【Technical Field】
The present disclosure relates to a zinc (Zn) alloy plated
steel material having excellent weldability and deformed-part
10 corrosion resistance and to a method of manufacturing the same.
【Background Art】
Since zinc (Zn) plating, suppressing the corrosion of iron
(Fe) using cathodic protection, has excellent anti-corrosion
15 performance and economic efficiency, Zn plating has commonly
been used in manufacturing a steel material having high
corrosion resistance. In detail, in the case of hot dip
galvanized steel materials forming a plating layer in such a
manner that a steel material is immersed in molten Zn, the
20 manufacturing process thereof is simpler, and the prices of
products are cheaper than an electrogalvanized steel material.
Thus, demand for hot dip galvanized steel materials has
increased in the automobile industry, the household appliance
industry, the building materials industry, and other
25 industries.
Page 3
Hot dip galvanized steel materials plated with Zn may have
the characteristics of sacrificial corrosion protection in
which, when being exposed to a corrosion environment, Zn having
an oxidation reduction potential lower than that of Fe is first
5 corroded, so that the corrosion of steel materials is prevented.
In addition, Zn in a plating layer may be oxidized to generate
minute corrosion products on the surface of steel materials and
to block steel materials from an oxidizing atmosphere, thereby
improving corrosion resistance.
10 However, due to increased air pollution caused by
industrial development, an increase of corrosive environments
and strict regulations regarding resource conservation and
energy savings, there is a growing need for the development of
steel materials having better corrosion resistance than Zn
15 plated steel materials of the related art.
To this end, a large amount of research into technology
to manufacture Zn alloy plated steel materials having improved
corrosion resistance through adding elements, such as aluminum
(Al) and magnesium (Mg) to a galvanizing bath, has been
20 conducted. A large amount of research into a technology to
manufacture Zn-Al-Mg-based Zn alloy plated steel materials, as
a typical Zn alloy plated material, in which Mg is added to Zn-Al
plated materials has also been conducted.
However, such Zn-Al-Mg-based Zn alloy plated steel
25 materials have weaknesses as below.
First, when Zn-Al-Mg-based Zn alloy plated steel
Page 4
materials are welded, cracks caused by liquid metal
embrittlement (LME) may easily occur, thereby degrading
weldability thereof. In other words, in a case in which Zn alloy
plated steel materials described above are welded,
Zn-5 Al-Mg-based intermetallic compounds having a relatively low
melting point are dissolved and penetrate between grain
boundaries of the base steel.
Second, Zn-Al-Mg-based Zn alloy plated steel materials
have a low level of deformed-part corrosion resistance. In
10 other words, such Zn alloy plated steel materials may include
a large amount of Zn-Al-Mg-based intermetallic compounds
generated by thermodynamic interactions of Zn, Al, and Mg in
a plating layer. Since such intermetallic compounds have a
relatively high degree of hardness, cracks may be generated in
15 a plating layer during a bending process, thereby degrading
deformed-part corrosion resistance.
【Disclosure】
【Technical Problem】
20 An aspect of the present disclosure may provide a zinc
(Zn) alloy plated steel material having excellent weldability
and deformed-part corrosion resistance and a method of
manufacturing the same.
25 【Technical Solution】
Page 5
According to an aspect of the present disclosure, a zinc
(Zn) alloy plated steel material comprises a base steel and a
Zn alloy plating layer, the Zn alloy plating layer including,
by wt%, aluminum (Al): 0.1% to 5.0%, magnesium (Mg): 0.1% to
5 5.0%, Zn as a residual component, and inevitable impurities.
Between the base steel and the Zn alloy plating layer, a lower
interface layer formed on the base steel and having a fine
structure and an upper interface layer formed on the lower
interface layer and having a network-type structure or an
10 island-type structure are provided.
According to another aspect of the present disclosure,
a method of manufacturing a Zn alloy plated steel material
comprises providing a base steel; surface activating the base
steel; obtaining the Zn alloy plated steel material by immersing
15 the base steel that has been surface activated in a Zn alloy
plating bath including, by wt%, Al: 0.1% to 5.0%, Mg: 0.1% to
5.0%, Zn as a residual component, and inevitable impurities and
performing plating; and cooling the Zn alloy plated steel
material after gas wiping the Zn alloy plated steel material.
