materials

Article
The Effect of Novel Complex Treatment of Annealing and
Sandblasting on the Microstructure and Performance of Welded
TA1 Titanium Plate
Yanbin Xu 1,2 , Dayue Wang 3 , Mingyen Li 3 , Jing Hu 1,2, * , Xulong An 1,2 and Wei Wei 1,2

1 Jiangsu Key Laboratory of Materials Surface Science and Technology, Huaide College, Changzhou University,
Changzhou 213164, China
2 National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University,
Changzhou 213164, China
3 Changzhou Sinosteel Precision Forging Materials Co., Ltd., Changzhou 213150, China
* Correspondence: jinghoo@126.com

Abstract: The welding titanium cathode roller has the obvious advantages of low cost, high efficiency,
and no diameter restriction. Unfortunately, the longitudinal weld on the cathode roller adversely
impacts the quality of the electrolytic copper foil due to the great difference between the microstruc-
ture of the weld zone and the base metal. Thus, it is crucial to reduce their difference by regulating
the microstructure of the weld zone. In this study, a novel complex treatment of heat treatment
and sandblasting is primarily developed for regulating the microstructure of the weld zone. The
results show that the novel complex treatment has an efficient effect on regulating the microstructure
of the weld zone and making the microstructure in the weld zone close to that of the base metal.
During vacuum annealing, the microstructure of the weld zone is refined to some degree, and 650 ◦ C
annealing has the optimal effect, which can effectively reduce the ratio of α phase’s length to width
and reduce the microstructure difference between the weld zone and the base metal. At the same
time, with an increase in the annealing temperature, the tensile strength and yield strength decreased
by about 10 MPa; the elongation after fracture increased by 20%; the average microhardness of the
WZ and the HAZ decreased by about 10 HV0.10 ; and that of the BM decreased by about 3 HV0.10 .
Citation: Xu, Y.; Wang, D.; Li, M.; Hu, The heat treatment after welding can effectively adjust the properties of the weld zone, reduce the
J.; An, X.; Wei, W. The Effect of Novel hardness and strength, and improve the toughness. The subsequent sandblasting after annealing can
Complex Treatment of Annealing and further refine the grain size in the weld zone and make the microstructure in the weld zone close to
Sandblasting on the Microstructure that of the base metal. Sandblasting after annealing can further refine the grain in the weld zone and
and Performance of Welded TA1
make the microstructure in the weld zone close to that of base metal. Meanwhile, an application test
Titanium Plate. Materials 2023, 16,
confirmed that the adverse impact of a longitudinal weld on the quality of electrolytic copper foil
2149. https://doi.org/10.3390/
could be resolved by adopting this novel complex treatment. Therefore, this study provides valuable
ma16062149
technical support for the “welding” manufacturing of the titanium sleeves of the cathode roller.
Academic Editor: Shinichi Tashiro

Received: 2 January 2023

Keywords: TA1 titanium plate; weld; heat treatment; electrolytic copper foil; cathode roller
Revised: 2 March 2023
Accepted: 6 March 2023
Published: 7 March 2023
1. Introduction
Electrolytic copper foil is one of the important materials for manufacturing copper-clad
laminate (CCL) and printed circuit boards (PCB) [1,2]. In recent years, due to the rapid
Copyright: © 2023 by the authors.
development of science and technology in the downstream industry, higher requirements
Licensee MDPI, Basel, Switzerland.
have been put forward for the upstream electrolytic copper foil. Not only is its demand
This article is an open access article
distributed under the terms and
increasing, but the quality requirements for copper foil are also getting higher. At present,
conditions of the Creative Commons
there are two kinds of methods for producing copper foil, one is calendering, and the
Attribution (CC BY) license (https://
other is electrolysis [3,4]. Electrolytic production of copper foil is an efficient production
creativecommons.org/licenses/by/ method developed in recent years [5–7]. This technology has two major advantages,
4.0/). high efficiency and low cost [8]. It uses a roller cathode that rotates slowly at a constant

Materials 2023, 16, 2149. https://doi.org/10.3390/ma16062149 https://www.mdpi.com/journal/materials

