"The effect of temperature and third element addition on the properties of Al-base alloy"

Abstract

The transient creep tests of Al-1.0wt%Ag, Al-1.0wt%Ag-0.5wt%Cu and Al-1.0wt%Ag-0.5wt%In are studied under different constant stresses from 78 MPa to 91MPa for the first alloy and third alloy and from 91MPa to 104Mpa for the second one, near the transformation temperature. The results of the first and third alloy showed a transition point at 483K, while the transition point for the second alloy was at 493K. Hence, they represented low and high deformation temperature region below and above the transition temperature for each alloy. The transient creep was described by the equation: εtr=βtn where εtr and t are the transient creep strain and time. the parameter β and n are calculated. The parameter β was related to the steady state creep ε.st the equation β=βo(ε.st ) ɣ . The activation energies of the transient creep were ranged from 10kJ/mole to 16kJ/mole in the low and high temperature regions for the three test alloys. These values characterize the dislocations intersection mechanism for the transient creep of the test alloys, in the low and high temperature regions. The steady state creep tests of Al-1.0wt%Ag, Al-1.0wt%Ag-0.5wt%Cu and Al-1.0wt%Ag-0.5wt%In are performed under constant stress conditions at temperatures ranging from 443 to 513K . The results of the first and third alloys showed a transition point at 483K, while the transition point for the second alloy was at 493K. These transition points represented two deformation temperature regions for each alloy. The low and high deformation region below and above the transition point. The variations of the strain rate sensitivity parameter m with the temperature ranged from 0.2 to 0.5, from 0.14 to 0.2 and from 0.25 to 0.90 for the three test compositions, respectively. Meanwhile, the activation energy of the steady were found 12.4kJ/mole, 13.9kJ/mole, were found 17kJ/mole, 20kJ/mole, and were found 14kJ/mole, 16.8kJ/mole, in the low and high temperature regions, respectively. X-ray analysis of the samples of the test alloys confirmed the above mentioned results and mechanisms.

The stress-strain curves of the slowly cooled and quenched Al-1.0wt.%Ag, Al-1.0wt%Ag-0.5wt.%Cu and Al-1.0wt.%Ag-0.5wt%In alloys were studied in the temperature range from 443K to 513K. The parabolic work hardening coefficient, the yield stress, the fracture stress and fracture time of the annealed and quenched samples decreased with increasing the deformation temperature. They exhibited a discontinuity at 483K for the first and the third alloys and at 493 for the second alloys. Hence, they presented two deformation temperature regions for each alloy, the low and high temperature region below and above the transition temperature. The microstructure of the test samples after deformation of Al-1.0wt%Ag alloy were investigated by X-ray technique. The X-ray integral intensity I, the full width at half maximum [FWHM] Δ2θ and the lattice parameter a decreased with increasing the temperature in the low and high temperature regions. However, they exhibited anomalous rise at the transition temperature 483K.