Abstract
The compositional dependence of thermal expansion coefficient of in-situ Al-Si composites has been measured. The thermal expansion coefficient of the Al-Si composites linearly decreases as the volume percent of precipitated Si decreases, almost equal to the rule of mixture. Based on this measurement, a numerical calculation has been carried out on the thermal stress distribution in a centrifugally cast Al-Si thick wall tube, in which the content of the Si precipitates gradually changes in the radial direction. The calculation was made under the condition that temperature decreases linearly along the tube thickness from the inner to the outer wall, while the thermal expansion coefficient and the elastic constant vary linearly towards the outer wall because of the decrease of the Si precipitates. The results are as follows: 1) In the range from the inner to the middle part of the wall thickness, the tangential and axial stresses are more relaxed than that with an assumption of the thermal expansion coefficient to be constant, whereas in the middle to the outer range, the thermal stress relaxation is indiscernible. 2) The biggest relaxation of the radial thermal stress would be at the middle part. 3) If the above through-thickness distributions of temperature and/or Si concentration are inverted, the thermal stress relaxation prevails throughout the wall thickness.
