The measurement of the residual stress in aluminum alloy die castings by x-ray method was investigated in order to apply this method for improving the analysis accuracy of the deformation of aluminum alloy die castings. The residual stress of one flat type experimental die castings and six kinds of practical die cast products were assessed by the x-ray method. As a result, the stress occurring in a deformed die castings was found to be measurable by the x-ray method. However, the residual stress in the as-cast die castings measured by the x-ray method showed a lower compressive value than that measured by the stress relaxation method in which the die castings was cut off and the residual stress was measured by strain gauges. The cause of the inconsistency between the x-ray method and stress relaxation method was estimated as the decrease in the lattice constants of aluminum measured by x-ray due to the solid solution of silicon and copper in aluminum. Therefore, the x-ray method can be used to measure the residual stress in die castings after being calibrated by the stress relaxation method. The residual stress on the surface of the die castings was found to become tensile stresses after heat treatment at 200℃ or 250℃.
