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					                                                           18. ‐ 20. 5. 2010, Rožnov pod Radhoštěm, Česká Republika 




    INFLUENCE OF INITIAL SEMI-PRODUCT’S STRUCTURE ON FORMABILITY OF ALUMINIUM
                                  ALLOY EN AW 6056

     Pavel SOLFRONK a, Iva NOVÁKOVÁ b, Iva NOVÁ c, Jiří SOBOTKA d, Michaela KOLNEROVÁ e
                         Technical University of Liberec, Studentská 2, 46117 Liberec, CZ,
           a
               pavel.solfronk@tul.cz, b iva.novakova@tul.cz, c iva.nova@tul.cz , d jiri.sobotka@tul.cz,
                                            e
                                              michaela.kolnerova@tul.cz

Abstract

This paper deals with the monitoring the influence of structure onto formability of alloy EN AW 6056. For
experimental evaluation of formability was used upsetting test. From measured results of such test were
determinate basic values of formstrength, deformation ratio, logarithmic degree of deformation and
deformation work. For upsetting were used samples with diameter 20mm and height 29mm. One cylindrical
semi-product designed for experiment for prepared by rolling and another one was casted.

1.      INTRODUCTION
Formability of metals and their alloys is technological property which evaluates material ability to its plastic
deformation. Such property is conditional and depends on physical quantities like are forming material
temperature and strain rate. Ability of aluminium and its alloys to plastic deformation is closely connected
with cubic crystalline structure – face centered system. In such system during deformation take place 12 slip
planes which contribute for good plastic deformation. With increasing loading also increase number of slip
planes and thus are formed whole deformation bands. With regard to still increasing portion of parts
produced from aluminium alloys is to this problem necessary to pay more attention. Nowadays deals with the
problem about aluminium alloys formability site of Department of Engineering Technology on Faculty of
Mechanical Engineering TU of Liberec in the frame of solving grant project GAČR 101/09/1996. “Influence of
material structure on aluminium alloys formability”.
Plastic deformation of metals is result of external forces loading which induce such material state of stress
which is higher than yield strength and lower than ultimate strength. Due to this loading are induced
permanent dimensions changes or more precisely material shape. For fixed volume are such changes
increasing with increasing plastic deformation degree. For small deformation degree is not possible by outer
study to observe any changes and their courses which goes with metal plastic deformation. Under normal
temperature and low loading rate is plastic deformation accompanying by slip which is created in different
number of slip planes. Despite of theoretical presumptions was found out that slip firstly takes place only in
certain planes and certain directions. Generally is true that slip firstly takes place in planes and directions
which contains the most atoms. At aluminium and its alloys it represents 12 slip planes (4 planes of type
{111} and 3 directions <101>). Great number of slip planes causes excellent plastic deformation of pure
aluminium and its alloys [3]. Aluminium alloys which are created by solid solution exhibits very high
formability and thus also ability for permanent plastic deformation. Reversely formability of aluminium alloys
with heterogeneous structure is worse. Aluminium alloys at which are due to alloying created intermedially
phases have difficult formability. Formability under cold forming of aluminium and especially aluminium alloys
is influenced by hardening. The best formability under cold forming exhibits pure aluminium and alloys of
type AlMn and AlMgSi. Therefore is better to carry out hot forming. Same very important quantity for metal
forming is formstrength value or more precisely formresistance. Formresistance is defined like stress in the
movement forming tool direction onto plane of projection. In principle it is material response onto loading
                                                          18. ‐ 20. 5. 2010, Rožnov pod Radhoštěm, Česká Republika 



from outer forming force. There are valid very simplified dependences σ ≈ f (ε), ko ≈ f (ε) or        ko ≈ f (φ.).
Formresistance values are given in dependence on relative deformation or logarithmic degree of
deformation. Formresistance is not constant for certain metal but dependences on mechanical material
properties, temperature-speed forming conditions, state of stress, structure, friction and so on. With regard to
aluminium alloy type, its previous processing and type of forming machine can values of formstrength varies
from 80 to 250 MPa [1].