20
【Advantageous Effects】
According to an aspect of the present disclosure, a Zn
Page 6
alloy plated steel material has significantly excellent
weldability and deformed-part corrosion resistance.
【Description of Drawings】
5 FIG. 1 is a scanning electron microscope (SEM) image of
an interface layer of a zinc (Zn) alloy plated steel sheet
according to Inventive Example 1 of Exemplary Example 1.
FIG. 2 is an SEM image of an interface layer of a Zn alloy
plated steel sheet according to Comparative Example 1 of
10 Exemplary Example 1.
FIG. 3 is an SEM image of an interface layer of a Zn alloy
plated steel sheet according to Specimen Number 1 of Exemplary
Example 2.
FIG. 4 is an SEM image of an interface layer of a Zn alloy
15 plated steel sheet according to Specimen Number 2 of Exemplary
Example 2.
FIG. 5 is an SEM image of an interface layer of a Zn alloy
plated steel sheet according to Specimen Number 3 of Exemplary
Example 2.
20 FIG. 6 is an SEM image of an interface layer of a Zn alloy
plated steel sheet according to Specimen Number 4 of Exemplary
Example 2.
【Best Mode for Invention】
25 Hereinafter, a zinc (Zn) alloy plated steel material
Page 7
having excellent weldability and deformed-part corrosion
resistance according to an exemplary embodiment will be
described in detail.
A Zn alloy plated steel material according to an exemplary
5 embodiment includes a base steel and a Zn alloy plating layer.
In an exemplary embodiment, a type of the base steel is not
specifically limited, and the base steel may be provided as a
steel sheet or a steel wire rod. In the meantime, a Zn alloy
plating layer may be formed on a single surface or opposing
10 surfaces of the base steel.
In addition, in an exemplary embodiment, an alloy
composition of the base steel is not specifically limited.
However, in a case in which the base steel includes, a total
of 0.1 wt% or more of one or more type of surface enrichment
15 element selected from a group consisting of silicon (Si),
manganese (Mn), and nickel (Ni), a portion of surface enrichment
elements in the base steel is dissolved (a total of 0.001 wt%
or more) in an upper interface layer and a lower interface layer
formed between the base steel and a plating layer, thereby
20 maximizing an effect of an exemplary embodiment.
The Zn alloy plating layer may include, by wt%, aluminum
(Al): 0.1% to 5.0%, Mg: 0.1% to 5.0%, Zn as a residual component,
and inevitable impurities.
Mg in the Zn alloy plating layer is an element playing
25 a role in improving corrosion resistance of a plated steel
material. In a case in which an Mg content is significantly
Page 8
low, there may be a problem in which an effect of improving
corrosion resistance is insignificant. Thus, a lower limit
value of the Mg content in the Zn alloy plating layer may be
0.1 wt%, in detail, 0.5 wt%, and more specifically, 0.8 wt%.
5 However, in a case in which the Mg content is significantly high,
there is a problem in which dross of a plating bath caused by
oxidation of Mg in the plating bath may occur. Thus, an upper
limit value of the Mg content in the Zn alloy plating layer may
be 5.0 wt%, in detail, 3.0 wt%, and more specifically, 2.0 wt%.
10 Al in the Zn alloy plating layer is an element playing
a role in suppressing dross of an Mg oxide. In a case in which
an Al content is significantly low, an effect of preventing
oxidation of Mg in the plating bath is insignificant. Thus,
a lower limit value of the Al content in the Zn alloy plating
15 layer may be 0.1 wt%, in detail, 0.5 wt%, and more specifically,
0.8 wt%. However, in a case in which the Al content is
significantly high, there is a problem in which a temperature
of the plating bath should be raised. In a case in which the
temperature of the plating bath is relatively high, plating
20 equipment may be eroded. Thus, an upper limit value of the Al
content in the Zn alloy plating layer may be 5.0 wt%, in detail,
3.0 wt%, and more specifically, 2.0 wt%.
Between the base steel and the Zn alloy plating layer,
the lower interface layer formed on the base steel and having
25 a fine structure and the upper interface layer formed on the
lower interface layer and having a network-type structure or
Page 9
an island-type structure may be provided.
