Abstract: Piston is one of the key parts of high-density diesel engine for military vehicles. Thermal-mechanical coupling stress is produced under the combined action of mechanical load and thermal load, and the piston is prone to fatigue failure. In order to solve the above problems, this paper systematically studied the evolution of microstructure and mechanical properties of Al-based materials under thermal/mechanical coupling by means of OM, SEM, EDS and TEM. The results show that cyclic softening occurs at 350 C, and the size of silicon phase changes with heating temperature and holding time. The reason is that as the temperature increases and holding time prolongs, the silicon atoms are activated to diffuse to the surface of the original silicon phase, and the size of the silicon atoms is obviously increased, and the toughness of the material is reduced. At 350 C, the toughness of the material increases and the crack propagation speed decreases. The crack propagation will bypass SiC and propagate along the matrix. The deflection of the crack causes the crack closure effect and the high temperature fatigue performance of the material is improved significantly.