*Corr. Author’s Address: Wroclaw University of Science and Technology, Faculty of Mechanical Engineering, Department of Metal Forming,  
Welding Technology and Metrology, Lukasiewicza 7-9, 50-371 Wroclaw, Poland, marzena.lachowicz@pwr.edu.pl
493
Strojniški vestnik - Journal of Mechanical Engineering 68(2022)7-8, 493-505 Received for review: 2022-03-31
© 2022 The Authors. CC BY 4.0 Int. Licensee: SV-JME Received revised form: 2022-05-30
DOI:10.5545/sv-jme.2022.142 Original Scientific Paper Accepted for publication: 2022-06-01
Effect of Dual-stage Ageing and RRA Treatment  
on the Three-body Abrasive Wear of the AW7075 Alloy
Lachowicz, M.M. − Leśniewski, T. − Lachowicz, M.B.
Marzena M. Lachowicz
*
 − Tadeusz Leśniewski − Maciej B. Lachowicz
Wroclaw University of Science and Technology, Faculty of Mechanical Engineering, Poland
The paper presents an analysis of the influence of the heat treatment state on the abrasive wear of the AW7075 aluminium alloy. To determine 
the hardening state, the material hardness was measured. It was found that hardness is not the only factor that influences this type of wear. 
For this reason, the influence of the emerging microstructure is also analysed in the considerations. After tribological tests, microscopic 
observations of surface features were carried out to determine the dominant mechanisms of surface damage. The results were extended by 
the hardness distribution carried out on the cross-section. There were no changes in hardness that could be related to either strain hardening 
or structural changes caused by friction.
Keywords: aluminium alloys, AW7075, abrasive wear, heat treatment, hardness, microstructure
Highlights
• 	 The hardness of the AW7075 alloy is not the only determinant of abrasive wear; with the microstructure of the tested alloy and 
the related heat treatment, the state also plays an important role in this respect.
• 	 The abrasive wear of the tested alloy can be ranked in the following order according to the heat treatment condition: dual ageing 
< RRA treatment < T6 state.
• 	 The wear features show a similar type of damage, regardless of the heat treatment state. Scratches, grooves, microcracks, and 
slight plastic deformation features be observed on the wear surface.
• 	 Decohesion developed mainly around grain boundaries and interfacial boundaries, which facilitates the loss of continuity with 
the matrix in the presence of coherent particles. Larger and incoherent precipitates in the matrix can act as an abrasive and 
increase the wear rate.
• 	 The presence of large particles of the primary phases, which do not dissolve at the stage of heat treatment, promotes their 
crushing and defragmentation during abrasive wear.
• 	 The surface hardness does not change due to the occurrence of mechanical effects resulting from friction.
0  INTRODUCTION
There is relative movement between surfaces of 
components in some applications of aluminium 
alloys. Wear resistance then becomes an important 
property to consider. Numerous research studies show 
that heat treatment can have a significant impact on 
tribological wear. In particular, the fragmentation of 
the microstructure components can significantly affect 
the obtained tribological parameters [1] to [3].
The presence of intermetallic phases in the 
microstructure offers a wide spectrum of possibilities 
for the strengthening of aluminium alloys. This group 
also includes the high-strength 7000 series alloys. Two 
treatments are used for this purpose: supersaturation 
and subsequent ageing. The sequence for ageing the 
7000 series alloys is given as follows: solid solution 
(a) → Guinier-Preston (GP) zones → η’ (MgZn
2
) 
→ η (MgZn
2
) [4] and [5]. The typical hardness-
ageing diagram for a heat-treatable aluminium alloy 
is shown in Fig. 1. GP zones are formed during 
ageing at room temperature or the early stages of 
ageing. They are fully coherent with the matrix. The 
greatest hardening effect is achieved at the stage of 
separation of the intermediate phase, which is related 
to the change in the mechanism of the interaction of 
the precipitates with dislocations. This is a typical T6 
state. The stresses that are needed to cut the particles 
by dislocation, as well as the stresses caused by the 
Orowan mechanism associated with the formation of 
a dislocation loop around these precipitates, obtain 
their maximum values. The material hardness drops 
significantly when there is a complete loss of the 
coherence of the precipitates. Ageing to the T6 state 
is associated with a continuous distribution of grain 
boundary precipitates (GBPs) [6] and [7]. A properly 
carried out heat treatment should end at the stage of 
forming the matrix of precipitates (MPs), which is 
partially coherent with the intermediate phase η'.