A crack of liquid metal embrittlement (LME) considered
to mainly be a problem during spot welding of the Zn alloy plated
steel material may be effectively suppressed by forming an
5 interface layer having a double layered structure, as described
above. Even in the case in which, a crack is generated on a
surface of the Zn alloy plating layer in a bending process,
bending workability may be improved by effectively preventing
the base steel from being outwardly exposed.
10 According to an exemplary embodiment, an area percentage
of the upper interface layer, as compared with an area of the
lower interface layer, may be in a range of 10% to 90%, in detail,
in a range of 20% to 80%, in more detail, in a range of 40% to
70%, and more specifically, in a range of 45% to 65%. In this
15 case, an area percentage refers to a ratio of an area of the
upper interface layer to an area of the lower interface layer,
when viewed from an upper portion of a steel material in a
thickness direction thereof, for example, in the case of a flat
surface, without considering three dimensional bending or the
20 like. In a case in which the area percentage of the upper
interface layer is less than 10%, the area of the upper interface
layer is significantly small, so that weldability and
deformed-part corrosion resistance of the Zn alloy plated steel
material may be degraded. On the other hand, in a case in which
25 the area percentage of the upper interface layer is more than
90%, a crack may be generated due to brittleness during a
Page 10
process.
In this case, whether the interface layer having the
double layered structure, as described above, has been formed
or not can be determined using a method below. In other words,
5 since the interface layer having the double layered structure
is present on an interface of the base steel and the Zn alloy
plating layer, there is a limitation in confirming a structure
thereof, or the like, in a case in which the Zn alloy plating
layer is not removed. Thus, after an entirety of the Zn alloy
10 plating layer was dissolved by dipping the Zn alloy plated steel
material in a chromic acid solution, chemically dissolving only
the Zn alloy plating layer on an upper portion of the upper
interface layer for 30 seconds, while the interface layer having
the double layered structure was not damaged, a scanning
15 electron microscope (SEM) image of a residual interface layer,
as described above, was taken, and it was determined whether
the interface layer having the double layered structure was
formed or not by analyzing an image, in order to measure a
thickness of each interface layer. In this case, as an example
20 to produce the chromic acid solution, the chromic acid solution
may be produced in such a manner that one liter of distilled
water is mixed with 200g of CrO3, 80g of ZnSO4, and 50g of HNO3.
In the meantime, a composition of each interface layer to be
subsequently described may be analyzed using energy dispersive
25 spectroscopy (EDS), while the area percentage of the upper
interface layer may be measured using an image analyzer.
Page 11
According to an exemplary embodiment, the upper interface
layer and the lower interface layer include an iron
(Fe)-Al-based alloy. The Fe-Al-based alloy may be provided as
one or more type of alloy selected from a group consisting of
Fe2Al5, 5 FeAl3, and FeAl. In this case, when the upper interface
layer and the lower interface layer include the Fe-Al-based
alloy, the Fe-Al-based alloy is included as a main component
(about 80 wt% or more), and the case in which other effective
components or inevitable impurities are included is not
10 excluded.
According to an exemplary embodiment, the upper interface
layer may include, by wt%, Al: 15% to 80%, Fe: 20% to 85%, and
Zn: 10% or less (including 0%), in detail, Al: 15% to 60%, Fe:
40% to 80%, and Zn: 10% or less (including 0%), and more
15 specifically, Al: 20% to 40%, Fe: 60% to 80%, and Zn: 10% or
less (including 0%).
In general, the Al content in an interface layer formed
at an interface between the Zn alloy plating layer and the base
steel is about 10 wt%. However, in the case of the Zn alloy
20 plated steel material according to an exemplary embodiment, the
Al content contained in the upper interface layer is relatively
high. In a case in which the Al content in the upper interface
layer is lower than 15%, an effect of reducing an LME crack may
be insignificant. On the other hand, in a case in which the
25 Al content is higher than 80%, a crack may be generated due to
brittleness during a process.
Page 12
According to an exemplary embodiment, a thickness of the
upper interface layer may be in a range of 50 nm to 1,000 nm,
in detail, in a range of 70 nm to 800 nm, in more detail, in
a range of 75 nm to 450 nm, and more specifically, in a range
5 of 90 nm to 420 nm. In a case in which the thickness of the
upper interface layer is less than 50 nm, the effect of reducing
the LME crack may be insignificant during welding. On the other
hand, in a case in which the thickness thereof is greater than
1,000 nm, an area of a crack may become greater during a process.
