On the Residual Stress Control in Aluminum Alloy 7050

Escobar, Kurt A.; Gonzalez, B.; Ortiz, José Luis Luviano; Nguyen, Patrick; Bowden, D. M.; Foyos, J.; Ogren, J.; Lee, E.W.; Es‐Said, O.S.

doi:10.4028/www.scientific.net/msf.396-402.1235

Cited by 10 publications

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“…Validation against the computed room-temperature residual stresses is limited simply owing to the difficulty of measuring the internal strains and the high variability in the measurements. While some measurements are available for quenching [12] or welding [13], they remain rare, uncertain and usually are limited to one or two components of the stress tensor, and to the skin of the billet for as-cast materials [14][15]. In contrast to destructive methods for measuring residual stresses (hole-drilling strain gage, cut compliance, layer removal technique), physical methods such as neutron, X-ray or ultra-sound diffraction are very attractive [16] since they can yield all stress components.…”

Section: Introductionmentioning

confidence: 99%

Residual Stresses in As-Cast Billets: Neutron Diffraction Measurement and Thermomechanical Modeling

2012

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Stress relief treatment is often required prior to sawing aluminum DC cast products in order to prevent crack formation and significant safety concerns due to the presence of high residual stresses generated during casting. Numerical models have been developed to compute these residual stresses and yet have only been validated against measured surface distortions. In the present contribution, the variation in residual strains and stresses have been measured using neutron diffraction in two AA6063 grainrefined cylindrical billet sections cast at two casting speeds. The measured residual stresses compare favorably with the numerical model, in particular the depth at which the axial and hoop stresses change sign. Such results provide insight into the development of residual stresses within castings and show that the stored elastic energy varies linearly with the casting speed, at least within the range of speeds that correspond to production conditions. I IntroductionIn the fabrication of aluminum extrusion products, the first step is the semi-continuous casting of a cylindrical billet. The most commonly used process is known as direct chill (DC) casting [1]. This process gives rise to large thermally induced strains that lead to several types of casting defects (distortions, cold cracks, porosity, solidification cracking, etc.). During casting, thermally induced stresses are partially relieved by permanent deformation. When these residual stresses overcome the deformation limit of the alloy, cracks are generated either during solidification (hot tears) or during cooling (cold cracks). The formation of these cracks usually results in rejection of the cast part. Furthermore, thermally induced deformations can cause downstream processing issues during the sawing stage prior to extrusion, when the billet is cut without thermal annealing between casting and sawing. For large diameter and high strength alloys, sawing becomes a delicate task owing to the risk of saw pinching or crack initiation ahead of the saw. Parts might be ejected and injure people or damage the equipment. The computation of stresses during DC casting of aluminum alloys has been the scope of several studies since the late 90's [2-10] and is a well established technique nowadays. Many numerical models have allowed researchers to compute the ingot distortions and the associated residual stresses. The validation of these models was often done by comparing the computed and measured ingot distortions, e.g. the butt-curl [8] and the rolling face pull-in for rolling sheet ingots produced by DC [9] or electromagnetic casting [11]. Validation against the computed room-temperature residual stresses is limited simply owing to the difficulty of measuring the internal strains and the high variability in the measurements. While some measurements are available for quenching [12] or welding [13], they remain rare, uncertain and usually are limited to one or two components of the stress tensor, and to the skin of the billet for as-cast materials [14][15]. In ...

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Section: Introductionmentioning

confidence: 99%

Residual Stresses in As-Cast Billets: Neutron Diffraction Measurement and Thermomechanical Modeling

2012

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“…While some measurements are available for quenching [12] or welding [13], they remain rare, uncertain and usually are limited to one or two components of the stress tensor, and to the skin of round billets for as-cast materials [14][15]. In contrast to destructive methods for measuring residual stresses (hole-drilling strain gage, cut compliance, layer removal technique), physical methods such as neutron, X-ray or ultra-sound diffraction are very attractive [16] since they can yield all stress components.…”

Section: Introductionmentioning

confidence: 99%

Neutron Diffraction Measurement of As‐Cast Residual Stresses in AA7050 Rolling Plate Ingots: Influence of a Wiper

