The Influence Of Modification And High Temperature Fatigue Performance Of Zl114a Alloy

In order to develop a new engine material for diesel engine head, modification, heat treatment and alloying treatment for ZL114A were investigated in systematic way. The effects of Sr modification on the microstructure and mechanical properties of ZL114A alloy were studied by the addition Al-Sr master alloy. The effects solution treatment was investigated by using different heat treatment technic. The high temperature tensile strength and fatigue property of the ZL114A after alloying treatment were studied by using fatigue testing machine. The optimum composition for high temperature property was determined by combining the results of high temperature tensile and fatigue test. A theoretic relation between fatigue life and fatigue strength was calculated, which is well consistent with the test results. The conclusion of the present study is as follows:The spheroidization of eutectic phase during solution treatment was accelerated by Sr modification. However, an elongated solution treatment will resulted in a congregation and growth of the eutectic phase. At the optimum condition (8 hours solution treatment at 535℃for 8 hours, ageing at 165℃for 16hours,0.03%Sr addition), the tensile strength, elongation and hardness are 305MPa,8% and100HB, respectively.An optimum chemical composition for high temperature strength and fatigue property was obtained for ZL114A alloy. Minor addition of 0.07%Fe,1.53%Cu and 0.16%Ni can improve the high temperature propertys because of high Cu/Mg atomic ratio and Ni content. The fatigue strength of ZL114A is 40.2MPa at 200℃, and after alloying treatment, the fatigue strength increases to 236MPa. The high temperature tensile strength is 194MPaå'Œ236MPa, respectively before and after alloying treatment. A theoretical model for fatigue life at 200℃was developed for the ZL114 alloy.Fracture surface was observed by SEM and it was found that the fatigue crack is always initiated from the cast defect which is located at the edge of specimen, The fracture of specimen is resulted from the subsequent crack propagation form the edge to the inner area of the specimen.