In this study, AlCoCrFeNi-based high-entropy alloy (HEA) powders were added into AlSi7Mg0.3 (A356) alloys to develop the mechanical propertiesMechanical properties of an A356 alloyA356 alloy. The production of HEA-reinforced Al-alloys was produced via a stir-castingCasting process. HEA powders were obtained by a self-propagating high-temperature synthesis (SHS) method followed by grinding. The effects of the HEA additions on the Al-alloys ratio (0.5, 1.0, 1.5, and 2.0 wt. %) on the microstructureMicrostructure and mechanical propertiesMechanical properties of the final products were investigated. The castingCasting temperature was selected as 750 °C, and the stirring duration was applied for 2 min. T6 heat treatmentT6 heat treatment was also applied to the produced metalMetals matrix compositesComposite. The tensile strengthTensile strength and hardness tests were conducted. MicrostructureMicrostructure characterizationCharacterization was realized by using an optical microscope. The results show that the compositeComposite products meet the limit values of the mechanical propertiesMechanical properties requested by the car manufacturers after the heat treatmentHeat treatment process. While the highest average yield and ultimate tensile strengthsTensile strength were obtained as 175.6 and 225.7 MPa, respectively, in the A356-1.5 wt.% HEA compositeComposite, the highest average hardness value was obtained as 85.5 HB in the A356-2.0 wt.% HEA compositeComposite and the highest average elongation value was obtained as 3.45% in the A356-0.5 wt.% HEA compositeComposite.