az31
TRANSCRIPT
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Dipl.‐Ing. Jakob Hilgert
Institute of Materials Research
Materials Mechanics and Joining
Solid‐State Joining Processes (WMP)
Geesthacht20/03/2012
[afrin]
Review:
Friction Stir Welding Magnesium AZ31
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Content
Introduction FSW of Magnesium AZ31 Magnesium Alloy Material Properties after FSW Process Parameters Process Temperature Defects Failure Mode Dissimilar Welds References
AZ31, 355rpm‐160mm/min.
[johnson]
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Joining of magnesium alloys by conventional techniques is very difficult due to
the several problems such as, cracking, expulsion and void in the weld Zone [1], a
large heat affected zone (HAZ), porosity, evaporative loss of the alloying
elements and high residual stresses [2]
FSW is capable of joining magnesium alloy without melting* it and thus can
eliminate problems related to the solidification
FSW of Magnesium
*) The possibility of local melting is being discussed
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AZ31
[Carter]
0.2
‐
Mn [wt%]
Bal.13AZ31B
Bal.13AZ31
MgZn [wt%]Al [wt%]Alloy
The commercial AZ31B sheet material is used in most investigations. Nominal compositions given below:
Examples for applications of hot blow formed AZ31B sheet material. It is in the automotive industry due to the high weight saving potential
[Carter]
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AZ31
Example: base material microstructure of the magnesium wrought alloy AZ31B
[Noster]
rolling direction
thickness direction
Grain size: inhomogeneous
Mean: 11µm
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Material Properties after FSW‐grainsize‐
Properties of Friction Stir Welded AZ31 Magnesium alloy are reported controversially in literature. Afrin et. al. [1] have compiled results of various authors stating that the grain size of Friction Stir welded AZ31 can either be observed to grow [9] or to shrink [8] as compared to the base material.
[commin]
13mm shoulder
10mm shoulder
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Material Properties after FSW‐microhardness‐
The micro‐hardness is reported to increase by some [8] and to decrease by others [10]. The effect of FSW parameters on the material is also discussed controversially.
[Wang]
[Satoshi]
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Material Properties after FSW‐tensile strength‐
Weld4.0 201 124 AZ31, FSW
Weld 3.5 201 127 AZ31, FSW
10.0 292 205 AZ31, parent
6.5 288 219 AZ31, parent
15 290 220 AZ31‐H24, typical
12 255 200 AZ31, typical
Fracture locationElongation [%]Ultimate Stress [MPa]Proof Stress [MPa]Sample
Johnson et. al. [4] report tensile properties of AZ31 FSW welds as compared to the base material
69% ‐ 79% 23% ‐ 61%
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Material Properties after FSW‐tensile strength‐
base material
weld
[satoshi]
[Wang]
Some Authors [11] report a decrease of tensile strength of the weld with increasing welding speed while others [12] find no such effect. Even increasing tensile strength with increasing welding speed has been reported [8, 13]
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Material Properties after FSW‐parameter sensitivity‐
The diversity of these results suggests a strong dependency of the material properties on the whole welding setup.
Global statements do not seem to be readily available. This is in good agreement with the statements of Mishra et. al. [6] in the magnesium related part of their review on FSW and FSpW.
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Process Parameters
Johnson et. al. [4] state that the processing parameters of magnesium using FSW are found to be lower than those known for aluminium. This is attributed to the close packed hexagonal structure of the magnesium with its limited slip systems.
Additionally sticking of material to the tool (coated and uncoated) is reported to cause defects on the weld surface.
fcc
(Aluminium)
hdp
(Magnesium)
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Process Parameters‐process window‐
A process window has been suggested for 2mm thick plates by Commin et. al. [2]. Welding speeds V above 200mm/min and rotational speeds W of
are needed to achieve sound welds. The quality of these welds is improved with increasing load, welding speed and rotational speed.
mmmin rpm 4000
VW 2
2
Rotational speeds of 250 to 2500 rpm and welding speeds of 60 to 450 mm/min are reported in literature [6]
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Process Temperature‐Measurements‐
[commin]
Temperature Measurements and analytical fits are available for many process parameters.
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Process Temperature‐Modeling‐
The relationship between process parameters (V=welding speed and W=rotational speed) and the nugget temperature T has been reported by Commin et. al. [2]. A model developed by Abregast et. al. [14] was used to find:
With the empirical constants K=0.8052 and alpha=0.0442. Tm is the alloy melting point assumed at 610°C [15].
4
2
10VWK
TT
m
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Defects
[zhang]
The defects in a weld at different welding speeds. The white arrow is directed to the welding line at the bottom of the weld.