Materials 2023, 16, 2149 2 of 10

speed to continuously produce a certain width of electrolytic copper foil. With the rapid
development of China’s electrolytic copper foil industry, the demand for cathode rollers
and the key equipment for producing copper foil is also increasing significantly yearly. As
a core and key component of electrolytic copper foil equipment, the quality of the cathode
roller determines the grade and quality of the copper foil.
There are two methods for manufacturing the titanium sleeve used for the cathode
roller, “spinning” and “welding” [9]. The cathode roller manufactured by “welding” has
many advantages, such as low production cost, high production efficiency, and it can
meet flexible diameter requirements. Unfortunately, “welding” manufacturing has an
unacceptable shortcoming, a longitudinal weld on the surface of the cathode roller, which
forms a “bright” band on the copper foil surface in the corresponding position of the
longitudinal weld and thus seriously affects the quality of the copper foil and reduces its
production efficiency. Therefore, the key technology of “welding” manufacturing for a
cathode roller is to develop an appropriate technical method to adjust the microstructure of
the weld zone and make it close to the base metal.
It is reported that annealing treatment could refine the grain in the weld zone, but an
obvious difference from the base metal still exists [10]. Therefore, it is necessary to develop
a novel method to further refine the grain size in the weld zone and reduce the difference
between the weld zone and base metal.
In this study, a novel complex treatment of annealing and sandblasting was primarily
used to regulate the microstructure of the weld zone. The research goal is to effectively
refine the grain in the weld zone and make the microstructure close to that of the base metal.

2. Materials and Methods

To avoid the side effect of impurity elements, a fine-grained TA1 titanium plate with
high purity and little oxygen developed by Sinosteel Precision Forging Materials Co., Ltd.
was used as the raw material in this study. Its composition is shown in Table 1, and the
purity of the titanium plate is very high. The titanium plate was welded by manual tungsten
argon arc welding, with a welding current of 120 A and a welding voltage of 23 V. To avoid
the pollution of oxygen and impurity elements in the welding wire to the weld seam,
the direct welding method was adopted. The welding parameters are shown in Table 2.
The welding schematic diagram and physical photograph are shown in Figure 1. The
appearance of the weld seam is shown in Figure 2. It can be seen that the weld seam surface
is relatively flat and smooth. After welding, the welding plate was vacuum annealed at
a temperature range of 500 ◦ C, 550 ◦ C, 600 ◦ C, and 650 ◦ C for 2 h. Then, sandblasting
was conducted at a pressure of 0.6 MPa with a duration of 25 min by a BA600D standard
closed sandblasting machine. The DMI-3000M optical microscope was used to observe the
microstructure, and the corrosion solution was a mixture solution of HF, HNO3, and H2 O,
with a ratio of HF: HNO3 : H2 O = 2:1:40. The mechanical performance of the TA1 titanium
plate at different stages was tested using the American Instron 8802 electro-hydraulic
servo mechanical testing machine. The microhardness of different areas of the sample was
evaluated by the HXD-1000TMC Vickers microhardness tester. Finally, an application test
was conducted by preparing an electrolytic copper foil using a welded titanium plate, and
the surface morphology of the electrolytic copper foil was visually observed.

Table 1. Chemical composition of TA1 titanium plate (wt. %).

Elements C H N O Fe Ti
Content 0.007 0.0006 0.0015 0.032 0.029 Balance
Materials 2023, 16, 2149 3 of 10

Table 2. Welding parameters of manual tungsten pole argon arc welding.

Welding Welding Welding Welding Main Support

Parameters Current/A Voltage/V Speed/(cm·s−1 ) Nozzle/(L·min−1 ) Cover/(L·min−1 )
120 23 0.5 20 12

Figure 1. The welding schematic diagram and physical photograph. (a) Schematic diagram; (b) Phys-
ical photograph.

Figure 2. Appearance of the weld seam.

3. Results and Discussion

3.1. Welded Microstructure of Titanium Plate
After the titanium plate was welded, the microstructure of the weld zone was observed
and compared with that of the base metal (BM), as shown in Figure 3. It can be seen that the
microstructure of the weld zone (WZ) and the base metal (BM) is greatly different. The WZ
is a typical welding microstructure, mainly composed of coarsened columnar β phase along
with a little acicular α phase. There are many irregular cross-flake and acicular structures
due to the effect of heat input, with a much coarser grain size than the BM [11–13], while
the microstructure in the BM is fully composed of an equiaxed α phase.

Figure 3. Microstructure comparison of the weld zone (WZ) and the base metal (BM). (a) Weld zone
(WZ); (b) Base metal (BM).

