Solidification behavior and elimination of undissolved Al_(2)CuMg phase during homogenization in Ce-modified Al–Zn–Mg–Cu alloy

The solidification behavior and intermetallic phase evolution during homogenization annealing of an Al-Zn-Mg-Cu alloy with 0.12 wt%Ce addition were examined.The residual Al_(2)CuMg phase is completely dissolved after homogenization and is replaced by a large number of dispersed micro/nanoscaled AlCuCe enrichment phases within Al matrix.This change occurs because of the formation of a large number of finer lamellar eutectic network structures which are more easily dissolved into Al matrix during the homogenization process.In addition,the trapping of Cu atoms in the stable AlCuCe phase also prevents the formation of Al_(2)CuMg phase,leading to the complete dissolution of Al_(2)CuMg phase in the Al-Zn-MgCu alloy.The grain refinement behavior in Al alloy with Ce addition is similar to that in alloys with the addition of Sc,because of the formation of primary Ce-enriched Al_(11)Ce_(3)phase as the nucleation agent ofα(Al)during solidification.

Characterization of Hot Deformation Behavior of a Novel Al–Cu–Li Alloy Using Processing Maps

The isothermally compression deformation behavior of an elevated Cu/Li weight ratio Al–Cu–Li alloy was investigated under various deformation conditions.The isothermal compression tests were carried out in a temperature range from 300 to 500℃ and at a strain rate range from 0.001 to 10 s^-1.The results show that the peak stress level decreases with temperature increasing and strain rate decreasing,which is represented by the Zener–Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of 218.5 k J/mol.At low Z value,the dynamic recrystallized grain is well formed with clean high-angle boundaries.At high Z value,a high dislocation density with poorly developed cellularity and considerable fine dynamic precipitates are observed.Based on the experimental data and dynamic material model,the processing maps at strain of 0.3,0.5 and 0.7 were developed to demonstrate the hot workability of the alloy.The results show that the main softening mechanism at high Z value is precipitate coarsening and dynamic recovery;the dynamic recrystallization of the alloy can be easily observed as ln Z ≤ 29.44,with peak efficiency of power dissipation of around 70%.At strains of 0.3,0.5 and 0.7,the flow instability domains are found at higher strain rates,which mainly locate at the upper part of processing maps.In addition,when the strain rate is 0.001 or 0.02 s^-1,there is a particular instability domain at 300–350℃.