2.     FORMABILITY EXPERIMENTAL MEASUREMENT FOR ALUMINIUM ALLOYS

2.1.   Static tensile test
In connection with aims of solving grant project GAČR 101/09/1996 were carried out experiments in order to
monitor formability of chosen aluminium alloys. For this purpose was already chosen alloys EN AX 6056 in
the formed tubes form Ø 50 x 500 mm. Samples were divided into two groups. In the first case was this tube
melted and subsequently continuously casted into mould and thus was make several casts with cylindrical
shape Ø 50 x 150 mm. From these casts were prepared several samples for static tensile test. In the second
case were testing samples for static tensile test machined right from material semi-product AA 6056.
Measured average values of basic material characteristics for both cases are given in table 1. Graphical
expression of static tensile test course is clearly shown in fig. 1. Static tensile test was carried out on device
TIRAtest 2300 which is already placed on workplace KSP – FS, TU of Liberec.



Table 1 . Average values of used aluminium alloys mechanical properties

                                                   Values of mechanical properties
Aluminium alloy type                        Rm [MPa]           Rp0,2 [MPa]                  A50mm [%]
AA 6056                                      432,3                277,6                       19,3
AA 6056 melted and casted                    127,1                105,4                       1,83
into mould




                             Fig. 1. Graphical expression of static tensile test course

2.2.   Upsetting test

To monitor formability of alloy EN AW 6056 was used upsetting test. For this test were produced testing
samples with Ø 20 x 29 mm. Such testing samples dimensions are according to ČSN 42 0426. Forming, or
more precisely upsetting, was carried out on hydraulic forming press CBA 300/63. Forming force course in
dependence on ram movement was recorded by means of strain-gauge force sensor on PC. This course
                                                                   18. ‐ 20. 5. 2010, Rožnov pod Radhoštěm, Česká Republika 



represented initial data for calculation other values. Experiment was divided into 4 groups which are because
of lucidity given in table 2. In fig. 2 is shown measuring device and part of toll with specimen showing forming
of testing samples from aluminium alloys.


Table 2. Overview of performed experiments


        Group of                     Alloy                 Size of testing        Forming          Maximal force
       experiments                EN AW 6056                  sample            temperature        during forming
                                                                                    [°C]                 [N]
             1.                 Formed material             20 x 29 mm               20               363069
             2.                 Formed material             20 x 29 mm              200               312765
             3.                 Casted material             20 x 29 mm               20               217821
             4.                 Casted material             20 x 29 mm              200               217391

       a)                                       b)                                        c)




             Fig. 2. a) measuring device, b) upsetting of formed material, c) upsetting of casted material

2.3.     Equation for logarithmic deformation calculation
For strain evaluation of alloy En AW 6056 was like basic parameter observed logarithmic degree of
deformation. If upsetting is consider onto infinitely low length Δh, relative upsetting dφ = dh/h will be infinitely
low. Logarithmic degree of upsetting can be calculated from equation:

            h0
ϕ = ln         ,                                                                                             (1)
            h
where:              h0 –        initial height of formed sample,
                    h–          height of sample after forming.



2.4.     Formresistance calculation

For calculation formresistance can be used equation [6]:
                         dS
ko stř = k P .(1 + μ .      )                                                                                (2)
                         h
where:              μ–          friction coefficient (μ = 0,15);
                    dS –        instantaneous diameter of testing sample;
                    h–          instantaneous sample height.
                                                         18. ‐ 20. 5. 2010, Rožnov pod Radhoštěm, Česká Republika 



Based on measured course of forming forces and with the help of equations (1) and (2) were calculated
values of strain and formresistance. From these quantities were make graphs where formresistance is
depending on logarithmic deformation under certain temperature–speed forming conditions. Measured
values were subsequently approximated by Swift-Krupkowsky equation [2]:

σ = C.ϕ n ,                                                                                        (3)
where:          σ–     stress;
                C–     monotone hardening modulus;
                φ–     logarithmic degree of deformation;
                n–     deformation hardening exponent.
Values of constants from approximation for individual types of semi-products and subsequent forming
conditions are shown by means of graphs in fig. 3.




