Warm-temperature tensile ductility in Al−Mg alloys

Abstract

Several binary and ternary Al alloys containing from 2.8 to 5.5 wt pct Mg were tested in tension at elevated temperatures (200 ЊC to 500 ЊC) over a range of strain rates (10 Ϫ4 to 2.0 s Ϫ1 ). Tensile ductilities of up to 325 pct were obtained in binary Al-Mg alloys with coarse grains deformed in the solute-drag creep regime. Under test conditions in which solute-drag creep controls deformation, Mg in concentrations from 2.8 to 5.5 wt pct neither affects tensile ductility nor influences strain-rate sensitivity or flow stress significantly. Strength is shown to increase with increasing Mg concentration, however, in the power-law-breakdown regime. The solute-drag creep process, which leads to superplastic-like elongations, is shown to have no observable grain-size dependence in a binary Al-Mg material. Ternary alloying additions of Mn and Zr are shown to decrease the strain-rate sensitivity during solute-drag creep, negatively influencing ductility. An important cause of reduced ductility in the ternary alloys during creep deformation is found to be a transition from neckingcontrolled failure in the binary alloys to cavitation-controlled failure in the ternary alloys investigated. An increase in ternary element concentration, which can increase the relative volume percentage of proeutectic products, increases cavitation.

Texture analysis of the transition from slip to grain boundary sliding in a discontinuously recrystallized superplastic aluminum alloy

“…Binary Al-Mg alloys containing from 2.2 up to 10 wt% Mg have been shown to exhibit stress exponents of nϷ3 and apparent activation energies of about 136 kJ/mol in this temperature and strain rate regime, values which are indicative of solute-drag control of creep [33]. However, recent work [34,35] has demonstrated that ter- nary additions of 0.25 wt% Mn, or more, in Al-MgMn alloys result in an increase in the stress exponent to a value of between 4 and 5 while activation energy values remain at about 140 kJ/mol. The increase in the stress exponent, n, to a value similar to that for pure metal behavior has been attributed to an effective reduction of Mg content due to interaction between the Mg and Mn solutes [34].…”

“…However, recent work [34,35] has demonstrated that ter- nary additions of 0.25 wt% Mn, or more, in Al-MgMn alloys result in an increase in the stress exponent to a value of between 4 and 5 while activation energy values remain at about 140 kJ/mol. The increase in the stress exponent, n, to a value similar to that for pure metal behavior has been attributed to an effective reduction of Mg content due to interaction between the Mg and Mn solutes [34]. Elongations to failure data obtained here are shown in Fig.…”

Advances in Transmission Electron Microscopy: Self Healing or is Prevention Better than Cure?

“…For coarse grained Al-Mg alloys deformed in the viscous glide regime, values for the maximum strain in excess of 300% can be obtained [56,57,58]. Such elongations are close to those found in conventional superplasticity of fine-grained Al-Mg alloys and are sufficient for many practical applications.…”

Deformation and Fracture at High Temperatures in an Al-Mg-Mn Alloy Sheet Consisting of Coarse- and Fine-Grained Layers

“…Therefore if the dominant deformation mechanism is the Class I creep, the relation to Q Mg should be discussed. 3,11,12) Sherby and Wadsworth 13) found that the activation energy at n = 2 was equal to about 135-139 kJ/mol while that at n = 3 was equal to about 137-142 kJ/mol in a fine grained Al-5%Mg-1.2%Cr alloy. They concluded that the slip process (dislocation creep) observed in the alloy including second phase particles was identical to that observed in Al-Mg solid solution alloys.…”

“…1) In Class I type alloys such as Al-Mg or Al-Cu base alloys, fairly large elongations have been observed at high temperatures even for coarse-grained samples. [2][3][4] It is recently called 'Class I superplasticity'. 5) This superplasticity has a merit of less cavitation because main deformation mechanism is not grain boundary sliding.…”