3.2. Annealed Microstructure of Titanium Plate

The welded plate was vacuum annealed at 500 ◦ C, 550 ◦ C, 600 ◦ C, and 650 ◦ C for 2 h,
and the microstructures in the WZ after annealing at different temperatures are shown
Materials 2023, 16, 2149 4 of 10

in Figure 4. It can be seen that with the increase of annealing temperature, the acicular α
phase in the WZ changes in shape; that is, it changes from an acicular to a lamellar shape,
so it gradually becomes similar to that of the BM. In high-temperature slow cooling, the
coarse β phase in the WZ turns into a fine α phase. Therefore, the structure of the WZ is
composed of α phase and a little α + β two-phase mixture, which is nearer to the structure
of the BM.

Figure 4. Microstructure of the weld zone (WZ) annealed at different temperatures. (a) 500 ◦ C;
(b) 550 ◦ C; (c) 600 ◦ C; (d) 650 ◦ C.

3.3. Mechanical Performance and Microhardness of Annealed Titanium Plate

The mechanical performances of the TA1 titanium plate corresponding to each stage
after annealing are shown in Table 3. It can be seen from the table that the tensile strength
and yield strength of titanium plate substrate are 259 MPa and 152.5 MPa, respectively, and
the elongation after fracture is 66.6%. After welding, the tensile strength and yield strength
increased to 279 MPa and 183 MPa, and the elongation after fracture decreased to 20%. This
may be because the titanium plate contains a small amount of impurity elements, so, during
welding, these impurity elements and welds absorb oxygen and nitrogen from the air to
form an interstitial solid solution, which causes a lattice distortion of the titanium, thus
improving the tensile strength and yield strength, and reducing the elongation after fracture.
In addition, a lot of heat is generated during welding. Thus, the surface temperature of the
titanium plate increases rapidly, resulting in grain growth, and the strength of the titanium
plate increases.

Table 3. Mechanical performance of TA1 titanium plate corresponding to each stage.

Performance Tensile Strength/MPa Yield Strength / MPa Elongation after Fracture/%

Base material 259 152.5 66.6
welding 279 183 20
500 277 180 35
Annealing 550 276 179 38
temperature/◦ C 600 275 175 40
650 270 171 40
Materials 2023, 16, 2149 5 of 10

After the titanium plate was welded and vacuum annealed, the tensile strength
decreased from 279 MPa to 270 MPa with increased annealing temperatures. The yield
strength decreased from 183 MPa to 171 MPa. The elongation after fracture increased
from 20% to 40%. With an increase in annealing temperature, the tensile strength and
yield strength decreased by about 10 MPa, and the elongation after fracture increased
by 20%. This is because annealing causes the recrystallization of the welded titanium
plate, the grain is refined to a certain extent, and the internal stress of the titanium plate
is eliminated, thus reducing the tensile strength and yield strength, and improving the
elongation after fracture.
In general, annealing heat treatment helps reduce the strength after welding and
improves the elongation after fracture.
Figure 5 shows the effect of annealing temperature on the microhardness of different
areas of the welded plate. It can be seen from the figure that the highest hardness of the
titanium plate after welding appears in the WZ, followed by the HAZ, and the lowest
hardness is located in the BM. The highest hardness value appears at 2 mm from the weld
seam center, about 203 HV0.10 . The general trend is a gradual decrease from the WZ to
the BM. This is because during the welding of pure titanium, due to the large amount
of heat generated, the temperature at the weld seam increases rapidly, so the α phase in
the WZ turns into the β phase. In the process of cooling and solidification after welding,
the β phase again turns into the α phase. Still, due to the relatively fast solidification
rate, only a small part of the β phase has changed. Most of the coarse β phase has been
retained. Finally, the weld zone structure is a typical welding structure, mainly composed
of a coarsened columnar β phase along with a little acicular α phase. At the same time,
there are many irregular cross-flake and acicular structures due to the effect of heat input.
Different structures in the WZ produce phase transformation strengthening, so the hardness
of the WZ is on the high side. In addition, because titanium plate contains a small amount
of impurity elements, during welding, these impurity elements and welds absorb oxygen
and nitrogen in the air to form an interstitial solid solution, which causes lattice distortion
of titanium and also increases the hardness of the WZ. The reason the highest hardness
does not appear at the center of the weld seam may be because the high temperature at
the center of the weld seam stays long, and some grains grow, so the hardness decreases
slightly. The microstructure of the BM is completely equiaxed α phase composition, and
the structure of the HAZ is affected by both the WZ and the BM. Therefore, the hardness of
the HAZ takes second place, and the hardness of the BM is the lowest.

Figure 5. Effect of annealing temperature on microhardness of each area of welding plate.

