10 A Novel High-Efficiency Keyhole Tungsten Inert Gas …
323
Wang proposed a new method of TIG welding by using double-pulsed variable
polarity with ultrasonic frequency on 7 mm AA2219 aluminium alloy [18]. In the
pulse peak stage of low frequency, the formation of the stable keyhole was achieved.
Besides, the double pulses show a function of stirring the weld pool which resulted in
grain structures with fully equiaxed within the weld zone. A consistent distribution
can be seen in both the microstructure within the welding joint and its microhardness.
10.2.2.6 Material
More extensions of the trials on other materials were studied by various researchers.
8 mm AISI 430 steel plates were successfully welded with different modified of
K-TIG welding, including using high-frequency pulse arc, adding austenite interlayer and imply post-welding heat treatment [19]. It was found that the heat input
decreased, the primary columnar austenite generated.
Keyhole TIG welding was tested in amour grade quenched and tempered (Q&T)
steel, and full penetrated seam was got on 9 mm thick plates, with speed of 28 cm/min
[14]. Huang used K-TIG welding to joint different materials such as AISI 304 stainless steel and Q345 low-alloy steel of 8 mm thickness with just one pass of welding
[20]. The microstructure and welding properties of dissimilar joints were analyzed,
and it is concluded that a good weld seam jointed with different steels can be achieved
with a relatively high welding speed within an operating window of 50 A.
Mid-thickness AISI316L stainless steel was welded by Feng [21]. It was found that
the weld seam consists of different phases including austenite, dendritic structures
and δ-ferrite. The seam and the base metal have a similar strength but the impact
property within the seam was lower.
10.2.3 Application Extensions of K-TIG
10.2.3.1 Pipes Welding
Flat position weldment is the original application of the keyhole TIG welding, but
actually the range of application can be extended including pipes welding. The
keyhole TIG welding has be also used in girth welding of rotated pipes, which can
effectively produce joints of high quality, as shown in Fig. 10.8. It is the preferred
method over other welding technology because it eases the control of the welding
parameter and produces good quality joints. However, some additional constraints
are brought into the pipes welding compared with the flat plate welding.
One problem is the start of weld which will be overlapped at the end of the
process, and defects may be left. In addition, the sudden termination of the K-TIG
welding leads to porosity, underfill and burn-through. Especially, when the current
drops down below the threshold and the pipes keep rotating, porosity is usually seen
in the joints. That is, because the current reduction results in the close of the keyhole,
323
Wang proposed a new method of TIG welding by using double-pulsed variable
polarity with ultrasonic frequency on 7 mm AA2219 aluminium alloy [18]. In the
pulse peak stage of low frequency, the formation of the stable keyhole was achieved.
Besides, the double pulses show a function of stirring the weld pool which resulted in
grain structures with fully equiaxed within the weld zone. A consistent distribution
can be seen in both the microstructure within the welding joint and its microhardness.
10.2.2.6 Material
More extensions of the trials on other materials were studied by various researchers.
8 mm AISI 430 steel plates were successfully welded with different modified of
K-TIG welding, including using high-frequency pulse arc, adding austenite interlayer and imply post-welding heat treatment [19]. It was found that the heat input
decreased, the primary columnar austenite generated.
Keyhole TIG welding was tested in amour grade quenched and tempered (Q&T)
steel, and full penetrated seam was got on 9 mm thick plates, with speed of 28 cm/min
[14]. Huang used K-TIG welding to joint different materials such as AISI 304 stainless steel and Q345 low-alloy steel of 8 mm thickness with just one pass of welding
[20]. The microstructure and welding properties of dissimilar joints were analyzed,
and it is concluded that a good weld seam jointed with different steels can be achieved
with a relatively high welding speed within an operating window of 50 A.
Mid-thickness AISI316L stainless steel was welded by Feng [21]. It was found that
the weld seam consists of different phases including austenite, dendritic structures
and δ-ferrite. The seam and the base metal have a similar strength but the impact
property within the seam was lower.
10.2.3 Application Extensions of K-TIG
10.2.3.1 Pipes Welding
Flat position weldment is the original application of the keyhole TIG welding, but
actually the range of application can be extended including pipes welding. The
keyhole TIG welding has be also used in girth welding of rotated pipes, which can
effectively produce joints of high quality, as shown in Fig. 10.8. It is the preferred
method over other welding technology because it eases the control of the welding
parameter and produces good quality joints. However, some additional constraints
are brought into the pipes welding compared with the flat plate welding.
One problem is the start of weld which will be overlapped at the end of the
process, and defects may be left. In addition, the sudden termination of the K-TIG
welding leads to porosity, underfill and burn-through. Especially, when the current
drops down below the threshold and the pipes keep rotating, porosity is usually seen
in the joints. That is, because the current reduction results in the close of the keyhole,