et al. 2014

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During casting, thermally induced deformations give birth to ingot distortions and residual stresses. For some high strength alloys, ingot cracking can happen during casting per se or during cooling down. Ingot distortions such as rolling face pull-in, but curl and but swell are rather easy to quantify as opposed to internal stresses. As aluminium is rather transparent to neutrons, residual stress measurements using neutron diffraction appeared to be a good way to validate the thermomechanical models aimed at simulating the stress build-up during casting. This technique has been applied to DC cast AA7050 rolling plate ingots with special attention to the stress generation in the transient start-up phase, i.e. in the foot of the ingot. Additional results using the hole drilling method complement the measurements. The measured stress distributions are compared with the results of a numerical model of DC casting for ingots cast with and without a wiper. I IntroductionIn the fabrication of aluminum rolling plates, the first step is the semi-continuous casting of a rectangular ingot. The most commonly used process is known as direct chill (DC) casting [1]. This process gives rise to large thermally induced strains that lead to several types of casting defects (distortions, cold cracks, porosity, solidification cracking, etc.). During casting, thermally induced stresses are partially relieved by permanent deformation. When these residual stresses overcome the deformation limit of the alloy, cracks are generated either during solidification (hot tears) or during cooling (cold cracks). The formation of these cracks results in rejection of the cast part. Furthermore, thermally induced stresses can cause downstream processing issues during the sawing stage prior to rolling. For large ingot formats and high strength alloys, sawing becomes a delicate task owing to the risk of saw pinching or crack initiation ahead of the saw. The use of wipers during casting largely reduces the level of as-cast stresses.The computation of stresses during DC casting of aluminum alloys has been the scope of several studies since the late 90's [2-10] and is a well established technique nowadays. Many numerical models have allowed researchers to compute the ingot distortions and the associated residual stresses. The validation of these models was often done by comparing the computed and measured ingot distortions, e.g. the butt-curl [8] and the rolling face pull-in for rolling sheet ingots produced by DC [9] or electromagnetic casting [11].Validation against the computed room-temperature residual stresses is limited simply owing to the difficulty of measuring the internal strains and the high variability in the measurements. While some measurements are available for quenching [12] or welding [13], they remain rare, uncertain and usually are limited to one or two components of the stress tensor, and to the skin of round billets for as-cast materials [14][15]. In contrast to destructive methods for measuring residual stresses (hole-drilli...

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“…While some measurements are available for quenching 12 or welding, 13 they remain rare, uncertain and usually are limited to one or two components of the stress tensor and to the skin of the billet for as cast materials. 14,15 In contrast to destructive methods for measuring residual stresses (hole drilling strain gage, cut compliance and layer removal technique), physical methods such as neutron, X-ray or ultrasound diffraction are very attractive 16 since they can yield all the stress components.…”

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confidence: 99%

Stored elastic energy in aluminium alloy AA 6063 billets: residual stress measurements and thermomechanical modelling

Drezet

Evans

Pirling

et al. 2012

International Journal of Cast Metals Research

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Stress relief treatment before machining and sawing aluminium direct chill cast products is required to avoid uncontrolled distortion, crack formation and significant safety concerns due to the presence of thermally induced residual stresses created during casting. Numerical models have been developed to compute these residual stresses and yet have only been validated against measured surface distortions. In the present contribution, the variations in residual strains and stresses have been measured using neutron diffraction and hole drilling strain gage in two AA 6063 grain refined cylindrical billet sections cast at two casting speeds. The measured residual stresses compare favourably with the numerical model, in particular the depth at which the axial and hoop stresses change sign. Such results provide insight into the development of residual stresses within castings and show that the stored elastic energy varies linearly with the casting speed, at least within the range of speeds that correspond to production conditions. Keywords: Aluminium billet casting, Residual stresses, FE modelling, Neutron diffraction, Hole drilling strain gage, Elastic energy IntroductionIn the fabrication of aluminium extrusion products, the first step is the semicontinuous casting of a cylindrical billet. The most commonly used process is known as direct chill (DC) casting.1 This process gives rise to large thermally induced strains that lead to several types of casting defects (distortions, cracks, porosity, residual stresses, etc.). During casting, thermally induced stresses are partially relieved by permanent deformation. When these residual stresses overcome the deformation limit of the alloy, cracks are generated during either solidification (hot tears) or cooling (cold cracks). The formation of these cracks usually results in rejection of the cast part. Furthermore, the thermally induced deformations can cause downstream processing issues during the sawing stage before extrusion, when the billet is cut without thermal annealing between casting and sawing. For large diameter and high strength alloys, sawing becomes a delicate task owing to the risk of saw pinching or crack initiation ahead of the saw. Parts might be ejected and injure people or damage the equipment.The computation of stresses during DC casting of aluminium alloys has been the scope of several studies since the late 1990s 2-10 and is a well established technique nowadays. Many numerical models have allowed researchers to compute the ingot distortions and the associated residual stresses. The validation of these models was often carried out by comparing the computed and measured ingot distortions, e.g. the butt curl 8 and the rolling face pull-in for rolling sheet ingots produced by DC 9 or electromagnetic casting. 11Validation against the computed room temperature residual stresses is limited simply owing to the difficulty of measuring the internal strains and the high variability in the measurements. While some measurements are available for quenching 12 or we...

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On the Residual Stress Control in Aluminum Alloy 7050

Cited by 10 publications

References 0 publications

Residual Stresses in As-Cast Billets: Neutron Diffraction Measurement and Thermomechanical Modeling

Residual Stresses in As-Cast Billets: Neutron Diffraction Measurement and Thermomechanical Modeling

Neutron Diffraction Measurement of As‐Cast Residual Stresses in AA7050 Rolling Plate Ingots: Influence of a Wiper

Stored elastic energy in aluminium alloy AA 6063 billets: residual stress measurements and thermomechanical modelling

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