Ce travail vise à analyser l'influence de la température, de la vitesse de déformation et de la durée de vieillissement sur le comportement mécanique de l'alliage EN AW 6016-T4, vieilli naturellement. Cet alliage a été sélectionné car il est couramment utilisé dans l'industrie automobile. Les essais mécaniques de traction ont été réalisés pour une gamme de température comprise entre la température ambiante et 300°C, pour différentes vitesses de déformation et à des temps différents après leur production. Les résultats constituent une nouvelle base de données expérimentale qui permettra d'évaluer les applications potentielles de la mise en forme à chaud de cet alliage

Laurent, Hervé

Menezes, Luis

Oliveira, Marta

Simoes, Vasco

I-Revues

22ème Congrès Français de Mécanique                                               Lyon, 24 au 28 Août 2015 
 
 
Influence of temperature, strain-rate and aging on 
the mechanical behaviour of an Al-Mg-Si alloy 
 
V.M. SIMÕESa,b*, H. LAURENTa, M.C. OLIVEIRAb, L.F. MENEZESb 
 
a. Université de Bretagne-Sud, EA 4250, LIMATB, F-56100 Lorient, France, 
 {vasco.simoes; herve.laurent}@univ-ubs.fr 
b. CEMUC, Dep. de Eng. Mec., Univ. de Coimbra Polo II,  
Pinhal de Marrocos, 3030-788 Coimbra, Portugal, {marta.oliveira; luis.menezes}@dem.uc.pt 
 
 
Résumé:  
 
Ce travail vise à analyser l'influence de la température, de la vitesse de déformation et de la durée de 
vieillissement sur le comportement mécanique de l’alliage EN AW 6016-T4, vieilli naturellement. Cet 
alliage a été sélectionné car il est couramment utilisé dans l'industrie automobile. Les essais mécaniques 
de traction ont été réalisés pour une gamme de température comprise entre la température ambiante et 
300°C, pour différentes vitesses de déformation et à des temps différents après leur production. Les 
résultats constituent une nouvelle base de données expérimentale qui permettra d’évaluer les 
applications potentielles de la mise en forme à chaud de cet alliage.  
 
Abstract:  
 
This work aims to analyse the influence of temperature, strain-rate and aging time in the mechanical 
behaviour of an EN AW 6016-T4 alloy, naturally aged. This Aluminium Alloy was select since it is 
commonly used in the automotive industry. Uniaxial tensile tests were performed within a temperature 
range between room temperature and 300ºC, for different strain rates and at different times after its 
production. The results collected constitute an experimental database for evaluating the potential 
application of warm forming processes to this alloy 
 
Mots clefs: Al-Mg-Si Alloys; Mechanical Characterization; Temperature; 
Strain rate; Aging 
 
1 Introduction  
 
The new milestones of societies comprise the reduction of pollution and Greenhouse gas, namely CO2. 
Herein the transport sector plays a crucial role, for which the use of recyclable and lighter materials can 
contribute to the energy cost reductions and, consequently, the ecological footprint. In this context, the 
Aluminium Alloys (AA) present a great benefit since they are light and highly recyclable materials, 
namely when compared with conventional steels [1-2]. However, they also present lower formability 
and higher springback when compared with conventional mild steels. Thus, a key challenge is the 
22ème Congrès Français de Mécanique                                               Lyon, 24 au 28 Août 2015 
 