10 According to an exemplary embodiment, a thickness of the
lower interface layer may be 500 nm or less (excluding 0 nm),
in detail, 300 nm or less (excluding 0 nm), and more specifically,
100 nm or less (excluding 0 nm). In a manner different from
the upper interface layer, the lower interface layer should
15 conformally cover a front surface of the base steel. However,
in a case in which the thickness of the lower interface layer
is greater than 500 nm, the lower interface layer is unlikely
to be able to conformally cover a surface of the base steel.
In the meantime, on condition that the lower interface layer
20 conformally covers the surface of the base steel, in general,
when the thickness thereof is thinner, a degree of uniformity
thereof is increased. Thus, a lower limit value thereof is not
specifically limited.
The Zn alloy plated steel material according to an
25 exemplary embodiment described above may be manufactured using
various methods, and a manufacturing method thereof is not
Page 13
specifically limited. However, the Zn alloy plated steel
material may be manufactured using a method below as an
implementation example.
Hereinafter, a method of manufacturing the Zn alloy plated
5 steel material having excellent weldability and deformed-part
corrosion resistance according to another exemplary embodiment
will be described in detail.
Surface Activating
10 After a base steel is provided, the base steel is surface
activated. Surface activating base steel is performed to
easily form an Fe-Al-based alloy layer having a double layered
structure between the base steel and a Zn alloy plating layer.
According to an exemplary embodiment, a centerline
15 arithmetical average roughness (Ra) of a surface activated base
steel may be in a range of 0.8 μm to 1.2 μm, in detail, in a
range of 0.9 μm to 1.15 μm, and more specifically, in a range
of 1.0 μm to 1.1 μm. In this case, the centerline arithmetical
average roughness (Ra) refers to an average height from a
20 centerline (an arithmetical mean line of a profile) to a curve
of a cross section.
In addition, according to an exemplary embodiment, a ten
point median height (Rz) of the surface activated base steel
may be in a range of 7.5 μm to 15.5 μm. In this case, the ten
25 point median height (RZ) refers to a distance between two
parallel virtual lines passing through a third highest point
Page 14
and a third lowest point, respectively, in a roughness profile
taken in a reference length of a cut-off portion thereof and
parallel with the centerline.
In addition, according to an exemplary embodiment, a
5 maximum height roughness (Rmax) of the surface activated base
steel may be in a range of 8 μm to 16.5 μm. In this case, the
maximum height roughness (Rmax) refers to a distance between
two parallel virtual lines parallel with the centerline and
passing through a highest point and a lowest point of a curve
10 in the roughness profile taken in a reference length of a cut-off
portion thereof.
In a case in which surface roughnesses (Ra, Rz, and Rmax)
of the base steel is controlled to be within a range described
above, a reaction between the base steel and a plating solution
15 is relatively active, thereby easily forming an interface layer
having a double layered structure.
In an exemplary embodiment, a method of surface activating
the surface of the base steel is not specifically limited.
However, in detail, a plasma treatment or an excimer laser
20 treatment may be used. During plasma treatment or excimer laser
treatment, a specific processing condition is not specifically
limited. Any device and/or condition that may activate the
surface of the base steel to within a range described above may
be applied.
25 However, as a desirable example to activate the surface
of the base steel, a method below may be used.
Page 15
The surface activating the base steel may be performed
using plasma treatment on the condition of radio frequency (RF)
power in a range of 150 W to 200 W. In a case in which RF power
is controlled to be within a range described above, an area
5 percentage of an upper interface layer, as compared with an area
of a lower interface layer, may be optimized, thereby securing
excellent weldability and deformed-part corrosion resistance.
In addition, the surface activating the base steel may
be performed in an inert gas atmosphere. In this case, the inert
10 gas atmosphere may be provided as either a nitrogen gas (N2)
atmosphere or an argon (Ar) gas atmosphere. As such, in a case
in which the surface activating the base steel is performed in
the inert gas atmosphere, an oxide film present on the surface
of the base steel is removed, thereby improving reactivity of
15 the plating solution and the base steel. Thus, the Fe-Al-based
alloy layer having a double layered structure may be easily
formed between the base steel and the Zn alloy plating layer.