The T6 state is characterized by high strength and 
hardness but is highly susceptible to stress corrosion 
cracking. When looking for greater resistance to 
this type of corrosion, dual-stage ageing (DA) and 
Retrogression and Re-Ageing (RRA) treatment 
are used [9] to [13]. The first stage of DA ageing is 
characterized by a lower temperature when compared 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)7-8, 493-505
494 Lac ho wicz,	M.M.	−	Leśnie wski,	T .	−	Lac ho wicz,	M.B.
to conventional ageing, and it is responsible for the 
diffusion and homogeneous distribution of the GP 
zones. The coarse-grained GP zones and phases are 
formed during the second ageing and contribute to 
the peak hardness. MPs are coarser and partially 
incoherent with phase η when compared to one-
step ageing. This helps to reduce the hardness of the 
alloy [12] and [13]. Another solution is the multi-
stage RRA heat treatment. Retrogression involves 
heating the alloy, which had earlier been hardened, at 
a temperature in the range of 200 ºC to 260 ºC for a 
short period (120 s), and then re-ageing the alloy to a 
condition typical for the T6 state. The use of the RRA 
treatment leads to the obtaining of a microstructure 
that is characterized by the presence of fine-dispersed 
and coherent η’ (MgZn
2
) MPs. They are characteristic 
of the T6 state. However, at the GBPs there are 
fragmented and discontinuous precipitations that 
are typical for T7 over-ageing. As a result, the grain 
boundary that is line blocked with continuous GBPs 
particles, as in the T6 state, is transformed into a state 
in which the precipitates of the η phase are coarse 
and discontinuous [9], [14], and [15]. After the RRA 
treatment, a larger fraction of the GBPs was observed 
[7]. Also, the copper content of GBPs increases with 
the time of heat treatment [6]. 
Fig. 1.  Schematic illustration of the precipitate strengthening 
contributions as a function aging time (based on [8])
The effect of heat treatment of aluminium alloys 
on their strength is already known. Its influence 
on the resistance to structural corrosion is also well 
understood [12] to [16]. Retrogression and re-ageing 
treatment improve the resistance to stress corrosion 
cracking (SCC) [6], while maintaining high strength, 
until the MPs become coarse [6]. However, the 
microstructure changes caused by heat treatment 
affect other functional properties of aluminium alloys. 
The high strength is maintained as long as the MPs 
are not coarse [6]. The RRA state is characterized 
by high resistance to fatigue crack initiation and 
better impact toughness as a result of the increased 
discretion of the precipitates occurring at the grain 
boundaries [9], [17] and [18]. Coarse GBPs also 
increase electrical conductivity [9]. The DA state, 
in terms of microstructure, brings the alloy closer to 
the over-ageing condition, which in turn results in a 
reduction in strength and an increase in ductility [19]. 
It seems obvious that the different hardnesses obtained 
for individual states should also affect the tribological 
wear. For this reason, in the present study, it was 
decided to consider the influence of microstructure on 
the abrasive wear of the AW 7075 aluminium alloy.
1  MATERIAL AND METHODS
The tests were carried out on the AW 7075 aluminium 
alloy. The chemical composition of the alloy, which 
was determined by GDS-500A Leco glow discharge 
optical spectrometry (GD OES), is shown in Table 1.