improvement of AA formability in order to extend their applications. Herein the warm forming is a 
potential solution [3]. 
Numerous studies show the importance of temperature as a key parameter to improve formability and 
reduce springback. Toros et al. [4] presented a literature review on warm forming of Aluminum–
Magnesium alloys highlighting the use of a temperature range from 200°C to 300°C, to achieve 
improved formability and better surface quality of the final product. Further on 5xxx series, with 
AA5754, Laurent et al. [5] also showed that warm forming condition reduce flow stress and springback. 
Moreover, and also in AA5754, the warm forming can avoid the problems of dynamic strain aging 
(DSA) known as Portevin–Le Chatelier (PLC) effect present in 5xxx series at room temperature [6-7]. 
Concerning 6xxx series, although does not present the higher strength, it is commonly used too. Bolt et 
al. [8] and, Ghosh et al. [9] studied the warm forming of AA6016, concluding that warm forming offers 
a good possibility for drawing complex parts, which cannot be made at room temperature without extra 
forming operations. In the stretch-drawing of a rectangular conical shape, Bolt et al. [8] observed the 
best increase of the critical deep drawing ratio for a temperature of 175°C, within a range from room 
temperature to 250°C. In deep drawing of a cylindrical cup, Ghosh et al. [9] observed that, with the 
increase of temperature, the amplitude of earing decreases while the number of ears remains the same, 
indicating that the in-plane trend of the mechanical properties does not changes with temperature but 
becomes slightly more isotropic. Concerning the warm forming of AA5052 and AA6061 sheet alloys, 
Mahabunphachai and Koç [10] concluded that the change of grain size due to the effects of elevated 
temperatures and strain rates were not significant. Therefore, they concluded that the decrease in the 
flow stress at high temperature levels was mainly due to the thermally activated dislocation lines. In 
brief, warm forming conditions may reduce the flow stress and rate of work hardening, improving the 
material ductility and toughness.  
 
The Aluminium Alloy EN AW 6016-T4 is used in this study. This alloy is commonly used in the 
automotive industry. It is known as a Si excess alloy since Mg/Si ratio in mass fraction percentage 
[wt.%] is less than one. The EN AW 6016-T4 sheets were made and supplied by Constellium with a 
Mg/Si ratio equal to 0.19 [wt.%], and; were cold rolled up to 1mm thickness, annealed, quenched and 
natural aged (T4). The material received was solution treated on March 25th, 2014. The mechanical 
properties evaluated by uniaxial tensile tests performed with four days of maturations are presented in 
Table 1.  
 
Table 1 – Mechanical properties of EN AW 6016-T4 (supplier results). Rm tensile strength. Rp0.2 proof 
strength at 0.2% of the extensometer gauge length. Ag percentage of non-proportional elongation at 
maximum force. n4-6 strain hardening coefficient between 4 and 6 % of plastic elongation. n10-15 strain 
hardening coefficient between 10 and 15 % of plastic elongation (terms and definitions according with 
the European Standard EN 10002-1).  
Rm Rp0.2 Ag n4-6 n10-15 
198 MPa 88 MPa 24.6 % 0.32 0.27 
 
2 Experimental setup and procedure 
 
Uniaxial tensile tests were performed at temperatures ranging from room temperature up to 300°C and 
at strain rates ranging from 2x10-4s-1 up to 2x10-2s-1. The anisotropy was studied using specimens cut 
along three different directions in the sheet plane: 0°, 45° and 90° with the rolling direction. Tensile 
tests were performed with a 6 month time lag, to evaluate the influence of static strain aging. In this 
context, the first series of tensile tests were performed approximately 1 month after heat treatment and 
22ème Congrès Français de Mécanique                                               Lyon, 24 au 28 Août 2015 
 
the second series 7 months after. All tests were performed in a Gleeble 3500 electromechanical testing 
machine, which involves a closed loop system using direct resistance Joule heating, via a 50 Hz AC 
current. The strain fields were locally measured, in the specimens’ middle zone with 6mm width, by 
Digital Image Correlation (DIC) technique using ARAMIS 5M 3D optical system.  
A minimum of two tensile tests were performed for every condition under analysis (temperature, strain-
rate, anisotropy and aging time). The results were always reproducible, with an average scatter of true 
stress less than ±1MPa for the same value of true strain. Thus, in the following section only the result 
of one of the tests is presented. 
 
3 Results and Discussion  
 
Figure 1 presents the results of the uniaxial tensile tests performed for five different temperatures: 20°C 
(room temperature), 100°C, 150°C, 200°C and 300°C. The increase in temperature leads to a decrease 
of the yield stress and the ultimate stress. Although not shown here, the uniaxial tensile tests performed 
at different orientations to the rolling direction show that the material presents a negligible anisotropic 
behaviour of the yield stresses that does not change with temperature. 
Concerning natural aging, due to material storage, the 6016-T4 alloy reveals a variation of the 
mechanical properties with time. As shown in the same figure, the aging leads to an increase of the yield 
and ultimate stresses; the total elongation is reduced due to the aging effect. 
 