Forming Surface Oxide Layer
20 A surface oxide layer is formed on a surface of a base
steel by heat treating the base steel. However, in the case
of forming a surface oxide layer, if the base steel includes,
by wt%, a total of 0.1% or more of one or more of type of element
selected from a group consisting of Si, Mn, and Ni, surface
25 enrichment of Si, Mn, and Ni may be carried out, thereby
sufficiently dissolving Si, Mn, and Ni in an interface layer
Page 16
formed in a subsequent process. The forming a surface oxide
layer is not essential.
In the meantime, in a case in which the forming a surface
oxide layer is performed before obtaining a Zn alloy plated
5 steel material, a process order is not specifically limited.
For example, after surface activating the base steel, the
surface oxide layer may be formed in a surface activated base
steel. Alternatively, after the surface oxide layer is formed,
the base steel in which the surface oxide layer has been formed
10 may be surface activated.
According to an exemplary embodiment, during the heat
treating the base steel, a heat treatment temperature may be
in a range of 700°C to 900°C, and in detail, in a range of 750°C
to 850°C. In a case in which the heat treatment temperature
15 is lower than 700°C, an effect thereof may be insufficient. On
the other hand, in a case in which the temperature thereof is
higher than 900°C, process efficiency may be reduced.
Obtaining Zn Alloy Plated Steel Material
20 A surface activated base steel or a surface activated base
steel in which a surface oxide layer has been formed is immersed
in a Zn alloy plating bath including, by wt%, Al: 0.1% to 5.0%,
Mg: 0.1% to 5.0%, Zn as a residual component, and inevitable
impurities, and plating is performed, thereby obtaining a Zn
25 alloy plated steel material.
In this case, a temperature of a plating bath of the
Page 17
related art may be applied to a temperature of the Zn alloy
plating bath. In general, in a case in which an Al content,
among components in the plating bath, is increased, a melting
point is increased. Thus, internal equipment of the plating
5 bath is eroded, thereby causing a reduction in a lifespan of
a device and a defect on a surface of a Zn alloy plated steel
material due to an increase in dross of an Fe alloy in the plating
bath. However, since the Al content is controlled to be in a
range of 0.5 wt% to 3.0 wt%, a relatively low level, it is
10 unnecessary to set the temperature of the plating bath to be
relatively high, and the temperature of the plating bath of the
related art may be applied. In detail, the temperature thereof
may be in a range of 430°C to 480°C.
Subsequently, a coating weight is controlled using a gas
15 wiping treatment of the Zn alloy plated steel material. The
gas wiping treatment is to control the coating weight, and a
method thereof is not specifically limited. Air or N2 may be
used as a gas in this case, and it is more desirable to use N2
therebetween. In a case in which air is used, Mg may be first
20 oxidized on a surface of a plating layer, thereby causing a
defect on the surface of the plating layer.
Subsequently, the Zn alloy plated steel material, the
coating weight of which has been controlled, is cooled. In an
exemplary embodiment, during cooling described above, a cooling
25 rate and a cooling end temperature are not specifically limited
and may be set based on a cooling condition of the related art.
Page 18
In the meantime, during cooling described above, a cooling
method is not specifically limited. In detail, cooling may be
performed by using an air jet cooler, N2 wiping, by spraying
water mist, or the like.
5 Hereinafter, an exemplary embodiment will be described
in more detail using an exemplary example. However, an
exemplary embodiment below is intended to describe the present
disclosure in more detail through illustration thereof, but not
limit the scope of rights of the present disclosure, because
10 the scope of rights thereof is determined by the contents
written in the appended claims and reasonably inferred
therefrom.
【Industrial Applicability】
15 (Exemplary Example 1)
After, as a specimen for plating, a low carbon cold rolled
steel sheet having a thickness of 0.8 mm, a width of 100 mm,
and a length of 200 mm was provided, a surface thereof was surface
activated using a plasma treatment. In this case, Ra, Rz, and
20 Rmax of the surface activated base steel are illustrated in
Table 1 below. Subsequently, the surface activated base steel
was immersed in a Zn alloy plating bath having a composition
in Table 1 below, thereby manufacturing a Zn alloy plated steel
material. Subsequently, a coating weight was controlled to be
70 g/m2 25 per side by gas wiping the Zn alloy plated steel material,
and the Zn alloy plated steel material was cooled to a room
Page 19
temperature (about 25°C) at an average cooling rate of 10°C/sec.