In the microstructure of all the tested samples, 
α(Al) solid solution was observed with grey, large 
precipitates of the α-AlFeMnSi phase, and dark 
primary precipitates of the Mg
2
Si phase (Fig. 2). The 
type of these particles was determined on the basis of 
the EDS results conducted as part of the preliminary 
studies and compared with the literature data. The 
grains of the solid solution were heterogeneous in 
nature and were surrounded by large precipitates 
of the iron-rich phase. The main changes in the 
microstructure, which were caused by the applied 
heat treatment, concern the morphology, size, 
quantity, and coherence of the formed precipitates. 
For this reason, the microstructure of the material in 
the image of the light microscope was of a similar 
nature. These changes are subtle and can, therefore, 
only be observed with the use of transmission electron 
microscopy (TEM) methods. However, it can be seen 
that in the case of the DA state, the precipitations of 
the strengthening phases are more clearly visible, 
which indicates their larger dimensions.
Table 1.  Chemical composition of the tested AW7075 aluminium alloy
Element Zn Mg Cu Fe Cr Si Mn Ti Al
Content [%] 5.42 2.34 1.45 0.39 0.26 0.12 0.10 0.03 rest

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495 Effect of Dual-stage Ageing and RRA Treatment on the Three-body Abrasive Wear of the AW7075 Alloy 
The parameters of three various heat treatments 
were developed for 30 mm × 100 mm sections with 
a thickness of 10 mm that were cut from the tested 
alloy (Fig. 3). The microstructure was investigated on 
conventionally prepared metallographic microsections 
using a Leica DM6000M light microscope. The tests 
were carried out before and after etching with a 10 % 
aqueous solution of HF. To determine the material 
hardening, BHN hardness measurements were carried 
out using the Brinell method and a DuraJet G5 
hardness tester (Struers).
To determine the abrasive wear resistance, tests 
were carried out on the T-07 tester made at the Institute 
of Sustainable Technology in Radom (Poland). The 
tribological tests were performed in the presence of 
the loose F90 electro-corundum abrasive, and all the 
tested samples were subjected to the same friction 
conditions. The used abrasive reflects the penetration 
of aluminium oxide or anodic coatings into the friction 
area very well. The oxide film is thin and can break 
off easily, in turn producing wear debris particles. The 
removal of the protective layer also accelerates the 
corrosive effects [20]. The method complied with the 
requirements of the GOST 23.208-79 standard [21]. 
The tested system consisted of a sample (plate) 
made of the tested material, and a counter-sample 
(roll) with a rubber ring. During the test, the material 
sample was pressed with a defined force of (F
N
) to a 
rubber disk with a diameter of d = 50 mm, which was 
rotating at a constant speed (n). Gravity was used to 
deliver a loose abrasive between the rotating disc and 
the fixed sample. In the presence of loose abrasive, 
the sample of the tested materials and the reference 
sample were subjected to abrasive wear under the 
used operating conditions, i.e., rotational speed n = 
60 rpm/min, test time t, and F
N
 loads in accordance 
with the above standard (t = 10 min, F = 44 N). The 
reference sample was grade C45 normalized steel. 
Next, the mass loss of the reference sample (Z
ww
) 
and the mass loss of the tested materials (Z
wb
) were 
a)   b)   c) 
Fig. 2.  Microstructure after; a) T6, b) DA, and c) RRA, light microscopy, etched with 10 % HF
Fig. 3.  Flow chart for the heat treatment process; a) T6, b) DA, and c) RRA

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)7-8, 493-505
496 Lac ho wicz,	M.M.	−	Leśnie wski,	T .	−	Lac ho wicz,	M.B.
determined. The mass loss of the samples (weight 
difference before and after the tests) was determined 
after a defined test time (determined by the number 
of rotations of the rubber roller). Based on the mass 
loss measurements, the abrasive wear resistance index 
K
b
 (relative wear resistance) was calculated from the 
following equation (Eq. (1)):
 K
ZN
ZN
b
ww bb
wb ww





, (1)
where Z
ww 
is the mass loss of the reference material 
(C45 steel), Z
wb
 the mass loss of the tested material, 
ρ
w
 the density of the reference material, ρ
b 
 the density 
of the tested material, N
w 
the number of revolutions 
of the reference material’s friction path, and N
b
 the 
number of revolutions of the tested material’s friction 
path. The density of the tested material (AW 7075) 
was 2.81 g/cm³.
