Automobile engine materials require higher thermal fatigue resistance with increasing combustion temperature. In this study, a new test method for evaluating the thermal fatigue resistance of aluminum alloys has been developed. In this method, a small test piece was clamped between a pair of holders consisting of a low-thermal expansion material. The test piece was alternately heated and cooled with the longitudinal thermal expansion constrained. Temperature distribution of the test piece was within 5K. The total strain range was kept almost constant during the test. Thermal stress-strain behavior was quantitatively estimated using high-temperature strain gages. By applying this test method to JIS-AC2B-T6 aluminum alloy castings, the fracture behavior and the effect of porosity on the thermal fatigue lives were studied. The obtained results are as follows : The maximum tensile stress at the lowest temperature decreased rapidly with fast crack propagation and then the fracture occurred; it has been quantitatively clarified by using this test method that decreasing total strain range and reducing porosity increased thermal fatigue lives of the alloy castings; the fracture mechanism was changed by the total strain range, affecting the correlation between the porosity and the thermal fatigue lives.
�@