluidity is generally decreased by the added heterogeneous particles. The fine grain structure obtained under the high cooling rate is also beneficial for the distribution of the reinforcing nanoparticles during solidification. In this study, SiC nano-reinforced AlSi9Cu3 composites were developed by employing an Al–Cu-SiCnp master alloy, stir mixing, ultrasonication and HPDC technology. The findings showed a good distribution of individual SiC particles, resulting in a reduction of ∼40% in the α-Al grain size and near 10% increment in the yield strength, which was attributed to grain refinement, CTE strengthening and Orowan strengthening. Compared to commercial AlSi9Cu3 HPDC alloys, the developed AlSi9Cu3-1wt% SiCnp composite provided an improved YS of ∼187 MPa and a UTS of ∼350 MPa in the as-cast state and the milestone high YS and UTS of ∼370 MPa and ∼468 MPa under a T6 condition, respectively.