The morphology of the specimens after the 
tribological tests was observed using scanning 
electron microscopy (SEM), which also identified the 
wear features. The Phenom World ProX microscope 
was used for this purpose. Backscattered electrons 
(BSE) and second electrons (SE) detectors with an 
accelerating voltage of 15 kV were used.
2  RESULTS AND DISCUSSION
2.1  Hardness Measurements
Based on the performed measurements, it can be 
stated that the proposed heat treatment contributed 
to the material strengthening (Fig. 4). It was found 
that the Brinell hardness (BHN) of the AW7075 alloy 
increases in the following order: DA<T6<RRA. The 
highest hardness of the AW7075 alloy was obtained 
after the RRA heat treatment, while the alloy that 
was heat treated to the T6 state had a slightly lower 
hardness. The use of double-stage ageing adversely 
affected the alloy strengthening, with the hardness 
after this process being the lowest.
Fig. 4.  Results of hardness measurements of the AW 7075 alloy 
after various heat treatments
2.2  Abrasive Wear
The AW 7075 aluminium alloy, with different levels of 
hardness obtained by heat treatment, was tested. Figs. 
5 and 6 present the three-body dry abrasion of the AW 
7075 alloy, which was determined as the weight loss 
for its heat-treated state. The results of the hardness 
and abrasive wear measurements can be summarized 
as follows:
• the abrasive wear kinetics of the T6 state were 
lower than for the DA and RRA states,
• the DA and RRA states, despite having different 
hardness values, had a comparable wear 
resistance, 
• the hardest sample (RRA state) had worse wear 
resistance than the one with lower hardness (T6 
state).
Fig. 5.  Mass loss (Z
wb
) results obtained for the AW 7075 alloy 
after various heat treatments
Fig. 6.  K
b
 factor obtained for the AW 7075 alloy  
after various heat treatments
Linear wear low theory (also called Archard’s 
equation) indicates the relationship between the 
hardness of the material and its abrasive wear 
resistance. In the case of the alloys in the DA state 
with the lowest hardness, the greatest weight loss, 
and thus the lowest wear resistance, was observed. 
However, in the remaining cases, this relationship did 
not work. Other authors also note that the correlation 
between hardness and wear resistance is not always 

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497 Effect of Dual-stage Ageing and RRA Treatment on the Three-body Abrasive Wear of the AW7075 Alloy 
clear [22] to [24]. However, Archard did not consider 
the role of the microstructure as one of the key factors 
in abrasive wear.
The conducted research shows that the hardness 
of the AW 7075 alloy is not the only factor that 
determines its wear. No linear relationship was 
observed between the hardness of the material and 
its wear; therefore, it can be concluded that the 
wear is also determined by the microstructure of the 
material. From the point of view of the microstructure, 
aluminium alloys can be considered as “composites” 
that consist of a soft matrix and hard precipitates 
formed during the heat treatment stage, which in turn 
affect the hardness and strength of these alloys. The 
presence of hard particles in the matrix effectively 
reduces wear [25] and [26]. Microstructural parameters 
(e.g., the hardness, shape, size, volume fraction, and 
distribution of the second phases), the properties of 
a)             
b)             
c)             
Fig. 7.  General views of the wear features after the different heat treatments; a) T6, b) DA, and c) RRA, SEM

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498 Lac ho wicz,	M.M.	−	Leśnie wski,	T .	−	Lac ho wicz,	M.B.
the matrix, and the interfacial bonding between the 
second phase and the matrix significantly influence 
the abrasive wear resistance [27]. Even a subtle change 
in the size and distribution of these precipitates can 
significantly affect the AW7075 alloy’s operational 
properties.
