Al2519-T87 is a material mainly used in defense products. It is applied in armored vehicles as a bulletproof material in Korea. Al2519-T87 was generally developed as a plate material, and Johnson–Cook flow stress determination was conducted to carry out studies on welding and bulletproofing for joining. However, Johnson–Cook constitutive equation has difficulty expressing speed. An alternative is needed to address this issue. In particular, the cutting force used in manufacturing the product has a great influence on the cutting force due to speed and temperature. Therefore, in this paper, we aim to determine the flow stress of the S-K constitutive equation which can be applied in cutting simulation.