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J. M. Sánchez-Amaya and C. Churiaque
9.1 Introduction
As in other metal alloys, the weldability of titanium alloys depends, among other
properties, on their chemical composition [1]. Titanium alloys are conventionally
classified into three categories, according to their microstructure: α alloys (consisting
of various grades of commercially pure titanium alloys), α + β alloys (presenting
α phase and a small volume fraction of β phase in equilibrium, although martensite
transformation can also occur upon fast cooling) and β alloys (which do not transform
martensitically upon fast cooling from the β phase field) [2]. The weldability of titanium alloys is known to be strongly influenced by the category previously described.
Thus, it is reported in [3] that unalloyed titanium and all α titanium alloys have
good weldability, toughness and strength. α + β alloys show good formability and
weldability, their properties being highly influenced by heat treatments. β alloys are
claimed to present worse weldability due to the degradation of strength after welding
[4]. Ahmed et al. also reported in [1] that pure titanium, α alloys and α + β alloys have
excellent weldability, although metastable β alloys have limited weldability due to
the high content of β stabilizing elements. These general weldability considerations
are applied regardless of the joining technology, but specific welding techniques can
modulate this ability. Therefore, it is possible to improve the weldability employing
novel joining processes.
Among the different novel welding technologies, laser beam welding (LBW)
presents different advantages and is specially suitable to join titanium alloys, as it
allows a high localization and low size of the melting pool, the required energy being
considerably reduced. Many research papers have demonstrated the applicability
of LBW to join different titanium alloys, especially for automotive and aerospace
industries [5, 6]. Some examples of these studies, developed by the authors of the
present contribution, focusses on different aspect of the process when LBW is applied
under conduction regime, as the analyses of LBW heat source shape in Ti 6 Al 4 V alloy
by FEM simulation [7], the influence of surface pre-treatments in LBW of Ti 6 Al 4 V
alloy [8], the analysis of microstructure and properties of laser welded Ti5553 (β
alloy) samples [9], or the corrosion [10] and tribocorrosion [11] behaviour of laser
treated CPTi and Ti 6 Al 4 V samples.
As stated before, the weldability of some titanium alloys is rather bad, although
innovative welding technologies, as LBW, can be employed to improve it. The objective of this communication is to determine experimentally and precisely the range of
laser weldability of the most common three families of titanium alloys. To carry out
this study, full penetration butt welds were prepared using LBW under conduction
regime, in specimens of different titanium alloys with the same thickness and size.
Specifically, samples of an α (CpTi) alloy, an α + β alloy (Ti 6 Al 4 V) and a β alloy
(Ti 5 Al 5 V5Mo 3 Cr) have been studied. This selection allowed the authors study the
laser weldability of representative titanium alloys families existing in the market.
J. M. Sánchez-Amaya and C. Churiaque
9.1 Introduction
As in other metal alloys, the weldability of titanium alloys depends, among other
properties, on their chemical composition [1]. Titanium alloys are conventionally
classified into three categories, according to their microstructure: α alloys (consisting
of various grades of commercially pure titanium alloys), α + β alloys (presenting
α phase and a small volume fraction of β phase in equilibrium, although martensite
transformation can also occur upon fast cooling) and β alloys (which do not transform
martensitically upon fast cooling from the β phase field) [2]. The weldability of titanium alloys is known to be strongly influenced by the category previously described.
Thus, it is reported in [3] that unalloyed titanium and all α titanium alloys have
good weldability, toughness and strength. α + β alloys show good formability and
weldability, their properties being highly influenced by heat treatments. β alloys are
claimed to present worse weldability due to the degradation of strength after welding
[4]. Ahmed et al. also reported in [1] that pure titanium, α alloys and α + β alloys have
excellent weldability, although metastable β alloys have limited weldability due to
the high content of β stabilizing elements. These general weldability considerations
are applied regardless of the joining technology, but specific welding techniques can
modulate this ability. Therefore, it is possible to improve the weldability employing
novel joining processes.
Among the different novel welding technologies, laser beam welding (LBW)
presents different advantages and is specially suitable to join titanium alloys, as it
allows a high localization and low size of the melting pool, the required energy being
considerably reduced. Many research papers have demonstrated the applicability
of LBW to join different titanium alloys, especially for automotive and aerospace
industries [5, 6]. Some examples of these studies, developed by the authors of the
present contribution, focusses on different aspect of the process when LBW is applied
under conduction regime, as the analyses of LBW heat source shape in Ti 6 Al 4 V alloy
by FEM simulation [7], the influence of surface pre-treatments in LBW of Ti 6 Al 4 V
alloy [8], the analysis of microstructure and properties of laser welded Ti5553 (β
alloy) samples [9], or the corrosion [10] and tribocorrosion [11] behaviour of laser
treated CPTi and Ti 6 Al 4 V samples.
As stated before, the weldability of some titanium alloys is rather bad, although
innovative welding technologies, as LBW, can be employed to improve it. The objective of this communication is to determine experimentally and precisely the range of
laser weldability of the most common three families of titanium alloys. To carry out
this study, full penetration butt welds were prepared using LBW under conduction
regime, in specimens of different titanium alloys with the same thickness and size.
Specifically, samples of an α (CpTi) alloy, an α + β alloy (Ti 6 Al 4 V) and a β alloy
(Ti 5 Al 5 V5Mo 3 Cr) have been studied. This selection allowed the authors study the
laser weldability of representative titanium alloys families existing in the market.