It is not difficult to observe that the wear was 
lower in the states in which the microstructure mainly 
shows significant precipitation that is coherent with 
the matrix (T6 state). Literature data clearly indicate 
that in the T6 condition, GBPs are mainly continuous 
and coherent particles [6] and [7]. The hardening 
peak caused by the presence of coherent phases is 
also confirmed by hardness measurements (Fig. 
4). During micro-ploughing, the metallic material 
is mainly elastically-plastically deformed, and it 
flows around and beneath the sliding particle [27]. 
In an ideal case, micro-ploughing, due to a single 
pass of one abrasive particle, does not result in any 
detachment of material from the wearing surface. A 
prow is formed ahead of the abrading particle, and the 
material is continuously displaced sideways to form 
ridges adjacent to the produced groove. As shown in 
Fig. 1, the particles coherent with the matrix will be 
sheared in accordance with the Friedel effect. This is 
conducive to maintaining the continuity of the matrix 
as well as the precipitations. Consequently, these 
particles are more difficult to detach from the matrix. 
In this situation, the wear will be mainly caused by 
foreign abrasive particles that are involved in the 
abrasion, which contributes to reduced consumption 
and higher K
b
 ratios. For both the RRA treatment and 
the T6 state, the particles that are partially coherent 
with the matrix constitute a significant contribution to 
the microstructure. The high degree of strengthening 
after RRA treatment is confirmed by high hardness 
(Fig. 4). However, after RRA treatment, the MPs are 
similar to those occurring in the T6 state [6], [7], [9], 
[14], and [15]. The grain boundaries are close to the 
over-ageing state. The GBPs consist of incoherent, 
discontinuous, and coarse precipitations [6], [7], [9], 
[14], [15], and [19]. In a situation in which a significant 
amount of precipitation is incoherent with the matrix, 
their presence in the microstructure may contribute 
to the decohesion of the material. However, it has 
been proved that a too high concentration of MPs 
deteriorates the resistance to stress corrosion cracking 
[6]. Material may be ploughed aside repeatedly by 
displacing particles, which may then detach due to 
micro-fatigue. The precipitations torn out in this 
a)              b) 
Fig. 8.  W ear	mo r pho lo gy	af t er	the	T6	heat	treatment;	SEM;	a)	BSE,	and	b)	SE
Fig. 9.  a) Exemplary SEM 3D-profilometry image, and b) surface texture of the wear tracks after the T6 heat treatment

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499 Effect of Dual-stage Ageing and RRA Treatment on the Three-body Abrasive Wear of the AW7075 Alloy 
a)               b) 
Fig. 10. W ear	mo r pho lo gy	af t er	D A ,	SEM	a)	BSE,	and	b)	SE
Fig. 11.  a) Exemplary SEM 3D-profilometry image, and b) the surface texture of the wear tracks after the DA heat treatment
a)              b) 
Fig. 12.  W ear	mo r pholo gy	af t er	RRA ,	SEM	a)	BSE,	and 	b)	SE
Fig. 13.  a) Exemplary SEM 3D-profilometry image, and b) the surface texture of the wear tracks after the RRA heat treatment

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500 Lac ho wicz,	M.M.	−	Leśnie wski,	T .	−	Lac ho wicz,	M.B.
a)              b) 
Fig. 14.  Wear morphology after DA; the wedge formation is visible locally; a) SEM image, and b) SEM 3D-profilometry image
a)              b) 
c)              d) 
Fig. 15.  Micro-ploughing of the surface is visible in the heat treatment state;  
a) DA, SEM image, b) DA, SEM 3D-profilometry image, c) RRA, SEM image, and d) RRA, SEM 3D-profilometry image
way, while moving in the mass of the material, may 
contribute to increased wear. V olume loss may occur 
as a result of the action of many abrasive particles. 