40mm/min 200mm/min
250mm/min 600mm/min
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Defect Model
Zhang et.al. [7] have proposed an analytical model based on the welding pressure to predict defect free welds:
When the welding pressure P and the rotational speed vr are kept at a constant value, the welding speed vw must be less than a material specific value α to avoid the formation of pores.
When the welding speed is kept constant, the welding pressure and the rotational speed must larger then a specific value.
!! rate
w
r rPvvP
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Failure Mode
Afrin et. al. [1] report that the majority of the welded tensile specimens fracture in the boundary region between the stir zone and the TMAZ. The failure mode is 45° shear fracture. This is explained by the grain growth and the presence of oxides on the fracture surface. Both dimple and cleavage like fracture are reported. This is in good agreement with results from Sunggon et. al. [5] which additionally report the fracture to occur predominantly on the advancing side of the weld.
[afrin]
[sunggon]
base material
Friction Stir Welded
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Failure Mode
[commin]
Typical fractography of friction stir welds failure (1000 rpm, 200 mm/min)
oxides
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Dissimilar Welds
When welding AZ31 to other magnesium alloys Johnson et. al. [4] found that it has a positive influence to place the AZ31 on the retreating side of the weld.
Dissimilar welds of AZ31 to AA6040 aluminium alloy have been reported by Satoshi et. al. [10] and recently by Kostka et. al. [3]. The AZ31 is place on the retreating side of the weld here as well.
AZ31
AZ31 Mg Alloy
Al Alloy
AS RS
AS RS
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Dissimilar Welds
[kostka]
Figure 2. Secondary electron micrograph of the AA6040 Al alloy and AZ31 Mg alloy interface: (a) AZ31 Mg alloy inclusion incorporated in the AA6040 Al alloy and surrounding intermetallic phase formation and (b) more detailed view of the intermetalliccompound formed.
Figure 1.Montage of backscattered electron micrographs of the crosssection (shoulder flow arm) of the friction stir zone (Advancing side of the tool is on the right in the AZ31 alloy).
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Dissimilar Welds
It is suggested that the intermetallic phase found at the joining interface are formed in a very complex process wherein the dominant mechanism has not yet been revealed.
[kostka]
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References
[1] N. Afrin, D.L. Chen, X. Cao, M. Jahazi, Materials Science and Engineering A 472 (2008) 179–186
[2] L. Commin, M. Dumont, J.‐E. Masse, L. Barrallier, Acta Materialia 57 (2009) 326–334
[3] A. Kostka, R.S. Coelho, J. dos Santos and A.R. Pyzalla, Scripta Materialia 60 (2009) 953–956
[4] R. Johnson, P. Threadgill, Magnesium Technology 2003 Edited by Howard I. Kaplan TMS (The Minerals, Metals & Materials Society), 2003
[5] L. Sunggon, K. Sangshik, L. Chang‐gil, Y. Chang Dong, and K. Sung Joon, Metallurgical And Materials Transactions A 36A, (2005), pp. 1609‐1612.
[6] R.S. Mishra, Z.Y. Ma, Mater. Sci. Eng. R 50 (2005) 1–78.
[7] H. Zhang, S.B. Lin, L. Wu, J.C. Feng, Sh.L. Ma, Materials and Design 27 (2006) 805–809
[8] X.H. Wang, K.S. Wang, Mater. Sci. Eng. A 431 (2006) 114–117.
[9] W.B. Lee, Y.M. Yeon, S.B. Jung, Mater. Sci. Technol. 19 (2003) 785–790.
[10] H. Satoshi, O. Kazutaka, D. Masayuki, O. Hisanori, I. Masahisa, A. Yasuhisa, Q. J. Jpn. Weld. Soc. 21 (2003) 539–545.
[11] W.B. Lee, Y.M. Yeon, S.K. Kim, Y.J. Kim and S.B. Jung In: H.I. Kaplan, Editor, Magnesium Technology 2002, TMS (2002), pp. 309–312.
[12] S. Lim, S. Kim, C.‐G. Lee, C.D. Yim and S.J. Kim, Metall. Mater. Trans. A 36 (2005), pp. 1609–1612.
[13] M. Pareek, A. Polar, F. Rumiche and J.E. Indacochea, Proceedings of the Seventh International Conference on Trends in Welding Research Pine Mountain, GA, United States, May 16–20, 2005, ASM International (2006), pp. 421–426.
[14] W.J. Arbegast, P.J. Hartley, in: Proceedings of the Fifth International Conference of Trends in Welding Research, Pine Mountain, GA, June 1–5, 1998, p. 541.
[15] magnesium‐elektron.com
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