Research On Compressive Creep Behavior Of The High Aluminum Zinc Based Alloy

Among zinc-aluminum cast alloys, ZA27 alloy exhibits attractive physical and mechanical properties combined with good friction and wear resistance, making it a bearing alloy replacing of some copper alloys, also this alloy tend to be used widely. In this dissertation, the development and research on the ZA27 alloy are systematically presented, and then the compressive creep behavior of the ZA27 alloy is investigated at different temperature and compressive stress with special apparatus. And also the phase transformation, microstructural evolution and the effects of RE, Mn and Zr elements are researched.The effects of casting methods, stabilized heat treatment and modifiers(RE, Mn and Zr) on the compressive behavior of the ZA27 alloy are investigated extensively. It shows that there was good linear logarithmic relationship between the steady creep rate and all of temperature and stress used. The Steady creep rate obeyed an empirical equation εs=A σnexp( - Qc/RT) or εs=At on exp( - Qa/RT) . The compressive creep rate in the alloy was mainly controlled by the lattice diffusion of zinc and dislocation limb, and the grain boundary sliding contributed for it in some degree.The reason why the negative creep occurred during compressive creep was deeply analyzed with the phase transformation and using XRD,TEM and SEM techniques. It was found that the negative creep resulted from volume expansion caused by the four-phase transformation, alpha+ε→T' +ηn, in the alloy, and the values of negative creep depended on the difference between the compressive creep deformation and the volume expansion. The microstructure changed partly from lamellar structure into spheroidized structure with thecompressive creep strain during compressive creep.The compressive creep resistance of ZA27 alloy increased after added some RE, Mn or Zr elements, but it is converse for addition of Zr at 160℃. These are analyzed extensively with the microstructural change. It is found that the grain size and the complex constitute compound located in grain boundary have a great influence upon the creep, coarsening the grain and the complex constitute compound is useful to increase the creep resistance.