 
Figure 1 – Influence of aging on stress-strain curves obtained from uniaxial tensile tests performed 
at different temperatures, for specimens oriented along the rolling direction. 
 
A summary of the mechanical properties obtained from the nominal tensile test curve is presented in 
Table 2. The results correspond to the ones obtained at 1 month’s maturation. Regarding the percentage 
of total elongation at maximum force (Agt [%]), no significant variation is noticeable between 20°C and 
200°C, with a decrease at 300°C. The percentage of total elongation (At) shows a constants increase with 
increasing temperature between 20°C and 300°C, with the highest change occurring between 20°C and 
100°C. The tensile strength (Rm) presents a constant decrease with the increase of temperature. The 
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 0RD-20ºC-v1
 0RD-100ºC-v1
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22ème Congrès Français de Mécanique                                               Lyon, 24 au 28 Août 2015 
 
tensile test results are in agreement with the ones reported by Kurukuri [11]. The flow stress reduction 
and the increase of total elongation indicate that under non-isothermal conditions the limit drawing 
height of deep drawn components can be improved as reported by Bolt et al. [8] and Ghosh et al. [9]. 
 
Table 2 – Mechanical Properties of EN AW 6016-T4 (1 month’s maturation). Agt percentage of total 
elongation at maximum force. At percentage of total elongation. Rm tensile strength (terms and 
definitions according with the European Standard EN 10002-1). 
Temperature 20°C 100°C 150°C 200°C 300°C 
Agt [%] 24.82 22.02 24.02 27.54 14.48 
At [%] 40.32 49.61 51.84 53.92 57.79 
Rm [MPa] 217.97 192.90 173.18 156.22 73.23 
 
Figure 2 shows the stress-strain results of uniaxial tensile tests performed with three different values of 
strain rate: 2x10-4, 2x10-3 and 2x10-2s-1, for two different temperatures (20ºC and 200ºC). It is shown 
that the strain rate sensitivity increases with the increase of temperature. In fact, at room temperature 
EN AW 6016-T4 alloy is not sensitive to strain rate. However, at 200ºC the results clearly show that a 
decrease of the strain rate leads to a decrease of the yield stress. Also at 200ºC, the work hardening is 
affected by the strain rate; at 2x10-4s-1 the work hardening is initially high and saturates after a true strain 
of 0.05; at 2x10-3 and 2x10-2s-1 the EN AW 6016-T4 presents a constant and smooth evolution of work 
hardening. 
 
 
Figure 2 – Influence of strain-rate on stress-strain curves obtained from uniaxial tensile tests 
performed at different temperatures, for specimens oriented along the rolling direction 
 
4 Conclusions  
 
The main conclusions of this work are: the increase of temperature leads to a decrease of the yield and 
the ultimate stress; increasing natural aging time leads to an increase of the yield stress and the ultimate 
stress; the material presents a small orthotropic behaviour in the yield stresses that does not change with 
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22ème Congrès Français de Mécanique                                               Lyon, 24 au 28 Août 2015 
 
temperature; and, the strain rate sensitivity increases with the increase of temperature being null at room 
temperature and positive at 200°C. 
 
Acknowledgements 
 
This research work is sponsored by national funds from the French Ministry of Higher Education and 
the Portuguese Foundation for Science and Technology (FCT) via the project PTDC/EMS-
TEC/1805/2012 and by FEDER funds through the program COMPETE – Programa Operacional 
Factores de Competitividade, under the project CENTRO -07-0224 -FEDER -002001 (MT4MOBI). 
The authors are also grateful to Constelium for supplying the material to perform these experimental 
tests. The first author is also grateful to the FCT for the PhD grant SFRH/BD/90669/2012.  
 
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Influence of temperature, strain-rate and aging on the mechanical behaviour of an Al-Mg-Si alloy

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Influence of temperature, strain-rate and aging on the mechanical behaviour of an Al-Mg-Si alloy

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