Subsequently, a composition, a thickness, and an area
percentage of an interface layer of each manufactured Zn alloy
plated steel material were measured, and results thereof are
5 illustrated in Table 1 below. A measuring method is the same
as a case described above.
Subsequently, weldability and deformed-part corrosion
resistance of each manufactured Zn alloy plated steel material
were assessed, and results thereof are illustrated in Table 2
10 below.
Weldability was assessed using a method below.
A welding current of 7 kA was applied using a copper
(Cu)-chrome (Cr) electrode having a tip diameter of 6 mm, and
welding was performed on the condition of electrode force of
15 2.1 kN, a welding time of 11 cycles (in this case, 1 cycle refers
to 1/60 second and is the same, hereinafter) and a holding time
of 11 cycles. In each exemplary example, a total of five
specimens were produced. Lengths of an entirety of LME cracks
occurring in five specimens were measured, and an average length
20 of LME cracks and a maximum length of LME cracks were obtained.
As a result, in a case in which the average length of LME cracks
was 20 μm or less, a specimen was assessed to be “GO”. In a
case in which the average length of LME cracks was greater than
20 μm, a specimen was assessed to be “NG”. In a case in which
25 the maximum length of LME cracks was 100 μm or less, a specimen
was assessed to be “GO”. In a case in which the maximum length
Page 20
of LME cracks was greater than 100 μm, a specimen was assessed
to be “NG”.
Deformed-part corrosion resistance was assessed using a
method below.
5 After a bending process (0T bending) of each Zn alloy
plated steel material at 180°C, each bending-processed Zn alloy
plated steel material was charged into a salt spray testing
instrument, and a red rust occurrence time was measured based
on international standard (ASTM B117-11). In this case, 5% salt
10 water (at a temperature of 35°C and a pH of 6.8) was used, and
2 ml/80cm2 of water was sprayed per hour. In a case in which
the red rust occurrence time was 500 hours or more, the Zn alloy
plated steel material was assessed to be “GO”. In a case in which
the red rust occurrence time was shorter than 500 hours, the
15 Zn alloy plated steel material was assessed to be “NG”.
【Table 1】
Remar
ks
Surface
Roughn
ess
(μm)
Composition
of Plating
Bath (wt%)
Upper Interface
Layer
Lower
Interface
Layer
Al Mg Composi
tion
(wt%)
Thi
ckn
ess
(nm
Perce
ntage
(area
%)
Compos
ition
(wt%)
Thick
ness
(nm)
Page 21
)
Inven
tive
Examp
le 1
Ra: 1.04
Rz: 8.57
Rmax:
10.5
1 1 Al:
20.10
Fe:
77.63
Zn: 1.11
830 25 Al:
9.8
Fe:
88.8
Zn:
1.35
80
Compa
rativ
e
Examp
le 1
Ra: 0.56
Rz: 9.26
Rmax:
13.7
1 1 - - - Al:
10.3
Fe:
88.65
Zn:
1.01
50
Compa
rativ
e
Examp
le 2
Ra: 1.57
Rz: 15.2
Rmax:12
.8
1.6 1.6 - - - Al:
12.5
Fe:
86.34
Zn:
1.15
60
【Table 2】
Remarks Weldability Deformed-part
Corrosion
Resistance
Average Length of Maximum Length of Red Rust
Page 22
LME Cracks (μm) LME Cracks (μm) Occurrence
Time
(h)
Inventiv
e
Example
1
18 GO 94 GO 500 GO
Comparat
ive
Example
1
30 NG 179 NG 300 NG
Comparat
ive
Example
2
34 NG 125 NG 350 NG
With reference to Tables 1 and 2, it can be confirmed that,
in the case of Inventive Example 1 satisfying an entirety of
conditions of an exemplary embodiment, an average length of LME
5 cracks is 20 μm or less, a maximum length of LME cracks is 100
μm or less, and weldability is excellent. In addition, a red
rust occurrence time is 500 hours or more, and deformed-part
corrosion resistance is significantly excellent. In the
meantime, it can be confirmed that, in the case of Comparative
10 Examples 1 and 2, weldability and deformed-part corrosion
resistance was degraded, since an interface layer having a
Page 23
double layered structure was not formed.
