Mechanism of the Bauschinger effect in Al-Ge-Si alloys

Abstract

Wrought Al-Ge-Si alloys were designed and produced to ensure dislocation bypass strengthening ("hard pin" precipitates) without significant precipitate cutting/shearing ("soft pin" precipitates). These unusual alloys were processed from the melt, solution heat treated and aged. Aging curves at temperatures of 120, 160, 200 and 240°C were established and the corresponding precipitate spacings, sizes, and morphologies were measured using TEM. The role of non-shearable precipitates in determining the magnitude of Bauschinger was revealed using large-strain compression/tension tests. The effect of precipitates on the Bauschinger response was stronger than that of grain boundaries, even for these dilute alloys. The Bauschinger effect increases dramatically from the under-aged to the peak aged condition and remains constant or decreases slowly through over-aging. This is consistent with reported behavior for Al-Cu alloys (maximum effect at peak aging) and for other Al alloys (increasing through over-aging) such as Al-Cu-Li, Al 6111, Al 2524, and Al 6013. The Al-Ge-Si alloy response was simulated with three microstructural models, including a novel SD (SuperDislocation) model, to reveal the origins of the Bauschinger effect in dilute precipitation-hardened / bypass alloys. The dominant mechanism is related to the elastic interaction of polarized dislocation arrays (generalized pileup or bow-out model) at precipitate obstacles. Such effects are ignored in continuum and crystal plasticity models.

Analysis of the Bauschinger Effect in Cold Drawn Pearlitic Steels

“…The reduction of strength due to plastic pre-strain is a question of major relevance in various research and application areas. This finding furthered the advancements in the theory of the mechanical behaviour of materials in the plastic regime under cyclic loading [1,3,[8][9][10][11][12][13][14][15][16], as well as the technological innovations in cold plastic strain conforming processes [17][18][19][20]. On the one hand, deeper knowledge about the material mechanical response allows one to optimise the plastic strain conforming processes, avoiding excessive material damage in load reversals, and on the other, this facilitates more accurate predictions (e.g., from numerical simulations) of the performance of materials undergoing cyclic strain hardening.…”

Evolution of Young’s Modulus of Cold-Deformed Pure Aluminium in a Tension Test

“…These changes can be higher than 10% in some materials. This is not an important factor in material selection processes, but it has a decisive effect on conformation processes by plastic deformation [3][4][5][6][7][8][9][10][11][12] where the "springback ", the elastic-plastic recovery of the materials just after plastic deformation, is largely characterized. In this case, changes in Young's modulus are analysed, to apply in the modeling calculations of elastic recoveries.…”