                Fig. 3. Dependences of formresistance on logarithmic degree of deformation

2.5.   Structure evaluation

In the frame of research was also monitored structure for both types of formed materials. For this purpose
was used light microscope Neophot 21 (producer Carl Zeiss Jena – GER). For etching was used 0,5% HF. In
fig. 4 are shown scratch patterns of both tested materials. Fracture area appearance was taken by means of
electron microscope Vega – frames are given in fig. 5.
                                                        18. ‐ 20. 5. 2010, Rožnov pod Radhoštěm, Česká Republika 




                       a)                                             b)
         Fig. 4. Alloy EN AW 6056 macrostructure, a) formed semi-product, b) casted semi-product




                       a)                                              b)
          Fig. 5. Alloy EN AW 6056 fracture area, a) formed semi-product, b) casted semi-product


3.    CONCLUSION
To monitor formresistance of materials designed for solid forming is important appropriate measuring device
which is able to record values of requisite quantities and based on such values can be carried out
formresistance calculation of formed material. Experimentally was proved that formresistance is complex
material property, depends on material type, on its chemical composition, structure, temperature,
deformation degree, strain rate, state of stress and friction. Another very important parameter is initial state
of forming material. Re-formed aluminium alloys EN AW 6056 supplied in the status T6 exhibited under cold
forming formresistance 732 [MPa] at logarithmic deformation ration 0,693. Under temperature forming 200°C
was formresistance of forming aluminium alloy 644 [MPa] at logarithmic deformation ration 0,742. Pre-casted
aluminium alloy EN AW 6056 had lower value of formresistance, however there was not any difference
between material formed under 20°C and 200°C. Under temperature 20°C was formresistance of alloy 426
[MPa] and under temperature 200°C was 425 [MPa] at logarithmic degree of deformation 0,742. Almost the
                                                                   18. ‐ 20. 5. 2010, Rožnov pod Radhoštěm, Česká Republika 



same values of formresistance for pre-casted alloy semi-product can be explained by crystalline structure or
material porosity. Material constant C and n are for subsequent semi-product forming under temperature
20°C: C = 758 [MPa] and n = 0,174. For forming under temperature 200°C: C = 671 [MPa] and n = 0,164.
For subsequent forming of pre-casted semi-product under temperature 20°C: C = 456 [MPa] and n = 0,28
and under temperature 200°C: C = 452 [MPa] and n = 0,29.

ACKNOWLEDGEMENTS

                   This paper was written in support of grant project GAČR 101/09/1996.

LITERATURE

[1]   PETRUŽELKA, J.: Teorie tváření [Skripta]. FS, VŠB - TU Ostrava 2006.
[2]   MICHNA, Š. a kol.: Encyklopedie hliníku. 1. vyd. Prešov 2005.
[3]   PÍŠEK, F. et al.: Nauka o materiálu I. [1. svazek – Obecná nauka o kovech]. 2. rozšířené a přepracované vydání. Praha 1973.
[4]   SEDLÁČEK, V.: Neželezné kovy a slitiny. 1. vyd. Praha 1979.
[5]   DRASTÍK, F.: Výpočty v oboru kování a lisování. 1. vyd. Ptaha 1972
[6]   TMĚJ, J., MIKEŠ, V.: Teorie tváření. FS - TU Liberec 1995.
[7]   GONTARZ, A., WEROSKI, W.: Forging of aluminium alloys. Technological and theoretical aspects, Edited by Lublin Univ. of
      Technology, Lublin 2001 (in Polish).
[8]   TECHNICKÉ PODKLADY - firma Alcan Extrusion, Děčín, a.s. (Czech Republic).

				
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