Study Of Thermal Fatigue On Al-Cu-Mn-Ti-Ce Alloy

The experiments are carried out under the conditions which similar to the practical surroundings, using the thermal fatigue tester to do the study on the rule of initiation and propagation of thermal fatigue crack. Optical microscope, SEM, energy spectrum analysis, tensile tests, hardness tests and thermal fatigue tests have been used on 4.5%A1-Cu alloy to study the effect of microelements on thermal fatigue performance of Al-Cu alloy and the mechanism of initiation and propagation of thermal fatigue crack.The thermal fatigue samples with prefab crack have been chosen. The period from the initiation of the crack to the length reaches 0.2mm has been defined as the initiation period of thermal fatigue cracks. The period that the cracks propagate to more than 0.2mm and later has been defined as the propagation period of thermal fatigue cracks. The cold and hot cycle times is used to measure the resistance to the initiation of thermal fatigue of different microelements when the lengths of the cracks reach to 0.2mm. The length of thermal fatigue cracks under same cycle times is used to measure the resistance to the propagation of the thermal fatigue cracks from different microstructure.The main conclusions that gained under the above conditions are as follows:The thermal fatigue performance of Al-Cu alloy has been improved when added in proper amount of Mn, Ti and Ce, and that with Ce has the best thermal fatigue performance and the most circular times while the cracks are initiated. The microelements can refine the structure, but with the different mechanisms, Mn and Ti are distributed in crystal grain, while Ce is enriched in grain boundary, as the added microelements increasing, the thermal fatigue performance and parts of mechanics performance are first enhanced, then declined. The propagation mode of the cracks is mixed propagation: the cracks are propagated in grain boundary and intercrystalline cracking, the cracks with the trend of trancrystalline cracking quickly stopped their propagation or trancrystalline cracking developed to a certain extent then turn to intercrystalline cracking, the alloy thermal fatigue mechanisms are related to the tips of prefab cracks and the inner oxidation of formative tiny cracks, oxidation greatly advanced the initiation and the propagation of the thermal fatigue cracks, the thermalfatigue performance cannot be measured just by single mechanics performance index, but the path to gain better thermal fatigue resistance is related to the intensity, plastic nature, tenacity and rigidity of the structure itself.The thermal fatigue performance of the alloy structure with Ce is superior to that with Mn and Ti under the same conditions. The Al-Cu alloy with 0.3%Ce is considered to be with the best thermal fatigue performance.