materials Article
Evaluation of the Functional Performance in Turned Workpieces: Methodology and Application to UNS A92024-T3 Álvaro Gómez-Parra 1, * 1 2
*
ID
, Alfredo Sanz 2 and Antonio J. Gámez 1
ID
Department of Mechanical Engineering and Industrial Design, Faculty of Engineering, University of Cadiz, Avenida de la Universidad de Cadiz, 10, Puerto Real, E-11519 Cadiz, Spain;
[email protected] Department of Aerospace Materials and Manufacturing, Polytechnic University of Madrid, Plaza del Cardenal Cisneros, 3, E-28040 Madrid, Spain;
[email protected] Correspondence:
[email protected]; Tel.: +34-956-483-493
Received: 29 June 2018; Accepted: 20 July 2018; Published: 24 July 2018
Abstract: Turning of light alloys as aluminum-based UNS A92024-T3 is broadly implemented in the manufacture of critical aircraft parts, so ensuring a good functional performance of these pieces is essential. Moreover, operational conditions of these pieces include saline environments where corrosion processes are present. In this paper, a methodology for the evaluation of the functional performance in turned pieces is proposed. Specimens affected and not affected by corrosion are compared. In addition, performance in service through tensile stress tests of these parts is considered. The results show that turning improves the functional performance of UNS A92024-T3 alloy and that corrosion can enhance the mechanical properties of this alloy. Keywords: turning; UNS A92024-T3; corrosion; surface integrity; Ra; residual stress; functional performance; ultimate tensile strength
1. Introduction The evaluation of the performance of a manufacturing process is a complex task that can be better approached when four fundamental and complementary points of view are recognized: economical, energetic, environmental, and functional. In this context, the global process performance has been defined as the center of gravity of a tetrahedron defined by setting these four elements in its apexes [1]. In particular, the aeronautical industry considers high-performance manufacturing, even at the cost of a loss in economic performance, provided the process is enhanced from the energetic, environmental and especially, functional points of view [2–4]. Functionality can be understood as the state of health of the workpiece [5]. Therefore, the workpiece functionality is described as its ability to meet quality standards in order to fulfill the required performance in service. For example, the critical components of an aircraft must be manufactured under high specifications of dimensional accuracy, surface finishing, and mechanical properties. In particular, the turning of aluminum alloy pieces by removing cutting fluids increases its environmental performance. This implies a loss of surface integrity that compromises safety and therefore functionality [1,6–8], as dry turning is a very aggressive process that enables tool wear or more specifically, secondary adhesion. This kind of wear involves the addition of machined material to the edge and to the rake face of the tool, giving rise to the so-called built-up edge (BUE) and built-up layer (BUL), respectively [9]. Additionally, functional properties of manufactured elements can be changed by the action of its environment. This action can be more or less intense depending on the surface state of the manufactured element. Therefore, in the case of saline environments, corrosion depends on the surface
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finishing of the worked elements [10] and, consequently, on the manufacturing process. In these cases, manufactured element. Therefore, in the case of saline environments, corrosion depends on the the influence of the corrosion damage on the surface properties of the workpieces must be taken surface finishing of the worked elements [10] and, consequently, on the manufacturing process. In into account [11]. This is the case of different structural elements of aircrafts, especially transoceanic these cases, the influence of the corrosion damage on the surface properties of the workpieces must ones.beAll considered, in order approach conditions of the actualelements service, it necessary to research taken into account [11]. to This is the case of different structural of isaircrafts, especially the influence of manufacturing process on mechanicals properties in conjunction with a corrosion transoceanic ones. All considered, in order to approach conditions of the actual service, it is necessary environment. to our knowledge, there areon nomechanicals studies in the currentinliterature that consider to researchHowever, the influence of manufacturing process properties conjunction with a the salinity effect and its relationship the machining process and the functional performance of corrosion environment. However, to with our knowledge, there are no studies in the current literature that consider the salinity effect and its relationship with the machining process and the functional the workpiece. For this reason, this paper analyses the influence of turning processes in the surface performance of the workpiece. this reason, thiscorrosion paper analyses the influence of turning processes integrity of UNS A92024-T3 alloys,For before and after by a saline atmosphere. More specifically, in the surface integrity of UNS A92024-T3 alloys, before and after corrosion by a saline atmosphere. the ultimate tensile strength (UTS) is measured as a reference parameter to assess the functional More specifically, the ultimate tensile strength (UTS) is measured as a reference parameter to assess performance of the material under corrosion. the functional performance of the material under corrosion.
