Effect of interfacial reaction layer on the cracking behavior in 3

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					                                          World Journal Of Engineering




          Effect of interfacial reaction layer on the cracking behavior in 3-ply
                                            Mg/Al/STS clad-metal
                                In-Kyu Kim, Jun-Young Song and Sun Ig Hong*
                Department of Advanced Materials Engineering, Chungnam National University, Daejon
                                              *e-mail:sihong@cnu.ac.kr

Introduction                                                        31), Al(Al 3004) and STS(STS430) sheet was 0.3mm,
                                                                    0.55mm and 0.5mm respectively. Al(Al 3004) sheet was
  In recent years, development and application of                   inserted between the Mg(AZ 31) sheet and STS(STS 430)
lightweight materials based on magnesium have been                  sheet to enhance the bonding strength. Table 1 shows the
explored in many developed countries [1–3]. For instance,           chemical composition of the materials used.
research on Mg alloy focusing on mechanical properties                The roll bonded 3-ply Mg/Al/STS metal was heat
has become very active in the lastdecade [4–6]. However,            treated at various temperatures (200, 300, 400℃ for 1hr
Mg and its alloys have crucial drawbacks such as poor               and 400℃ for 3hrs). To examine the interfacial
corrosion resistance, poor formability and high cost,               properties, the tensile test were performed using a
compared to Al and its alloys.Mg/Al clad metal is one               Universal Materials Testing Machine (UNITED,
way to improve the poor corrosion resistance of Mg alloy            US/SSTM). Tensile specimens with a gauge length of
plate. Al alloys have excellent corrosion resistance                15mm and the gauge width of 3.4mm were used. The
because of the formation of thermodynamically stable                cross-head speed was 0.9 mm/min, corresponding to an
Al2O3 protective surface oxide layer and can protect Mg             initial strain rate of 1×10−3/ sec. To examine the variation
against the oxidation and corrosion if they were clad onto          of the hardness across the interface, the Vickers micro-
the Mg alloys. Stainless steel also has many desirable              hardness measurements were made by a Vickers hardness
properties which can be exploited in a wide range of                tester (AKASHI JP/HM-122). Microstructures at the
structural applications. It has corrosion-resistance and            bonding interfaces were observed by an optical
excellent mechanical strength [7]. Despite these attractive         microscope (OM). The chemical compositions were
properties of steels (STS), higher density of stainless             analyzed at the joint interface by an energy dispersive x-
steels limited the application of steels to vehicular               ray analysis (EDX).
applications. Cladding Mg alloys to stainless steels can
reduce the density of material and still exploit the                Results and Discussion
excellent corrosion resistance of stainless steels.
Methods for fabricating clad materials include overlay              Fig.1 shows the optical micrographs ofMg/Al interface
welding, explosion welding, extrusion, and rolling [8,9].           for as-roll-bonded and annealed clad metals. When
Explosion      welding     methods       are     well-known
                                                                    annealing temperature was at and above 300℃, reaction
manufacturing processes for aluminum but this method
                                                                    product between Mg and Al were observed at Mg/Al
entails a high cost and has a number of limitations [10].
                                                                    interfaces.
The roll bonding method is currently the most common
process for producing clad sheets because of its efficiency           Table 1 Chemical compositions of stainless steel(STS 430),
and cost-effectiveness, compared to other processing                 Al(Al 3004) and Mg(AZ 31) used in the present study. (wt. %)
methods.
  In this work, the interfacial reaction during annealing            Comp                         Material Components Properties
                                                                      STS         Fe       Cr      Mn     Si    C      P      S
and its effect on the mechanical properties of the roll-
                                                                    (STS 430)   79.8~84   16~18     1     1    0.12   0.04   0.03
bonded Mg(AZ 31)/aluminum(Al 3004)/18%Cr ferritic
                                                                       Al         Al       Mn      Mg     Fe    Si     Cu     Zn    Other
stainless steel (STS 430) clad metals fabricated by a
                                                                    (Al 3004)   95.5~98   1~1.5     1    0.7    0.3   0.25   0.25   0.15
roll-bonding process were studied. The objective of this
investigation is toexamine the mechanical properties of
annealed cladmetals in relation to the interfacial
properties and to observe the interface structure.

Experimental

 3-ply Mg/Al/STS clad-metal was fabricated by the roll
bonding process. Mg/Al/STS clad-metal used in this
study have a total thickness of 3.8mm and that of Mg(AZ


                                                              561
                                                      World Journal Of Engineering

  Mg        Mg        Al      Zn   Mn    Si    Cu      Ni      Fe     Other

(AZ 31)   93.6~97   2.5~3.5   1    0.5   0.1   0.05   0.005   0.005    0.3             Fig.3 Stress-strain responses of as-roll-bonded clad plates
                                                                                                annealed plates at varioustemperatures.
                                                                                    Conclusion
Fig.1Optical micrographs of Mg/Al interface region in
Mg/Al/STS cladmetals (a) as-roll-bonded Mg/Al interface
(b)~(e) Mg/Al interface annealed at 200℃ for 1hr(b), 300℃ for                       Interfacial compound layer was observed at the Mg/Al
1hr (c), 400℃ for 1hr (d) and 400℃ for 3hr(e)                                       interface after annealing at and above 300℃, which
                                                                                    deteriorated the mechanical strength of clad materials.
Fig.2 (a) shows the reaction compound layer between Al                              However, no visible interfacial reaction compounds were
and Mg and the elemental distribution of Mg and Al                                  observed at Al/STS interfaces even after annealing up to
across the interface. The ratio of Al to Mg peak intensity                          400℃. The thickness of reaction compound layer
is close to Al3Mg2.                                                                 depended on theannealing time and temperature and
                                                                                    increased with annealing time and temperature.The
                                                                                    reactionphase werepresumed to be Al3Mg2. The clad
                                                                                    plates annealed at 200℃ showed a slightly increased
                                                                                    ductility, suggesting the enhanced interfacial bonding.
                                                                                    However, both the critical strain until the first drop of
                                                                                    stress and the total fracture strain decreased with
                                                                                    increasing annealing temperature and time, suggesting the
                                                                                    detrimental effect of annealing at and above 300℃.

                                                                                    Acknowledgements

                                                                                    This work was supported by a grant from the
                                                                                    Fundamental R & D Program for Core Technology for
                                                                                    Materials (2009) funded by the Ministry of Knowledge
                                                                                    Economy.

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