Abstract In this paper, the effects of heat treatment processes on microstructure, residual stress and dimensional stability of 70 vol.% SiC p /Al composites were investigated by using a field emission gun scanning electron microscope (SEM), the X-ray stress analyzer and the thermal cycling test method. The results showed that the matrix of the as-cast composite is in compression. After the solution-quenching (SQ), aging and thermal-cold cycling (TCC) treatment, the residual stress was reduced due to the plastic deformation of the matrix. With the increase in the numbers of the SQ treatment, the long rod Al(MnFe) 3 Si 2 phase and the blocky CuAl 2 phase decreased while the spheroidization of these intermetallics increased. The TCC treatment refined the size of these intermetallics. As the number of the TCC treatments is increased, the resistance to micro-plastic deformation of the composite was also enhanced. The composite, which experienced the three-step SQ and aging and 12 times TCC treatment, presented the optimum thermal stability. Its hysteresis strain achieved 0.26 × 10 − 5 , and remained constant during the second and third cycling tests. The excellent dimensional stability shows a promising potential to be used as mirror materials for preparing mirror substrates in industry.