An Analysis of Strain Path Effects on Static Recrystallisation in Hot Worked Aluminium Alloy AA5052 Using Forward and Reverse Torsion

Abstract

The effects of strain path reversal, using forward and reverse torsion, on the microstructure evolution in the aluminium alloy AA5052 have been studied using high resolution electron backscatter diffraction. Deformation was carried using two equal steps of forward/forward or forward/reverse torsion at a temperature of 300°C and strain rate of 1s-1 to a total equivalent tensile strain of 0.5. Sections of the as-deformed gauge lengths of both test specimens were then annealed at 400°C for 1 hour in a salt bath in order to investigate their subsequent recrystallisation response. In both strain path histories the deformation substructure in the grains analysed consisted of microband arrays within an equiaxed dislocation cell structure. The material subjected to forward/forward deformation did, however, have a slightly greater number of low angle boundaries, i.e. boundaries < 15° misorientation, whilst the forward/reverse material had some grains containing little evidence of substructure. On annealing both materials had significantly reduced levels of low angle boundaries but only the forward/forward material had an increased number of high angle boundaries and a reduced grain size, indicating recrystallisation had only occurred in this material. This would suggest that the deformation microstructure within the forward/forward condition was sufficient to initiate and maintain recrystallisation whilst the microstructure produced by the forward/reverse test contained insufficient nuclei or internal energy to produce a recrystallised material within 1 hour. Further work is now required at different annealing times in order to determine if the major effect of strain path is on retarding nucleation, growth or both.

The Effect of Strain Path Reversal during Austenite Deformation on Phase Transformation in a Microalloyed Steel Subjected to Accelerated Cooling

“…2, upon strain reversal, a significant drop of the flow stress level was observed in specimen X2 comparing to the test X1 without strain reversal. This phenomenon known as Bauschinger effect has been widely reported for different types of polycrystalline metallic materials and is believed to be associated with the annihilation of dislocations with opposite signs after strain reversal [2]. In the present study, the difference between flow stresses is about 20MPa.…”

“…Previous studies have revealed that this strain path can affect the recrystallisation kinetics of stainless steels [1] and aluminium alloys [2] as well as the kinetics of spheroidisation of titanium alloys [3]. For microalloyed steels, it has been reported the strain reversal retards the recrystallisation and Nb(C,N) precipitation kinetics [4].…”