| Al-Zn-Mg-Cu series alloys have the characteristics of low specific gravity,high strength,high fracture toughness,good corrosion resistance,and excellent processing performance.They are widely used in aerospace,automobile,shipbuilding,and military industries.However,their low strength and poor creep resistance at high temperatures limit the application range of the alloy.Adding trace elements to Al-Zn-Mg-Cu alloys to improve the overall properties of the alloys has become a research hotspot in recent years.In this study,one Al-Zn-Mg-Cu-Zr-Sc alloy casting was prepared by squeeze casting technology.The high temperature mechanical properties,microstructure evolution,and deformation mechanism of the Al-Zn-Mg-Cu-Zr-Sc alloy under different deformation conditions were investigated by using high temperature tensile test,metallographic microscope(OM),scanning electron microscope(SEM),and transmission electron microscope(TEM).The experimental results show that:(1)Adding the rare earth element Sc to the Al-Zn-Mg-Cu-Zr alloy creates the primary Al3(Sc,Zr)particles during solidification,which function as the core of heterogeneous nucleation to significantly refine the grains and make the grain size of the alloy more uniform,and improve the deformation coordination of the alloy.(2)Both of the strength and the elongation of the Al-Zn-Mg-Cu-Zr-Sc alloy improve with the addition of the rare earth element Sc to the Al-Zn-Mg-Cu-Zr alloy.The alloy exhibits the highest tensile strength of 181.63 MPa at the strain rate of 10-2s-1 and the temperature of 300?,representing an increase of 21.6%;the alloy exhibits the highest elongation of 76.7%at the strain rate of 10-2s-1 and the temperature of 450?,representing an increase of 10%.(3)A large amount of?'phase,?phase,and fine Al3(Sc,Zr)particles precipitate at the low deformation tempeartures.These particles can pin the dislocations,increase the strength of the alloy;with the increase in temperature,the amount of precipitates gradually decreases and their size increases,and the?'phase gradually transforms into the?phase;however,the secondary precipitated Al3(Sc,Zr)particles do not change significantly,showing good thermal stability.In addition,no significant recrystallization occurs with the increase in deformation temperature,and the major softening mechanism is dynamic recovery.(4)The creep activation energy of the alloy significantly increases with the addition of the rare earth element Sc,indicating an enhanced creep resistance.In addition,the stress exponent of the alloy decreases with the increase in temperature,indicating a changing creep mechanism from the mechanism controlled by the strengthening of the second phase particles to dislocation climb creep.The stress exponent of the alloy is n?5 under the deformation temperatures of 400??450?;the creep activation energy of the alloy is Q=167.16 k J·mol-1when(?)=10-2s-1 and Q=148.09 k J·mol-1 when(?)=10-3s-1,and the latter is close to the self-diffusion activation energy of Al.Therefore,the main high temperature deformation mechanism of the Al-Zn-Mg-Cu-Zr-Sc alloy is dislocation climb creep. |
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