8
S. K. Das et al.
same time has longer life. Different materials employed for making FSW tools as
well as effective tool geometry tool geometry are discussed in the following texts:
1.4.1 Materials for FSW Tool
Tool materials for FSW of high-temperature alloys should have excellent mechanical properties so that it can perform successfully at higher operating temperatures
(above 900 °C). The properties include ductility, hardness, thermal conductivity and
coefficient of thermal expansion. The selection of the tool materials depends on the
recrystallization temperatures of the work piece. Tool materials are required to have
necessary strength to survive the process temperature as well have fatigue strength
and fracture toughness at the same temperature conditions [37]. Besides, the tool
also needs to have good wear characteristics and thermal and chemical stability
(inert toward the workpiece material). Apart from this, tool wear and its life are
also important factors behind the selection of tool material. And the final deciding
factor remains the quality of weld produced by the tool. Steel is the popular choice
as tool material for welding of aluminum and magnesium alloys. Polycrystalline
cubic boron nitride (PCBN) and W-based tools on the other hand have been used for
welding of hard material such as steel and titanium.
1.4.1.1 Tool Material for Low-Temperature Alloys
It is easy to find suitable tool material for processing aluminum alloys as aluminum
is softer and has a lower melting point than many of the other metals. For FSW
of aluminum alloys, the tool material requires to sustain the process conditions.
Besides, it should also possess properties, viz. fracture toughness, long fatigue life,
wear resistance, chemical stability and thermal stability. Tool steel (H13 tool steel)
and cobalt-based super-alloy (MP159) are among the common tool materials used
for FSW of aluminum and its alloys [37, 52]. Prado et al. [50] employed tool steel
for FSW of aluminum MMC (aluminum alloys 6061+20%Al 2 O 3 ). They found that
the tool was quite effective and suffered minimum wear in case of welding Al 6061
compared to when Al 2 O 3 particles were added (refer Fig. 1.4. They further found
that the tool suffered maximum wear when operated at 1000 rpm post which the wear
decreases but in an irregular manner (see Fig. 1.5. Enhancement in the fluidity of the
material and the turbulence in the particle flow beyond 1000 rpm may be the reason
for this decrement. FSW for dissimilar metals has also been carried out successfully
by various researchers. Chen and Lin [7] have carried out a design of experiment for
optimization of the FSW process parameters when welding SS400 low-carbon steel
and AA6061 aluminum alloy using AISI 4140 tool steel. Lee et al. [27] successfully
achieved a lap joint between Al–Mg alloy and low-carbon steel using tool made of
tool steel. They carried out the welding joint without excessive tool wear by putting
the Al–Mg alloy plate above the steel plate. In this way, the tool made direct contact
S. K. Das et al.
same time has longer life. Different materials employed for making FSW tools as
well as effective tool geometry tool geometry are discussed in the following texts:
1.4.1 Materials for FSW Tool
Tool materials for FSW of high-temperature alloys should have excellent mechanical properties so that it can perform successfully at higher operating temperatures
(above 900 °C). The properties include ductility, hardness, thermal conductivity and
coefficient of thermal expansion. The selection of the tool materials depends on the
recrystallization temperatures of the work piece. Tool materials are required to have
necessary strength to survive the process temperature as well have fatigue strength
and fracture toughness at the same temperature conditions [37]. Besides, the tool
also needs to have good wear characteristics and thermal and chemical stability
(inert toward the workpiece material). Apart from this, tool wear and its life are
also important factors behind the selection of tool material. And the final deciding
factor remains the quality of weld produced by the tool. Steel is the popular choice
as tool material for welding of aluminum and magnesium alloys. Polycrystalline
cubic boron nitride (PCBN) and W-based tools on the other hand have been used for
welding of hard material such as steel and titanium.
1.4.1.1 Tool Material for Low-Temperature Alloys
It is easy to find suitable tool material for processing aluminum alloys as aluminum
is softer and has a lower melting point than many of the other metals. For FSW
of aluminum alloys, the tool material requires to sustain the process conditions.
Besides, it should also possess properties, viz. fracture toughness, long fatigue life,
wear resistance, chemical stability and thermal stability. Tool steel (H13 tool steel)
and cobalt-based super-alloy (MP159) are among the common tool materials used
for FSW of aluminum and its alloys [37, 52]. Prado et al. [50] employed tool steel
for FSW of aluminum MMC (aluminum alloys 6061+20%Al 2 O 3 ). They found that
the tool was quite effective and suffered minimum wear in case of welding Al 6061
compared to when Al 2 O 3 particles were added (refer Fig. 1.4. They further found
that the tool suffered maximum wear when operated at 1000 rpm post which the wear
decreases but in an irregular manner (see Fig. 1.5. Enhancement in the fluidity of the
material and the turbulence in the particle flow beyond 1000 rpm may be the reason
for this decrement. FSW for dissimilar metals has also been carried out successfully
by various researchers. Chen and Lin [7] have carried out a design of experiment for
optimization of the FSW process parameters when welding SS400 low-carbon steel
and AA6061 aluminum alloy using AISI 4140 tool steel. Lee et al. [27] successfully
achieved a lap joint between Al–Mg alloy and low-carbon steel using tool made of
tool steel. They carried out the welding joint without excessive tool wear by putting
the Al–Mg alloy plate above the steel plate. In this way, the tool made direct contact