Force–Thermal Coupling Effects on Surface Integrity and Subsurface Damage of Al-50 wt% Si Alloy During Milling

Al-50 wt% Si alloy is widely used in aerospace and electronics but is hard to machine owing to uneven microstructure. To elucidate the relationship between force–thermal coupling effects and surface integrity during Al-50 wt% Si alloy milling, this paper established a stress model to reveal the superposition mechanism of mechanical and thermal stresses. Experiments were conducted to investigate the evolution of cutting forces and temperatures, as well as their influence on surface integrity characteristics, including microhardness, roughness, and chip morphology. The results showed that temperature increases steadily with vc, whereas cutting force fluctuates in an irregular manner. The maximum cutting temperature rises by 85.04% as vc increases from 25 m/min to 125 m/min. Meanwhile, the thermo-mechanical coupling effect exerts a regulatory role on chip morphology, where higher vc improves chip continuity and ductility. Surface integrity is determined by the competitive interplay between work hardening and thermal softening, and the surface microhardness varies from 168.49 HV to 173.27 HV. Specifically, elevated vc optimizes surface quality, with the Ra decreasing by 24.54%, whereas excessive fz and ap aggravate damage. Ultimately, surface defects arise from the combined removal behavior of Si particles and deformation of the Al matrix, while the inhomogeneous stress field induces subsurface damage.