Ti6Al4V alaşımının PTA kaynağında 1800W kaynak gücünde birleştirilebilirliğin araştırılması

Yıl 2015, Cilt: 6 Sayı: 1, 19 - 30, 01.06.2015

Halil Dikbaş Nida Katı

Öz

Bu çalışmada, elektrik enerji endüstrisi, nükleer enerji, petro kimya, otomotiv, uzay araçları ve
medikal endüstrisinde yaygın kullanım alanına sahip Ti ve alaşımlarından Ti6Al4V alaşım çifti
Plazma Transfer Ark (PTA) kaynak yöntemiyle kaynak edilmiştir. Plazma transfer ark kaynağında,
torçla elektrodun etrafından gelen argon gazı tungsten elektrod ve nozul arasındaki pilot ark
sayesinde iyonize olmaktadır. Çalışma esnasında PTA kaynakları, argon koruyucu gaz
atmosferinde, sabit 1800 W kaynak gücünde ve 0,50-0,75-1 m/dk. kaynak hızlarında yapılmıştır.
Kaynak sonrası ITAB’da meydana gelen mikro yapı değişiklikleri optik mikroskop, SEM, EDS ve
XRD analizleri ile incelenmiştir.Malzemenin birleşme mukavemetini belirlemek için çekme deneyi
yapılmıştır. Mikrosertlik ölçümleri Vickers skalasında 50 gr’lık yük altında yapılmıştır. Yapılan
incelemeler sonrasında, mikro ya da makro çatlaklara rastlanmamıştır. Numuneler kaynak dikiş
karakterizasyonu açısından değerlendirildiğinde kot farkı altında oluşan kaynak çukurunun tüm
numunelerde oluşmadığı, ergimiş bölge genişliğinin ve ITAB’ın kaynak hızındaki artışla ters
orantılı olarak arttığı tespit edilmiştir. Mikrosertlik değerlerinin ana metalden ergimiş bölgeye
ilerledikçe arttığı ve en yüksek değere ergimiş bölgede ulaştığı görülmüştür. Ayrıca mikrosertlik
değerlerinin kaynak hızına bağlı olarak ters orantılı arttığı, yüksek kaynak hızında düşük değerde,
düşük kaynak hızında ise yüksek değerde olduğu tespit edilmiştir. Bütün kaynaklarda, kaynak hızı
arttıkça kaynağın mekanik özelliklerinin kötüleştiği tespit edilmiştir. Sabit kaynak gücünde, 0,50
m/dk. kaynak hızıyla yapılan PTA kaynağının, metalurjik açıdan kaynak kalitesi en yüksek
birleştirme olduğu görülmüştür

Anahtar Kelimeler

Ti6Al4V, Plazma Transfer Ark (PTA) Kaynağı, Kaynak Gücü, Kaynak Hızı

The Investigation of the Joinability on 1800W Welding Power on the Plasma Transfer Arc (PTA) Welding of Alloys Ti6Al4V

Öz

In this study; Ti6Al4V alloy couple from the Ti and
its alloys, which are commonly used in electrical
energy industry, nuclear energy, petrochemistry,
automotive, space vehicles and medical industry,
was welded by using Plasma Transferred Arc (PTA)
method. In plasma transferred arc welding; argon
gas coming with the torch from the surrounding of
the electrode is ionized via the pilot arc between the
tungsten electrode and the nozzle. Thus, the plasma
gas that has become conductive passes through the
narrow end of the nozzle and is transferred to the
piece as a narrow column. Shielding gas is
transferred from the external environment of the
nozzle to the weld zone and protects the welding
bath. Cooling liquid coming from the cooling system
goes towards the torch by passing through special
channels and cools the heat here again in the
coolant as a closed circuit. The power source for
plasma welding is almost exclusively DC and, as in
TIG, the drooping, or constant current, output
characteristic will deliver essentially constant
current for a given power source setting. The power
source is ideal for mechanised welding as it
maintains the current setting even when arc length
varies and, in manual welding, it can accommodate
the natural variations of the welder.The plasma
process is normally operated with electrode negative
polarity to minimise heat produced in the electrode
(approximately 1/3rd of the heat generated by the
arc is produced at the cathode with 2/3rds at the
anode). Special torches are available, however, for
operating with electrode positive polarity which rely
on efficient cooling to prevent melting of the
electrode. The positive electrode torch is used for
welding aluminium which requires the cathode to be
on the material to remove the oxide film. AC is not
normally used in the plasma process because it is
difficult to stabilise the AC arc. Problems in
reigniting the arc are associated with constriction by
the nozzle, the long electrode to workpiece distance
and balling of the electrode caused by the alternate
periods of electrode positive polarity. The square
wave AC (inverter, switched DC) power source, with
an efficiently cooled torch, makes the use of the AC
plasma process easier; rapid current switching
promotes arc reignition and by operating with very
short periods of electrode positive polarity,
electrode heating is reduced so a pointed electrode
can be maintained. The plasma system has a unique
arc starting system in which HF is only used to
ignite a pilot arc held within the body of the torch.
Samples were prepared of 80x40x4 mm prior to the
work. During the study, PTA weldings were
performed under argon shielding gas atmosphere at
constant 1800 W welding power and at 0.50-0.75-1
m/min. welding speeds. Microstructure changes,
which occurred in HAZ after the welding, were
examined by optical microscope, SEM, EDS, and
XRD analyses. Samples were prepared by
Metallographic in order to perform this analysis.
Tensile test was applied in order to determine the
joining strength of the material. Tensile tests were
performed ın the drawing device that has 50k/N
load and 1mm/min in tensile speed. Microhardness
measurements were performed under 50-gr load at
Vickers scale. As a result of the examinations
performed, no micro or macro cracks were
observed. Ti6Al4V alloy couple is combined without
a problem by PTA method in Ar atmosphere.
Metallographic terms in the area of the merger is
complete has been found to be void or craters.
When the samples were assessed in terms of weld
nugget characterization; it was found that the
welding cavity occurred under elevation difference
was not observed in all the samples and it increased
as inversely proportional to width of the molten area
width and the increase in the welding speed of HAZ.
According to the XRD analysis results, crystal
systems such as Hexagonal Ti, Cubic Al, Hexagonal
Al2O3, Tetragonal Al3V formed in weldıng seam. It
was observed that microhardness values increased
while progressing from the main metal to the molten
area and reached the maximum value at the molten
area. Furthermore, it was determined that
microhardness values increased as inversely
proportional to the welding speed and they were low
at high welding speed and high at low welding
speed. In all welds, it was observed that as the
welding speed increased, mechanical properties of
the weld deteriorated. It was found that PTA welding
performed at 0.50 m/min. welding speed at constant
welding power was the joining with the highest
welding quality in terms of metallurgical aspect.

Anahtar Kelimeler

Ti6Al4V, Plasma Transfer Arc (PTA) Welding, Welding Power, Welding Speed