After the titanium plate is welded and then subjected to the vacuum annealing treat-
ment, the average microhardness of the WZ and the HAZ decreases by about 10 HV0.10 ,
and that of the BM decreases by about 3 HV0.10 . In general, with the increase of annealing
temperature, the microhardness of each weld zone is reduced to a certain extent. This
is because annealing causes the recovery and recrystallization of the titanium plate after
welding, which makes the β phase in the HAZ and the WZ turn into the α phase again. It
Materials 2023, 16, 2149 6 of 10

eliminates the phase transformation strengthening caused by different structures, so the

microhardness of each weld area has also been reduced to a certain extent.
In general, the peak hardness of the WZ and the HAZ decreases with the increase in
annealing temperature.

3.4. Sandblasting Microstructure of Titanium Plate

Sandblasting is carried out after vacuum annealing, and the microstructure in the
WZ before and after sandblasting is shown in Figure 6. It can be seen that the annealed
microstructure of the WZ has been refined by the following sandblasting. Especially, the
650 ◦ C annealed-sandblasted microstructure is much finer, with a grain size level close to
that of the BM.

Figure 6. Microstructure comparison of the weld zone (WZ) before and after sandblasting annealed
at different temperatures. (a) 500 ◦ C; (b) 500 ◦ C+ sand blasting; (c) 550 ◦ C; (d) 550 ◦ C + sand blasting;
(e) 600 ◦ C; (f) 600 ◦ C+ sand blasting; (g) 650 ◦ C; (h) 650 ◦ C + sand blasting.
Materials 2023, 16, 2149 7 of 10

The reason is that sandblasting provides high strain conditions for the surface layer,
resulting in many dislocations on the surface layer [14–17]. High-density dislocations also
gradually evolute into dislocation walls, i.e., sub-grain boundaries. As the strain increases,
new dislocations are continuously generated, which evolve into new sub-grain boundaries.
At the same time, the initially formed sub-grain boundaries can be evolved into grain
boundaries so that the grains are refined. Therefore, the microstructure of the WZ can be
further refined after sandblasting, thus reducing the difference between the microstructure
of the WZ and the BM.

3.5. Microhardness of Each Area after Sand Blasting

After vacuum annealing, the welded plate was sandblasted. The microhardness of the
corresponding weld zone under each process condition is shown in Figure 7. It can be seen
that the hardness of the base material increased from about 160 HV0.10 to about 205 HV0.10
after the vacuum annealing and sandblasting of the welded plate. The maximum hardness
affected by heat increased from about 180 HV0.10 to about 226 HV0.10 . The maximum
hardness of the weld zone increased from about 200 HV0.10 to about 250 HV0.10 . In general,
the microhardness of each weld area improved to a certain extent, about 45 HV0.10 , showing
that surface sandblasting effectively improves surface hardness [18–20]. This is because
sandblasting provides high strain conditions for the surface layer of the titanium plate,
resulting in a large number of dislocations on the surface layer. The dislocation density
increases with the increase of deformation, and the high-density dislocation gradually forms
the dislocation wall, namely the subgrain boundary; as the strain continues to increase, new
dislocations are continuously generated, thus improving the microhardness of each area of
the weld. This shows that surface sandblasting effectively improves surface hardness.

Figure 7. Microhardness of each area after sandblasting.

3.6. Grain Size Grade of Weld Zone under Different Processes

The grain size scale is called grain size, usually expressed by the number of grains per
unit volume (or unit area) or the average line length (or diameter) of grains. In industrial
production, grain size grade is used to express grain size. The standard grain size is divided
into 12 grades. Grades 1–4 are coarse grains, grades 5–8 are fine grains, and grades 9–12 are
ultra-fine grains. In this paper, the grain size grade was determined by calculating the
number of grains in a given region. The grain size grade of the WZ under different processes
is shown in Table 4. It can be seen that the grain size grade of the BM is about 9, while the
grain size grade of the WZ after welding is about 5. After vacuum annealing treatment of
the welded titanium plate, the grain size grade of the weld zone after annealing at 500 ◦ C
is raised to about 6. With the annealing temperature rising from 500 ◦ C to 650 ◦ C, the
Materials 2023, 16, 2149 8 of 10

grain size grade of the weld zone is raised from about 6 to about 7. This shows that the
grain size grade of the weld zone can be effectively improved by the heat treatment of the
welding retrogression. This is because annealing causes the recovery and recrystallization
of the welded titanium plate, and the grain size is refined to a certain extent, so the grain
size grade of the WZ is continuously improved with an increase in annealing temperature.
After vacuum annealing treatment and sandblasting treatment, the grain size grade of the
WZ was raised from 7 to about 8. The grain size of the WZ is about 9, only 1 grade different
from the grain size after annealing + sandblasting, indicating that sandblasting can further
improve the grain size grade of the WZ. This is because sandblasting provides high strain
conditions for the surface layer, resulting in a large number of dislocations on the surface
layer, refining the grains. This shows that the annealing + sandblasting can better refine the
grain size, improve its microstructure, and reduce the difference between the WZ and the
BM structure.

