Study Of Thermal Fatigue And Mechanical Properties Of Multiple Zinc And Aluminum Alloys

With the development of the society,there is an increasing demand for the use of materials.Materials are needed to possess of better performance when in practical environment.In practical use,fracture is one of the most important forms for materials to be invalided,which will cause great loss for people.A lot of fracture accidents take place because of material fatigue.Because of the sharp working circumstance and undergoing higher temperature,multiple zinc-aluminum alloy is more likely to be invalided,so considering thermal fatigue property is an important measuring method.The thermal fatigue samples with prefab crack have been chosen. The period from the initiation of the crack to the length reaches 0.1um has been defined as the initiation period of thermal fatigue cracks.The period that the cracks propagate to more than 0.1um and later has been defined as the propagation period of thermal fatigue cracks.The cold and hot cycle times when the length of the cracks reach to 0.1um is used to measure the resistance to the initiation of thermal fatigue of different components alloys;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 samples.Then we use the different heat treatment methods of solution and aging.It can probe into the resistance of thermal fatigue of different samples after heat treatment. Also the mechanical properties are studied in this work. The main conclusions that gained under the above conditions are as follows:Cracks are initiated in the defect of the samples which is near the gap,then extend to the stress centralized area.The thermal fatigue property of casting sample of 2.7wt%Si-0.08wt%RE is prior to 2wt%Si, 3.5wt%Si-0.14wt%RE,3.5wt%Si-0.2wt%RE samples.The resistance of thermal fatigue about different samples is improving after solution and aging.Reasons are as follow:first,we can obtain more alloying structures after heat treatment;second,it is more likely to be spheroidized which can improve the plastic strain of sample.Third,the weeny carbide has the function of postponed the propagation of fatigue cracks.It is concluded cooling in air is the best way.After comparing mechanical properties of tested samples,it shows 2.7wt%Si-0.08wt%RE sample is prior to 3.5wt%Si-0.14wt%RE and 3.5wt%Si-0.2wt%RE samples.The thermal fatigue performance and mechanical properties of alloy has been improved when added in proper amount of RE.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 trancrystaUine cracking developed to a certain extent then turn to intercrystalline cracking.