Influence of pre-compression on the ductility of AA6xxx aluminium alloys

Abstract

Reversed loading experiments were conducted to study the influence of pre-compression on the ductility of three aluminium alloys. Diabolo-shaped specimens were machined from extruded profiles along the transverse direction (TD), and heat treated to peak strength (T6 temper). The specimens were subjected to five different levels of precompression (0%, 10%, 20%, 30%, 40%), i.e., the specimens were first compressed to a prescribed strain and then pulled to fracture in tension. Using a laser-based measuring system, the minimum diameter in the extrusion direction (ED) and thickness direction (ND) were continuously measured during the tests until fracture. The three aluminium alloys AA6060, AA6082.25 and AA6082.50 had different grain structure and texture. The AA6060 and AA6082.50 alloys had recrystallized grain structure with equi-axed grains and large elongated grains, respectively. The AA6082.25 alloy had a non-recrystallized, fibrous grain structure. It was found that pre-compression has a marked influence on the ductility of the aluminium alloys, which depends on the microstructure and strength of the alloy. Using the compressed configuration as the reference configuration, the relative failure strain could be calculated. For the AA6060 alloy, the relative failure strain increased for increasing pre-compression, and was approximately doubled for 40% pre-compression compared to pure tension. For the AA6082.25 alloy, a slight increase in the relative failure strain was observed for increasing pre-compression, while for the AA6082.50 alloy the

Nano-scale characterisation of sheared β” precipitates in a deformed Al-Mg-Si alloy

“…All of the observed precipitates were consistent with the β″ phase, except for relatively few inhomogeneously nucleated precipitates that were of an over-aged character. The material has an equiaxed grain structure with a strong cube texture and minor Goss components 32,33 .…”

Anisotropic Plasticity and Fracture of Three 6000-Series Aluminum Alloys

“…Continuous measurements of the force and diameters at the minimum cross-section were provided to fracture [23]. Measurements of the force F were obtained directly from the load cell, while the diameter measurements were acquired using a high-speed, contact-less AEROEL XLS13XY laser gauge with a resolution of 1 µm [3,23]. The laser gauge creates two perpendicular laser beams, each measuring 13 mm × 0.1 mm, which are pointed towards the detectors on the opposite side of the specimen.…”

“…In the cast and homogenized condition, the alloys typically have an equi-axed grain structure and random texture [1,2], which make the materials isotropic. However, after processing, the texture is altered [2,3] and the alloys develop anisotropic plasticity and fracture.…”

“…The size and shape of the grains are also of importance. In general, a small grain size is preferable for ductility [3,10]. In the work by Lohne and Naess [10] it is indicated that in some alloys, voids nucleate at particles on the grain boundaries due to the weaker precipitate free zones, and that these voids grow and further coalesce into cracks that propagate along the grain boundaries.…”

“…The third type of anisotropy is the topological anisotropy, which comes from the spatial distribution of constituent particles. Constituent particles typically break up and align in stringer-type clusters along the processing direction during rolling or extrusion [3,7,12]. Both the spacing between the particles within one cluster and the spacing between clusters are of importance for void coalescence [7,13].…”