Characterization of AA6061-
Galvanized Steel Sheets Joined by
Cold Metal Transfer Welding
Journal Name:
- Dicle Üniversitesi Mühendislik Fakültesi Mühendislik Dergisi
Keywords (Original Language):
Author Name | University of Author | Faculty of Author |
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Abstract (2. Language):
Aluminum alloys are materials providing lightness in
aviation, shipbuilding, railways and automobiles.
Aluminum alloys, which are widely used in
automotive industry, are expensive compared to steel,
also brought about economic concerns. As a result,
hybrid structures made of thin sheet materials, which
aluminum can be used with steel, have been an
economic solution providing lightness. Therefore,
joining of steel with aluminum has become inevitable.
Traditional gas welding methods; Thin parts have not
been successful due to excessive heat input at the
welded joints of different metal alloys such as high
strength aluminum alloys and Fe/Al, which have been
subjected to precipitation hardening. Excessive heat
input causes problems such as deterioration of the
mechanical properties of the weld zone, sensitivity to
hot cracking, pore formation in the weld metal, and
burning and collision, especially in thin sheets.
According to the Fe-Al phase diagram, aluminum
having a low melting point, Fe, Al solid solutions
when contacted with molten steel, and ferric-rich
Fe3Al, FeAl and aluminum rich FeAl2, Fe2Al5, FeAl3
and Fe2Al3 intermetallic compounds, making it
impossible to combine them with conventional gas
welding method.
In recent years, research and development efforts of
welding equipment manufacturers have led to the
emergence of cold metal transfer welding, a new type
of low-energy welding thought to be the solution to
the joining of thin materials and metal alloys with
limited weldability. Cold metal transfer welding
which is characterized with low heat input and
spatter-free weld, is recommended for joining
dissimilar materials. Cold metal transfer welding is a
short-circuiting metal transfer. The droplet
detachment is assisted by a backward movement of
the wire. The wire feeder gives the wire a backdrawing
force when the liquid droplet on the wire tip
contacts the weld pool; meanwhile, the shortingcircuiting
current is reduced to a very low level. Then,
the droplet transfers into the weld pool without liquid
bridge fracture which happens in conventional arc
welding. It indicates that cold metal transfer not only
reduces the heat input but also keeps free of spatters
because it does not need a high current to fracture the
liquid bridge.
In this study, overlap welding of AA6061 and
galvanized steel sheets was carried out by cold metal
transfer method using AlSi5 filler wire. The effect of
heat input on mechanical properties and the
formation of intermetallic compound (IMC) layer
between steel and aluminum were investigated.
Mechanical properties of the joints were determined
by tensile and hardness tests and also applying nano
indentation to intermetallic layer. In order to
determine the elastic modulus and hardness of Al-Fe
intermetallic phases, a nanoindentation test was
applied under a load of 5 mN with Berkovich
indenter. Then nanoindentation test was performed
and P-h curves were obtained. It has been determined
that the intermetallic layer of sample A has higher
mechanical properties than sample B. The EDX
analysis was found to be higher for silicon B than for
sample A. The Al8Fe2Si phase formed in B sample is
proved by the results of nano indentation which
reduces the intermetallic layer's brittleness. It has
been found that the heat input formed during welding
acts on the type and thickness of the intermetallic
formed between Al / Steel.
The hardness of this region is lower than that of
sample A because of grain refinement in the steel
main material of B sample. In both cases, the lowest
hardness values were determined on the weld metal.
When the tensile strength of the welded samples is
examined, the maximum tensile strength and the unit
elongation values are increased by increasing the
heat input (provided that thickness of the
intermetallic is less than 10 μm).
SEM-EDX analysis revealed the formation of FeAl
and Al3Fe in sample A, and Al3Fe and Al8Fe2Si
intermetallics in sample B. The hardness and
modulus of elasticity of the intermetallic layer formed
at A were higher than the B sample.
As a result; by cold metal transfer welding, It can be
successfully combined with Al-Steel sheets by using
appropriate welding parameters and intermetallic
layer thickness control, can prevent the parts from
heating up more adversely affecting the mechanical
properties of the joints compared to other arc welding
methods.
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Abstract (Original Language):
Bu çalışmada, AA6061 ve galvanizli çelik sacların birleştirilmesi, bindirme kaynağı şeklinde AlSi5 dolgu teli
kullanılarak soğuk metal transfer kaynağı ile gerçekleştirilmiştir. Isı girişinin, çelik ve alüminyum arasındaki
intermetalik bileşik tabakasının oluşumu ve bu tabakanın kaynaklı sacların mekanik özelliklerine etkisi
araştırılmıştır.
Bu kaynak yöntemi, Temel olarak düşük akım, düşük voltaj ve düşük ısı girdisi ile karakterize edilir ve
kısa devre (daldırma transferi) modunda çalışmaktadır. Soğuk metal transferi kaynağı ile birleştirilmiş
sacların mekanik özellikleri, çekme ve sertlik testleri ile intermetalik tabakanın ise nano indentasyon testi
uygulanarak belirlenmiştir. Kaynaklı numunelerin çekme dayanımı incelendiğinde ısı girdisinin artmasıyla
maksimum çekme dayanımı ve birim uzama değerleri artmıştır. Kaynak sırasında oluşan ısı girdisinin Al/Çelik
arasında oluşan intermetaliklerin çeşidi ve tabaka kalınlığı üzerinde etkili olduğu bulunmuştur. SEM-EDX
analizleri sonucunda elde edilen miktarlara göre hesaplamalardan ve faz diyagramından A numunesinde FeAl
ve Al3Fe, B numunesinde ise Al3Fe ve Al8Fe2Si intermetaliklerinin oluşumuna rastlanmıştır. A numunesinde
oluşan intermetalik tabakanın sertlik ve elastisite modülü B numunesine göre daha yüksek elde edilmiştir.
Sonuçta; soğuk metal transfer kaynağı diğer ark kaynak yöntemleri ile kıyaslandığında parçaların daha fazla
ısınarak bağlantının mekanik özelliklerini kötü etkilemesi önlenebilecek ve böylece Al-Çelik saclarının uygun
kaynak parametreleri kullanılarak ve intermetalik tabaka kalınlığı kontrollü oluşturularak soğuk metal
transferi kaynağı ile başarılı bir şekilde birleştirilebilecektir.
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