Superplasticity of Al–Mg–Li alloy prepared by thermomechanical processing

Abstract

Grain refinement of Al–Mg–Li alloys for superplasticity prepared by thermomechanical processing has been a difficult task due to the cracking of these alloys when rolled at low temperatures. Raising the rolling temperature resulted in enhanced rollability of these sheets with no cracks but very coarse grains after recrystallisation. To solve this problem, a cross rolling schedule was developed to hinder fracture and simultaneously provide enough stored energy for following recrystallisaiton coupled by lowering the reheating temperature. Fine, equiaxed grains of ∼7 μm was achieved by this new approach and maximum total elongation of about 915 was obtained when deformed at a temperature of 525°C and an initial strain rate of 1×10−3 s−1.

Superplastic behavior of an Al–Mg–Li alloy

“…1(a)), rolling at a high starting temperature coupled with a cross-rolling after 55% rolled, produced the sheets with slightly edge fracture. At the same time, deformation zones around the precipitates formed by this rolling method were enough for the subsequent development of a fine grain structure by particle stimulated nucleation (PSN) due to the increased stored energy by lowering the re-heating temperature [9]. Following TMP ( Fig.…”

“…However, it was hard to use TMP consisting of cold or warm rolling to produce fine-grained Al-Mg-Li alloy sheets because of their poor workability at low temperatures that led to a premature fracture under working conditions [5,7]. Fortunately, a unique rolling method which used a high starting rolling temperature and a crossrolling method successfully prevented cracking of the sheets, and simultaneously fine grain structure of about 7 m was achieved by exploiting this rolling method in a novel TMP [9]. While studies of grain refinement and superplasticity of Al-Mg-Li alloy 1420 prepared by severe plastic deformation (SPD), such as equal-channel angular (ECA) pressing [1][2][3][4]10,11] and high-pressure torsion processing [12], were reported, there is no systematic investigation to be reported on the superplastic behavior of this alloy prepared by TMP.…”