Influence of microstructure on work-hardening and ductile fracture of aluminium alloys

Abstract

The effect of microstructure on the work-hardening and ductile fracture of aluminium alloys was studied using an experimental-numerical approach. Four aluminium alloys with different strength and particle content were tested in uniaxial tension after the following subsequent processing steps: 1) casting and homogenization, 2) extrusion, and 3) cold rolling followed by heat treatment. The latter processing step was carried out to obtain a recrystallized grain structure with random crystallographic texture. The alloys were two AlFe alloys with different Fe content, one AlMn alloy and one AlMgSi alloy. The grain structure, particle distribution and crystallographic texture were determined for all combinations of alloy and processing route using optical and scanning electron microscopy. Tensile tests were carried out on axisymmetric samples to obtain the true stressstrain curves to failure and the true failure strain of the materials, using a laser-based measuring system. Based on numerical simulations of the tensile tests, the equivalent stress-strain curves were determined to failure, assuming J 2 flow theory. The results showed that the microstructure had a marked effect on both work-hardening and ductility, while the ductile fracture mechanism remained unchanged. The plastic anisotropy, induced by the extrusion process and not entirely removed by the cold rolling and heat treatment, led to a wide range of fracture modes of the axisymmetric samples. The failure strain was markedly lower for the cast and homogenized material than for the extruded and the cold rolled and recrystallized materials of the same alloy. The failure strain was further found to decrease linearly with the yield stress for similar microstructure.

Simulation of large-strain behaviour of aluminium alloy under tensile loading using anisotropic plasticity models

“…The material was homogenized in a laboratory furnace using temperature-time cycles similar to the industrial practice, consisting of a soaking treatment followed by a predetermined cooling rate (see [40] for details). The ingot was subsequently extruded in an 800 tons laboratory press to rectangular profiles with dimensions 10×50 mm 2 using industrial extrusion parameters, i.e., billet temperature of 475°C, container temperature of 435°C and ram speed of 5 mm/s.…”

Modified TIG Welding Joint Process: An Approach to Improve Microstructure and Fracto-Mechanical Behavior by MWCNTs Inducement in Al-Mg-Si Alloy

“…The initiation of fracture has occurred from the center position by forming a large elliptical dimple in-between as highlighted in the figure. The shape of the fracture mode is exactly in resemblance with cup and cone type, though the cross section is rectangular (not circular) which grows with the same aspect ratio in longitudinal and transversely towards the periphery forming isotropic elliptical flow [43]. The presence of microvoids at distributed positions can easily be seen in Figure 13a.…”

Microstructure and mechanical properties of thin varying thickness strips with different transition zones produced by micro flexible rolling

“…41 They will always be found at the bottom of the ductile dimples, which are related to nucleation, growth and coalescence of voids at hard particles. 42 In fact, the voids will emerge by particle cracking (consisting of radius, shape and volume fraction), decohesion surrounding the constituent particles or pre-existing in the initial materials. 40,43,44 For all fractographs in this study, the fracture morphology of specimen 4 shows deeper and more uniform ductile dimples, gradually followed by specimens 3, 2 and 1, indicating that it has absorbed more stored energy during the plastic deformation of flexible rolling due to the smaller grain aspect ratio 30 and then achieved relatively better ductility.…”

“…Simultaneously, second phase particles or inclusions are the major factors in forming ductile dimples 41 . They will always be found at the bottom of the ductile dimples, which are related to nucleation, growth and coalescence of voids at hard particles 42 . In fact, the voids will emerge by particle cracking (consisting of radius, shape and volume fraction), decohesion surrounding the constituent particles or pre-existing in the initial materials 40,43,44 .…”