<p>The formation of potential entrainment defects (oxides, irregularly shaped pore, and regular pore) during the semi-solid slurry preparation stage can result in the reduced performance and inconsistent mechanical properties in rheocast components. The influence of entrainment defects in semi-solid slurries during extrusion deformation on mechanical properties, as well as the mechanism of defect elimination, has not yet been fully investigated and understood. This study investigates both aspects. The results show that extrusion deformation processing effectively refines primary α-Al grains in C611 aluminum alloy semi-solid slurry, enhancing their shape factor while simultaneously reducing the total count, volume fraction, porosity, and pore number density. During extrusion deformation, the shear stress disrupts the oxide films of oxide bifilm and irregularly shaped pore. The flow stress drives molten metal infiltration from fractured zones into the air gaps of oxide bifilm and irregularly shaped pore, forming stress-bearing penetrated substrates and bridging connections. The penetrated melt reacts with air trapped in the defects, while flow stress and flow strain induce contraction and closure of irregularly shaped pore and regular pore, which combined effects lead to a reduction in the sizes of oxide bifilm, irregularly shaped pore, and regular pore. An increase in the extrusion ratio from 1:1 to 8:1 results in an enhancement of tensile strength from 125 to 165&#xa0;MPa and an increase in elongation from 3.7 to 6.5%. The elimination of entrainment defects induced by extrusion deformation can significantly improve the tensile performance of the samples.</p>