In the meantime, FIG. 1 is an SEM image of an interface
layer of a Zn alloy plated steel sheet according to Inventive
Example 1 of Exemplary Example 1. FIG. 2 is an SEM image of
5 an interface layer of a Zn alloy plated steel sheet according
to Comparative Example 1 of Exemplary Example 1.
(Exemplary Example 2)
In order to assess a change in an area percentage of an
10 upper interface layer depending on a condition of plasma
treatment and weldability and deformed-part corrosion
resistance of a Zn alloy plated steel material due to the change,
the Zn alloy plated steel material was manufactured while other
conditions were the same as those of Exemplary Example 1, and
15 only a composition of a plating bath (Al of 1.4 wt%, Mg of 1.4
wt%, and Zn as a residual component) and a condition of plasma
treatment were different. The condition of plasma treatment
in each example is illustrated in Table 3 below.
Subsequently, a composition, a thickness, and an area
20 percentage of an interface layer of each manufactured Zn alloy
plated steel material were measured, and results thereof are
illustrated in Table 3 below. A measuring method is the same
as a case described above.
Subsequently, weldability and deformed-part corrosion
25 resistance of each manufactured Zn alloy plated steel material
Page 24
were assessed, and results thereof are illustrated in Table 4
below. An assessment method is the same as a case described
above.
【Table 3】
Speci
men
No.
Condition of
Plasma
Treatment
Upper Interface Layer Lower
Interface
Layer
RF
Power
(W)
Atmos
phere
Compo
sitio
n
(wt%)
Thick
ness
(nm)
Perce
ntage
(area
%)
Compo
sitio
n
(wt%)
Thick
ness
(nm)
1 50 Air Al:16
Fe:81
.5
Zn:2.
5
25 36 Al:11
.5
Fe:82
.9
Zn:5.
6
60
2 100 N2 Al:25
Fe:71
.9
Zn:3.
1
55 24 Al:18
.4
Fe:78
Zn:3.
6
55
3 150 N2 Al:25
.3
Fe:72
150 48 Al:26
.4
Fe:72
60
Page 25
.2
Zn:2.
5
.1
Zn:1.
5
4 200 Ar Al:46
.2
Fe:50
.2
Zn:3.
6
350 61 Al:16
.4
Fe:81
.8
Zn:1.
8
55
5 250 Ar Al:79
Fe:15
.2
Zn:5.
8
460 72 Al:9.
8
Fe:86
.7
Zn:3.
5
55
【Table 4】
Specimen
No.
Weldability Deformed-p
art
Corrosion
Resistance
Average
Length of
LME Cracks
(μm)
Maximum
Length of
LME Cracks
(μm)
Red Rust
Occurrence
Time
(h)
Page 26
1 28.6 102.5 500
2 18.8 96.7 550
3 11 68 800
4 9.4 59 900
5 8.5 57 600
With reference to Tables 3 and 4, it can be confirmed that,
in the case of specimens 3 and 4 in which an area percentage
of an upper interface layer was controlled to be within a range
5 of 40% to 70%, weldability and deformed-part corrosion
resistance was significantly excellent as compared with other
specimens.
FIG. 3 is an SEM image of an interface layer of a Zn alloy
plated steel sheet according to Specimen Number 1 of Exemplary
10 Example 2. FIG. 4 is an SEM image of an interface layer of a
Zn alloy plated steel sheet according to Specimen Number 2 of
Exemplary Example 2. FIG. 5 is an SEM image of an interface
layer of a Zn alloy plated steel sheet according to Specimen
Number 3 of Exemplary Example 2. FIG. 6 is an SEM image of an
15 interface layer of a Zn alloy plated steel sheet according to
Specimen Number 4 of Exemplary Example 2.
While exemplary embodiments have been shown and described
above, it will be apparent to those skilled in the art that
modifications and variations could be made without departing
20 from the scope of the present invention as defined by the
appended claims.

【WE CLAIM:】
【Claim 1】
A zinc (Zn) alloy plated steel material, comprising:
5 a base steel and a Zn alloy plating layer, the Zn alloy
plating layer including, by wt%, aluminum (Al): 0.1% to 5.0%,
magnesium (Mg): 0.1% to 5.0%, Zn as a residual component, and
inevitable impurities,
wherein between the base steel and the Zn alloy plating
10 layer, a lower interface layer formed on the base steel and
having a fine structure and an upper interface layer formed on
the lower interface layer and having a network-type structure
or an island-type structure are provided.
