Abstract: Residual stress is a significant barrier to achieving dimensional stability and high-precision performance of metal matrix composites, especially in the aerospace field. This study systematically investigated the macroscopic and microscopic residual stress of 40 vol.% SiC/6xxxAl composites using neutron diffraction. Analysis confirms that macroscopic residual stress could be completely eliminated after annealing, whereas microscopic stress arising from the mismatch in thermal expansion coefficients between SiC and Al was preserved. Cryogenic treatment could induce transition of thermal elastic mismatch to local plastic deformation, promoting the formation of dislocation networks around SiC particles without significantly increasing the overall dislocation density and facilitating the effective release of microscopic residual stress. Based on these observations, a combined annealing and cryogenic treatment approach was established, enabling near-complete elimination of macroscopic as well as microscopic residual stress in SiC/Al composites.

Key words: Metal matrix composites, Neutron diffraction, Macroscopic and microscopic residual stress, Annealing, Cryogenic treatment