Behavior of Precipitation Kinetics of 7050 Aluminum Alloy Die Forgings in Quenching Processes
WU Shu-zhou1,2, YI You-ping1,2, HUANG Shi-quan1,2
1. College of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China;
2. State Key Laboratory of High Performance Complex Manufacturing, Central South University, Changsha 410083, China
Abstract：The time-temperature-property (TTP) curves of 7050 aluminum alloy die forgings were determined by an interrupted quenching method. The second phase dissolving and precipitation mechanism and the strengthening mechanism were studied by TEM and JMA equation.The results show that the nose temperature and incubation period of TTP curves are 337℃ and 0.7s, with the quenching sensitivity range 270-400℃. Low level of the quenching sensitivity to sort the result followed by high temperature, low temperature, medium temperature; Al3Zr particles are the primary nuclear sites of supersaturated solid solution, whose main precipitate phases are η particles during early isothermal process, with the increase of temperature, the grain boundary becomes narrower; after the holding time is prolonged, needle dispersion S phases are the main precipitates of the alloy in the low temperature range; in the medium and high temperature range, a large number of η particles precipitate and aggregate, accompanied by the decrease of volume fraction of S phases, meanwhile the grain boundary becomes coarser and continuous; with the temperature rising, the size of η particles increases while the amount decreases; the rank of strength levels of precipitation is GP zones and η' phases, needle-like S phases, clubbed η phases.
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