15 【Claim 2】
The Zn alloy plated steel material of claim 1, wherein
the upper interface layer and the lower interface layer comprise
an Fe-Al-based alloy, and the Fe-Al-based alloy is provided as
one or more type of alloy selected from a group consisting of
20 Fe2Al5, FeAl3 and FeAl.
【Claim 3】
The Zn alloy plated steel material of claim 1, wherein
an area percentage of the upper interface layer, as compared
25 with an area of the lower interface layer, is in a range of 10%
Page 28
to 90%.
【Claim 4】
The Zn alloy plated steel material of claim 1, wherein
5 an area percentage of the upper interface layer, as compared
with an area of the lower interface layer, is in a range of 40%
to 70%.
【Claim 5】
10 The Zn alloy plated steel material of claim 1, wherein
the upper interface layer includes, by wt%, Al: 15% to 80%, Fe:
20% to 85%, and Zn: 10% or less (including 0%).
【Claim 6】
15 The Zn alloy plated steel material of claim 1, wherein
a thickness of the upper interface layer is in a range of 50
nm to 1,000 nm.
【Claim 7】
20 The Zn alloy plated steel material of claim 1, wherein
a thickness of the upper interface layer is in a range of 74
nm to 450 nm.
【Claim 8】
25 The Zn alloy plated steel material of claim 1, wherein
Page 29
a thickness of the lower interface layer is 500 nm or less
(excluding 0 nm).
【Claim 9】
5 The Zn alloy plated steel material of claim 1, wherein
the base steel comprises, by wt%, a total of 0.1% or more of
one or more type of element selected from a group consisting
of silicon (Si), manganese (Mn), and nickel (Ni), and the upper
interface layer and the lower interface layer further comprise
10 0.001% or more of one or more type of element selected from a
group consisting of Si, Mn, and Ni.
【Claim 10】
A method of manufacturing a Zn alloy plated steel material,
15 comprising:
providing a base steel;
surface activating the base steel;
obtaining the Zn alloy plated steel material by immersing
the base steel that has been surface activated in a Zn alloy
20 plating bath including, by wt%, Al: 0.1% to 5.0%, Mg: 0.1% to
5.0%, Zn as a residual component, and inevitable impurities and
performing plating; and
cooling the Zn alloy plated steel material after gas
wiping the Zn alloy plated steel material.
25
【Claim 11】
Page 30
The method of claim 10, wherein a centerline arithmetical
average roughness (Ra) of the base steel that has been surface
activated is in a range of 0.8 μm to 1.2 μm, a ten point median
height (Rz) is in a range of 7.5 μm to 15.5 μm, and a maximum
5 height roughness (Rmax) is in a range of 8 μm to 16.5 μm.
【Claim 12】
The method of claim 10, wherein the surface activating
the base steel is performed using a plasma treatment or an
10 excimer laser treatment.
【Claim 13】
The method of claim 10, wherein the surface activating
the base steel is performed by plasma treatment on a condition
15 of radio frequency (RF) power in a range of 150 W to 200 W.
【Claim 14】
The method of claim 10, wherein the surface activating
the base steel is performed in an inert gas atmosphere.
20
【Claim 15】
The method of claim 14, wherein the inert gas atmosphere
is provided as one among a nitrogen gas (N2) atmosphere, an
argon (Ar) gas atmosphere, and a mixed N2 and Ar gas atmosphere.
25
Page 31
【Claim 16】
The method of claim 10, wherein the base steel comprises,
by wt%, a total of 0.1% or more of one or more type of element
selected from a group consisting of Si, Mn, and Ni.
5 【Claim 17】
The method of claim 16, further comprising forming a
surface oxide layer in such a manner that the base steel that
has been surface activated is heat treated before the base steel
that has been surface activated is immersed in the Zn alloy
10 plating bath.
【Claim 18】
The method of claim 16, further comprising forming a
surface oxide layer in such a manner that the base steel is heat
treated before the base steel is surface activated.
15 【Claim 19】
The method of claim 17 or 18, wherein a heat treatment
temperature is in a range of 700°C to 900°C during the heat
treatment.