Table 4. Grain size grade of the WZ under different processes.

Process Original 500 ◦ C + 550 ◦ C + 600 ◦ C + 650 ◦ C +

500 ◦ C 550 ◦ C 600 ◦ C 650 ◦ C
Parameters Sample Sandblasting Sandblasting Sandblasting Sandblasting
grain size
9 6 6.5 6.5 7 6.5 7 7.5 8
grade

3.7. Morphology Comparison of the Electrolytic Copper Foil

To confirm whether the adverse impact of longitudinal weld on the quality of elec-
trolytic copper foil can be resolved by this novel complex treatment, an application test
was conducted by preparing an electrolytic copper foil using a welded titanium plate with
and without the novel complex treatment, and the surface morphology of the electrolytic
copper foil in both cases was visually observed as shown in Figure 8. It can be clearly
seen that there is an obvious bright band corresponding to the weld zone on the surface of
the electrolytic copper foil without the novel complex treatment, while there is no visible
bright band on the surface of the electrolytic copper foil with the novel complex treatment,
indicating that the quality of electrolytic copper foil can be greatly improved by the complex
treatment. In other words, the obvious bright bands disappeared, and the adverse impact
of longitudinal weld on the quality of electrolytic copper foil could be resolved by adopting
the novel complex treatment after welding.

Figure 8. Morphology of electrolytic copper foil by welded TA1 titanium cathode roller (a) Without
the novel complex treatment; (b) With the novel complex treatment.

4. Conclusions
In this study, TA1 with high purity was used as the research material, and a novel
complex treatment of heat treatment and sandblasting was primarily developed for reg-
ulating the microstructure of the weld zone and making the microstructure in the weld
Materials 2023, 16, 2149 9 of 10

zone close to that of the base metal. The results show that the difference between the weld
area and the base metal could be effectively decreased by the novel complex treatment,
and 650 ◦ C annealing had the optimal effect of refining the microstructure of the weld
zone, which could reduce the ratio of α phase’s length to width and reduce the microstruc-
ture difference between the weld zone and the base metal. At the same time, with the
increase of annealing temperature, the tensile strength and yield strength decreased by
about 10 MPa; the elongation after fracture increased by 20%; the average microhardness
of the WZ and the HAZ decreased by about 10 HV0.10 ; and that of the BM decreased by
about 3 HV0.10 . The heat treatment after welding effectively adjusted the properties of
the weld zone, reduced the hardness and strength, and improved the toughness. The
subsequent sandblasting after annealing further refined the grain size in the weld zone
and made the microstructure in the WZ close to that of the BM. Sandblasting increased the
surface hardness by about 45 HV0.10 . The annealing + sandblasting better refined the grain
size, improved its microstructure, and reduced the difference between the WZ structure
and the BM structure. Finally, the application test showed no visible bright band on the
surface of the electrolytic copper foil prepared by the welded titanium plate with the novel
complex treatment, which indicates that the quality of electrolytic copper foil can be greatly
improved by the complex treatment. Therefore, this study can provide valuable technical
support for the “welding” manufacturing of the titanium sleeve of the cathode roller.

Author Contributions: Conceptualization, X.A.; methodology, D.W.; software, D.W. and M.L.; valida-
tion, X.A. and W.W.; formal analysis, Y.X.; investigation, Y.X.; resources, D.W. and M.L.; data curation,
W.W.; writing—original draft preparation, Y.X.; writing—review and editing, J.H.; visualization, J.H.;
supervision, X.A. and W.W.; project administration, D.W. and M.L.; funding acquisition, J.H. All
authors have read and agreed to the published version of the manuscript.
Funding: This research was supported by the Priority Academic Program Development of Jiangsu
Higher Education Institutions (PAPD-3), the Top-notch Academic Program Projects of Jiangsu Higher
Education Institutions (TAPP), and the cooperation project.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data that support the findings of this study are available from the
corresponding author.
Conflicts of Interest: The authors declare no conflict of interest.

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