2.3  Wear Surface
To understand the reason for the different wear 
mechanisms better and to study the influence of matrix 
hardness on the wear performance, the morphology 
of the wear track was examined using SEM analysis. 

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501 Effect of Dual-stage Ageing and RRA Treatment on the Three-body Abrasive Wear of the AW7075 Alloy 
The analyses of the wear paths revealed the same 
type of damage in all the tested alloy states (Fig. 7), 
with the wear being abrasive. As shown in the images 
obtained at higher magnifications: grooves and 
scratches, microcracks, and plastic deformation can 
be easily observed on the surface of the wear tracks 
(Figs. 8 to 13). The resulting surface irregularities 
ranged from 4 µm to 6 µm, regardless of the heat 
treatment condition (Figs. 9, 11 and 13). The main 
wear mechanisms are therefore controlled by wedge 
formation and micro-ploughing (Figs. 14 and 15). 
However, this causes a large amount of ploughed 
material to embed into the matrix at the edge of the 
wear mark, which makes a significant contribution to 
material fatigue. Moreover, the abrasive material cuts 
the surface of the matrix. The grooves and scratches 
that are formed are not always parallel to the direction 
of friction, which indicates the displacement of 
the friction particles in the wear area (Fig. 7). The 
precipitations can increase hardness, but at the same 
time enhance the wear rate by causing disruption of 
plastic flow during particle impact. The larger ones 
can also act as an abrasive and, in turn, increase the 
wear rate during abrasion.
2.4 Subsurface Wear Morphology of the Samples and 
Microhardness Measurements
Observations of the wear surface carried out on the 
cross-section confirm the presented thesis (Figs. 
16 to 20). In the case of the DA state, more even 
wear was observed but, at the same time, it was 
often accompanied by delamination, which in turn 
contributed to the removal of larger fragments of the 
wear material (Figs. 18 and 19). It is unlikely that the 
fragments observed in the microscopic image came 
from surface micro-cutting, as this mechanism was 
not observed on the surface in the SEM investigations. 
This undoubtedly contributed to the greater wear 
observed during the tribological tests. 
As indicated earlier, the key factor was the 
microstructure. Observations on the perpendicular 
cross-section of the samples showed that decohesion 
developed mainly in the area of the grain boundaries 
and interfacial boundaries (Figs. 16b, 18b and 20c). 
The loss of continuity with the matrix is much easier 
in the case of non-coherent particles than in the 
presence of coherent precipitations. The tendency 
for intergranular crack growth is an effect of planar 
slip band development results from the repeated 
shearing of precipitates by dislocation motion [28]. 
a)              b) 
c)              d) 
Fig. 16.  Subsurface wear morphology of the samples in the T6 state;  
a) and b) perpendicular, and c) and d) and parallel to the sliding direction; Light microscopy, etched with 10 % HF

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502 Lac ho wicz,	M.M.	−	Leśnie wski,	T .	−	Lac ho wicz,	M.B.
In the T6 state, which is formed mainly by coherent 
precipitations [4] and [29], changes typical for surface 
scratching and micro-ploughing were observed (Figs. 
16 and 17). Although changes in the direction of the 
features that formed on the surface of the samples were 
observed, the greatest changes in the cross-section 
occurred in the direction perpendicular to the sliding 
(Figs. 16a and b). The nature of the subsurface wear 
morphology observed in the RRA state was similar to 
those in the T6 state (Fig. 20). Regardless of the heat 
treatment states, microstructure evolution caused by 
plastic deformation was not observed. Small effects 
of plastic deformation were observed in the places 
where the abrasive was pressed into the surface of the 
samples, which led to the formation of characteristic 
tear-shaped cavities (Figs. 16d and 19b). In all the 
samples, it was also observed that the presence of the 
α-AlFeMnSi particles in the subsurface area leads to 
a)               b)
Fig. 17.  Subsurface wear morphology of the samples in the T6 state;  
a) parallel to the sliding direction, and b) perpendicular to the sliding direction, SEM, etched with 10 % HF
a)               b) 
c)                d) 
Fig. 18.  Subsurface wear morphology of the samples after double-stage aging (DA state);  
a) and b) perpendicular, and c) and d) parallel to the sliding direction; Light microscopy, etched with 10 % HF

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503 Effect of Dual-stage Ageing and RRA Treatment on the Three-body Abrasive Wear of the AW7075 Alloy 
its defragmentation and crushing. This also promotes 
its penetration into the friction area (Figs. 16b and c, 
17, 18a, and 20).
