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Remanufacturing and Advanced Machining
applied both to pure metals including hard-to-deform ones, such as tungsten or titanium, and to alloys. In the case of difficult-to-deform metals and alloys, the ECAP
process is performed at elevated temperatures. It should be noted that the conditions
such as time and temperature of the subsequent passages may be varied.
There are also several modified ECAP methods, listed below (Segal, 2018):
• Continuous ECAE-conform method for processing of long materials
• Semi-continuous incremental-ECAP method, where material shearing and
feeding are separated for small successive steps to reduce press capacity,
making processing of long billets possible
• Multi-pass ECAE in rotary dies or at special presses, without billet ejection
after each pass
• Tubular-channel angular pressing consisting of a three-step passage of a
pipe sample through channels formed between a die and mandrel, which
can only be applied to relatively short tubes
Superplastic forming of NC materials at low homologous temperatures or high strain
rates has been among the first examples of applying NC materials forming as a nearnet-shape production process. It is a favorable shape-forming method, since complex
shapes can be obtained without involving multistep processing routes and thus in a
cost-effective manner (Wilde, 2014).
Friction stir processing (FSP), an adaptation of the solid-state joining process
friction stir welding (FSW) described in Section 1.13.2, also belongs among widely
recognized SPD techniques. Friction stir processing with three consecutive passes
causes a dramatic decrease in the grain size from 23 ± 2 μm of the base material of
Mg–Y–Nd alloy to 2.1 ± 1 μm, about 90% of the grains are converted to an ultrafine
grain microstructure below 1 μm after the second FSP pass in 6-mm thick magnesium silver earth (QE22) specimens, while 80% of the grains are changed to ultrafine
structure after the first pass, and for AZ31 Mg alloy two-pass FSP (1,000 rpm with a
travel speed of 37 mm/min for both the passes) results in nano-grains of average size
85 nm (Harwani et al., 2021).
Unlike FSW, where samples are joined, FSPutilizes the same process principles
to modify the local microstructure of monolithic specimens (Węglowski, 2018). As
can be seen in Figure 3.7, a rotating tool travels along a workpiece to achieve specific
and desired properties by surface modification, since frictional heat and mechanical
stirring lead to grain refinement in the FSP region where the tool has passed.
Like in FSW, the tool induces a plastic flow during the friction stir process, but
depending on the selection of process parameters, i.e., applied force, traveling speed,
and rotational speed, the material flow can yield a modified microstructure that is
beneficial to the required performance of the material (Węglowski, 2018). The width
of the processed zone after a single pass of the tool is slightly wider than the diameter of a pin.
The grain size reduction is achieved by increasing tool rotation speed and a simultaneous decrease in the tool traverse speed v. Higher tool rotation accounts for a
faster breakup of grains combined with greater mechanical intermixing of particles,
Remanufacturing and Advanced Machining
applied both to pure metals including hard-to-deform ones, such as tungsten or titanium, and to alloys. In the case of difficult-to-deform metals and alloys, the ECAP
process is performed at elevated temperatures. It should be noted that the conditions
such as time and temperature of the subsequent passages may be varied.
There are also several modified ECAP methods, listed below (Segal, 2018):
• Continuous ECAE-conform method for processing of long materials
• Semi-continuous incremental-ECAP method, where material shearing and
feeding are separated for small successive steps to reduce press capacity,
making processing of long billets possible
• Multi-pass ECAE in rotary dies or at special presses, without billet ejection
after each pass
• Tubular-channel angular pressing consisting of a three-step passage of a
pipe sample through channels formed between a die and mandrel, which
can only be applied to relatively short tubes
Superplastic forming of NC materials at low homologous temperatures or high strain
rates has been among the first examples of applying NC materials forming as a nearnet-shape production process. It is a favorable shape-forming method, since complex
shapes can be obtained without involving multistep processing routes and thus in a
cost-effective manner (Wilde, 2014).
Friction stir processing (FSP), an adaptation of the solid-state joining process
friction stir welding (FSW) described in Section 1.13.2, also belongs among widely
recognized SPD techniques. Friction stir processing with three consecutive passes
causes a dramatic decrease in the grain size from 23 ± 2 μm of the base material of
Mg–Y–Nd alloy to 2.1 ± 1 μm, about 90% of the grains are converted to an ultrafine
grain microstructure below 1 μm after the second FSP pass in 6-mm thick magnesium silver earth (QE22) specimens, while 80% of the grains are changed to ultrafine
structure after the first pass, and for AZ31 Mg alloy two-pass FSP (1,000 rpm with a
travel speed of 37 mm/min for both the passes) results in nano-grains of average size
85 nm (Harwani et al., 2021).
Unlike FSW, where samples are joined, FSPutilizes the same process principles
to modify the local microstructure of monolithic specimens (Węglowski, 2018). As
can be seen in Figure 3.7, a rotating tool travels along a workpiece to achieve specific
and desired properties by surface modification, since frictional heat and mechanical
stirring lead to grain refinement in the FSP region where the tool has passed.
Like in FSW, the tool induces a plastic flow during the friction stir process, but
depending on the selection of process parameters, i.e., applied force, traveling speed,
and rotational speed, the material flow can yield a modified microstructure that is
beneficial to the required performance of the material (Węglowski, 2018). The width
of the processed zone after a single pass of the tool is slightly wider than the diameter of a pin.
The grain size reduction is achieved by increasing tool rotation speed and a simultaneous decrease in the tool traverse speed v. Higher tool rotation accounts for a
faster breakup of grains combined with greater mechanical intermixing of particles,