Research On The Effect Of Casting Process On Segregation Defects Of ZL205A Alloy Large Axisymmetric-body Casting

In recent years,segregation in the axisymmetric-body casting?ZL205A?using for aerospace industry has been found frequently.It is harmful to the properties of the casting and casue hidden trouble to safety.In this paper,by using SEM,EDS,DSC,the effect of foundry technology and grain refinement on the fomation of segregation in ZL205A alloys has been researched.The resluts show that the segregation has a significant effect on the mechanical properties,microstructure,and appearance of fracture of the casting,appearing as:?1?fish pattern;?2?located in the joint between the slit gate and the casting;?3?the coarsen Al₂Cu distributed around the garin boundary.By using low pressure casting process,the improved deformability of the sand cores and the uniform temperature field of the casting are obtained,which are benefit for the decreasing of the temperature gradient and the resistance of solidification.Therefore,the segreaiton in the ZL205A alloys is improved significantly.The effect of multiple step of the additon of Al-Ti-B master alloy on the casting have been researched.The resluts show that the microsture of ZL205A have been refined significantly after the addtion of Al-Ti-B alloy.The mechanical properties,casting properties,flowability and thermal cracking performancd have been improved effectivly.The grain brige began to form in the ending process of the solidfication,which enhancing the bonding force among the grain boudary.The grian refiniment can significantly increase the contact area among the grain boundaries and grain boudaries.Therefore,the bonding force of the grain boundaries improved obviously with the relative slow intergranular separation process.Consequently,the grian refinement and optimization of the low pressure casting process can improve the segregation defect effectivly.