The microhardness measurements are 
consistent with the macrohardness measurements. 
The microhardness can be ranked in the following 
increasing order: DA <T6 <RRA. Two effects can 
be expected as a result of the friction: an increase 
in hardness in the near-surface area, which would 
indicate the occurrence of hardening caused by 
plastic deformation; and the fact that increasing the 
temperature during friction may result in a partial 
disappearance and growth of the precipitation 
strengthening phases. The performed studies indicate 
that none of these effects occurred. The hardness 
fluctuated due to the microstructural heterogeneity. 
However, no tendency to increase or decrease the 
hardness directly at the surface was observed. The 
results are shown in Fig. 21. The dashed lines are 
a)              b) 
Fig. 19.  Subsurface wear morphology of the samples in the DA state; parallel to the sliding direction, SEM, etched with 10 % HF
a)              b) 
c)               d) 
Fig. 20.  Subsurface wear morphology of the samples after RRA treatment (RRA state);  
a) and b) perpendicular,  and c) and d) parallel to the sliding direction; light microscopy, etched with 10 % HF

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)7-8, 493-505
504 Lac ho wicz,	M.M.	−	Leśnie wski,	T .	−	Lac ho wicz,	M.B.
responsible for the actual hardness distributions, while 
the solid line is an approximation.
3  CONCLUSIONS
The results of the hardness measurement and 
microscopic examinations, and the underlying reasons 
for the observed behaviour, can be summarized as 
follows:
1. The hardness of the AW7075 alloy is not the only 
determinant of abrasive wear. The conducted 
research shows that the microstructure of the 
tested alloy and the related heat treatment state 
also play an important role in this respect. The 
factor that favours the high value of the K
b
 
coefficient is its high hardness, which is caused 
by the presence of phases that are coherent 
with the matrix. This parameter increases in the 
following order: DA <RRA <T6.
2. The analyses of the wear paths showed the same 
type of damage in all the tested alloy states. 
The scratches, grooves, microcracks, and slight 
features of plastic deformation can be observed 
on the wear surface. The main wear mechanisms 
are therefore controlled by wedge formation and 
micro-ploughing. The delamination tendency may 
also have contributed to the increased wear of the 
DA condition, as delamination was observed in 
this condition. This is most likely related to the 
fact that this state has the lowest hardness.
3. The incoherent precipitation can increase 
hardness, as well as the wear rate, by disturbing 
the plastic flow during particle impact. Larger 
particles can also act as an abrasive and increase 
the wear rate during abrasion. Observations on 
the perpendicular cross-section of the samples 
showed that decohesion developed mainly around 
the grain boundaries and interfacial boundaries. 
The loss of continuity with the matrix is much 
easier in their case than in the presence of 
coherent particles.
4. The presence of large precipitates of the primary 
phases, which do not dissolve at the stage 
of heat treatment, favours their crushing and 
defragmentation during abrasive wear. This 
promotes their penetration into the friction area.
5. No tendency of an increase or decrease of the 
hardness directly at the surface was observed. An 
increase in hardness in the near-surface area could 
be expected, which would indicate the occurrence 
of hardening due to plastic deformation. 
However, an increase in temperature during wear 
could cause a partial disappearance and growth 
of the precipitation strengthening phases, which 
would result in a decrease in surface hardness. 
The studies performed indicate that none of these 
effects occurred.
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