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The thermal expansion behaviors of SiC whisker reinforced commercially pure aluminum composites subjected to different heat treatments were studied. The results indicated that the thermal expansion behaviors were greatly affected by heat treatment.To explain the results, the microstructures and thermal mismatch stresses in the matrix of the composite were examined by the transmission electron microscope and Xray diffraction, respectively. The dislocation density and thermal mismatch stresses in the matrix of the composites water quenched from 600°C are much higher than that of the composite slowly cooled from 600°C. The analysis suggested that the coefficients of thermal expansion (CTE) are closely related to the change of thermal mismatch stresses and yield strength of the matrix of the composite. The comparison of the coefficients of thermal expansion between experiments and calculations suggested that the temperature behaviors of CTE of SiCw/Al composite agree better with those of Ker’s model within lower temperature range.