Particle-Stimulated Nucleation of Recrystallization for Grain-Size Control in 01420 Al-Li Alloy

Materials Science and Technology

et al. 2011

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.

Section: Resultsmentioning

confidence: 95%

“…3a, which has been reported to be easily deformed to small pieces when rolled. 20 Their fracture may increase the number of microcracks which gradually grow and then join to fracture. It can be seen in Fig.…”

Section: Resultsmentioning

confidence: 99%

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

Materials Science and Technology

et al. 2011

“…Statistics shows that the grain structure on the ND-RD plane is similar to that on the ND-TD plane, resulting in a three-dimensional average grain size of 8?1 mm in the SL and 10?8 mm in the CL for the best candidate process, which is superior to that produced by single aging treatment followed by rolling and recrystallisation. 11 In addition to the grain sizes, the proportions of the CL produced by the two candidate processes in this investigation are also smaller.…”

Section: Layered Grain Structurementioning

confidence: 81%

“…Cui et al [8][9][10] successfully grain refined 1420 Al-Mg-Li alloy by TMP in order to induce superplasticity. Zhang et al 11,12 investigated the effects of single overaging temperatures and time on grain size of 1420 Al-Mg-Li alloy. In particular, recent studies found that a two-step, low-high temperature overaging treatment resulted in a desirable size and distribution of precipitates and an improvement of the surperplastic performance in 6xxx 13,14 and 1420 (Ref.…”

Section: Introductionmentioning

confidence: 99%

Effect of two-step aging on recrystallised grain size of Al–Mg–Li alloy

Materials Science and Technology

et al. 2011

A two-step overaging treatment was exploited in thermomechanical processing for producing fine grained Al–Mg–Li alloy sheets. The effects of each step and temperatures of overaging on the distribution of precipitates and recrystallised grain structure were investigated. The influence of preheating treatment before rolling on precipitate coarsening or dissolution was also considered. The results showed that, in contrast to rod shaped precipitates produced by single overaging at 300°C, precipitates produced by a two-step overaging tended to have globular morphologies. The globular precipitates were not deformed during the following large rolling reductions. Overaging at 200°C for 24 h then at 300°C for 24 h resulted in a distribution of globular precipitates with sizes of 1·0–1·2 μm. Preheating at 400°C or raising the overaging temperatures of each step to 300 and 400°C led to a reduction in the precipitate size. Subsequent rolling and recrystallisation resulted in a fine grain structure with an average grain diameter of approximately 8·1 μm for 200°C/24 h+300°C/24 h and 9·2 μm for 300°C/24 h+400°C/24 h overaging treated material respectively in the surface layers of the sheet.

Formation mechanism of gradient-distributed particles and their effects on grain structure in 01420 Al-Li alloy

J. Cent. South Univ. Technol.

et al. 2008

Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization. The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness. The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffractometry(XRD). The formation mechanism of the gradient particles was discussed. The results show that after aging, a gradient distribution of large particles along the thickness is observed, the particles in the surface layer(SL) are distributed homogeneously, whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction, and the volume fraction of the particles in the SL is higher than that in the CL. Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL, which is the main reason for the formation of layered grain structure along the thickness in the sheets.