Study on microstructure evolution of Al-Zn-Mg-Cu alloy during processing
The microstructure evolution of alloy 7175 during machining was studied by Jmatpro thermodynamic calculation,optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that the ther-modynamic equilibrium phase of 7175 aluminum alloy is composed of AlCrMgMn phase,Mg2Si phase,Al6Mn phase,Al2CuMg phase,MgZn2 phase and AlCuMgZn phase,and there is a small amount of impurity phase(Al7Cu2Fe phase)in the actual state.After extrusion and solid solution,the microstructure of 7175 aluminum alloy profiles is mainly fibrous grain structure,without obvious recrystalliza-tion.After holding temperature at 475℃for 2.5 h,the second phase of small size is basically redissolved,and the undissolved phase of large size is Al7Cu2Fe phase and Mg2Si phase,which is distributed along the grain boundary in chain fracture.The dispersive phase AlCrMgMn is always present during solution and aging,and the precipitated phases in the aged state are spheroid η′ phase and a small amount of tabular η phase.The precipitated phase MgZn2 is discontinuously distributed at the grain boundary,and the width of precip-itation-free zones at the grain boundary ranges from 35 nm to 45nm.
7175 aluminum alloyfibrous grain structuresecond phaseprecipitated phaseprecipitation-free zones
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