Effect of pre-stretching on the mechanical behaviour of three artificially aged 6xxx series aluminium alloys

In order to improve the understanding of hot tearing during laser welding of aluminium alloys, the rheology of the alloys in the mushy state must be characterized. The present work investigates the mechanical behaviour of the aerospace alloy AA6056 using a specially designed isothermal tensile test in the mushy state. Using a Gleeble thermo-mechanical machine, two different tests have been performed: i) tests during partial remelting and ii) tests after partial solidification at a high cooling rate. These tests have been carried out not only on the 6056 alloy but also on a mix between 6056 and 4047 Al-Si alloy which corresponds to the composition of the nugget of a laser using a filler wire. The increase of the solid fraction results in an increase of the maximum stress and a change on the fracture surface from a smooth dendritic to a more ductile one. Moreover, the alloys exhibit a typical visco plastic behaviour with an increase of the maximal stress with the strain rate. When the test is performed at a particular solid fraction of 0.97, the fracture is more erratic and the ductility is low. The results show the existence of a ductile/brittle/ductile transition with the fraction of solid. The fracture stress is shown to be higher when testing after partial remelting as compared to partial solidification for the same solid fraction. This is due to the difference in microstructure of the mushy zone and more particularly in the connectivity of the solid skeleton. An adapted creep law is used to describe the mechanical behaviour of alloys during the partial remelting test using the fraction of grain boundary wetted by the liquid given by Wray. This law is shown to be irrelevant to the partial solidification tests, as a result of the modified geometry of the liquid phase. From these tests, we have determined a new law relating the solid fraction to the fraction of grain boundaries wetted by the liquid. This law is a useful tool to predict the mechanical behaviour when mechanical loading occurs during solidification.

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Effect of TIG Welding Process Parameters on Tensile behavior of 5XXX and 6XXX series Aluminium Alloys: A Review

Research Journal of Engineering and Technology ◽

10.5958/2321-581x.2018.00001.6 ◽

2018 ◽

Vol 9 (1) ◽

pp. 1

Author(s):

Abhi Bansal ◽

B.S Pabla ◽

S.C Vettivel

Keyword(s):

Process Parameters ◽

Aluminium Alloys ◽

Welding Process ◽

Tensile Behavior ◽

Tig Welding ◽

6Xxx Series

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STUDIES ON AGE HARDENING FOR IMPROVEMENT OF 6261 AND 6060 EXTRUDED ALUMINIUM ALLOYS

International Journal of Modern Physics B ◽

10.1142/s0217979210064757 ◽

2010 ◽

Vol 24 (15n16) ◽

pp. 2255-2260

Author(s):

KA KI (KATIE) AU ◽

MICHAEL HODGSON ◽

TIMOTIUS PASANG ◽

YU LUNG CHIU

Keyword(s):

Aluminium Alloys ◽

Extrusion Process ◽

Magnesium Silicide ◽

Age Hardening ◽

Precipitate Size ◽

Β Phase ◽

Heat Treated ◽

Series Alloy ◽

Main Components ◽

6Xxx Series

The magnesium silicide precipitates in the 6XXX series alloy are the main components contributing to the heat treatable properties and T6 strength of the alloy, which is influenced by the size, morphology and distribution of this phase. During the extrusion process, the strength contributing phase, magnesium silicide is supposed to dissolve and form again in a controlled state during age hardening. Whereas the intermetallic AlFeSi phase has little if any influence on the strength, the β phase of this intermetallic is known to cause brittle fracture of this alloy, as opposed to the less detrimental, more equiaxed α phase formed during homogenisation. This study investigates the as-extruded 6060 and the more heavily alloyed 6261 aluminium alloys, as well as the subsequent heat treated forms to investigate the ageing conditions to optimise hardening and shorten age hardening times for higher cost effectiveness. The microstructure, texture and precipitate size and distributions were studied using optical microscopy, SEM, EBSD and DSC. SEM and EDAX results have indicated signs of evenly distributed α AlFeSi and β Magnesium Silicide precipitates. The phase responsible for hardening is believed to be the much smaller scaled β" magnesium silicide, requiring much higher resolution studies.

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The Effect of Pre-Ageing and Addition of Copper on the Precipitation Behaviour in Al-Mg-Si Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.519-521.543 ◽

2006 ◽

Vol 519-521 ◽

pp. 543-548 ◽

Cited By ~ 14

Author(s):

A.I. Morley ◽

M.W. Zandbergen ◽

Alfred Cerezo ◽

George D.W. Smith

Keyword(s):

Aluminium Alloys ◽

Deleterious Effect ◽

Atom Probe ◽

Artificial Ageing ◽

Strengthening Effect ◽

Natural Ageing ◽

Aged Material ◽

3 Dimensional ◽

Precipitation Behaviour ◽

6Xxx Series

Hardness measurements and 3-dimensional atom probe analysis have been used to characterise the precipitation behaviour in two 6xxx series aluminium alloys, one Cu-free alloy (Al-0.78at%Mg- 0.68at%Si) and one Cu-containing alloy (Al-0.78at%Mg-0.68at%Si-0.30at%Cu). The heat treatments consisted of either natural ageing or pre-ageing at 353K followed by a paint-bake treatment at 453K. Natural ageing was seen to increase the hardness, and hence reduce formability compared to pre-ageing. In addition, the strengthening effect of artificial ageing was less after natural ageing than after pre-ageing. In the Cu-free alloy, needle-like β″ was observed to form only after a pre-ageing treatment during the first 60 minutes of a paint-bake treatment. In the Cucontaining alloy, needle-like β″ formed during paint bake in both the naturally-aged and pre-aged material, although it is formed more rapidly after pre-ageing. This was accompanied by an increase in strength over the Cu-free alloy and indicates that Cu reduces the deleterious effect of natural ageing.

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