2. Materials and Methods
2. Materials and Methods
An experimental methodology was designed to achieve the proposed goal (Figure 1). An experimental methodology was designed to achieve the proposed goal (Figure 1).
Figure 1. Experimental methodology scheme.
Figure 1. Experimental methodology scheme.
Al-Cu alloy UNS A92024-T3 specimens (composition in Table 1 [12]) were machined using a CNC Eclipse Alecopspecimens (Mondragón, Spain) (Figure Specimens were machined designed according Al-Culathe alloy UNS from A92024-T3 (composition in 1). Table 1 [12]) were using a CNC to ISO 6892-1:2016 (Figure 2a) [13]. The entire machining process was performed in absence of cooling lathe Eclipse from Alecop (Mondragón, Spain) (Figure 1). Specimens were designed according to ISO fluids, therefore improving environmental performances.
6892-1:2016 (Figure 2a) [13]. The entire machining process was performed in absence of cooling fluids, therefore improvingTable environmental performances. 1. Composition of aluminum-copper alloy UNS A92024 (% weight). Cu Mg Mnof aluminum-copper Si Fe Zn Ti A92024 Cr (% weight). Al Table 1. Composition alloy UNS 4.0 1.5 0.6 0.5 0.5 0.25 0.15 0.10 Rest Cu
Mg
Mn
Si
Fe
Zn
Ti
Cr
Al
4.0
1.5
0.6
0.5
0.5
0.25
0.15
0.10
Rest
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Blocks of 32 specimens—divided in two equal sets of 16 pieces—were dry machined for this study. Workpieces forofSet were only dry turned before being tested, whiledry samples for Set were Blocks 32 Ispecimens—divided in two equal setstensile of 16 pieces—were machined forIIthis exposed corrosion for after turned and before study. to Workpieces Setbeing I weredry only dry turned beforebeing beingtensile tensile tested. tested, while samples for Set II Machining all specimens involved roughing process a cutting speed (Vc) of were exposed procedure to corrosionofafter being dry turned anda before being tensileusing tested. 80 m/min, a feed rate (f ) of 0.03 mm/min and a cutting depth (d) of 0.50 mm cuttingspeed parameters. Machining procedure of all specimens involved a roughing process using as a cutting (Vc) 80 m/min,pass a feed ratesample (f) of 0.03 mm/min andcarried a cutting (d)conditions of 0.50 mmand as cutting Theoffinishing of the surfaces were outdepth in dry using aparameters. new tool for The finishing specimen pass of thewith sample carriedshown out in dry conditions and using a new tool for each machined thesurfaces cutting were parameters in Table 2. each machined specimen with the cutting parameters shown in Table 2. The cutting tools used were neutral interchangeable insert (WC-Co) with commercial reference The DCMT cutting 070208-F2 tools used HX were(Seco neutral interchangeable (WC-Co) with commercial reference SECO, ref. Tools AB, Fagersta,insert Sweden). SECO, ref. DCMT 070208-F2 HXof(Seco Tools AB, Fagersta, Sweden). The surface microgeometry the samples was evaluated through the average surface roughness The surface microgeometry of the samples was evaluated through average surface roughness parameter (Ra) according to the standard ISO 4288:1996 [14]. Four the profiles were acquired in four parameter (Ra) according to the standard ISO 4288:1996 [14]. Four profiles were acquired inGmbH, four equidistant generatrices for each sample using a Mahr Perthometer M1 profilometer (Mahr equidistant generatrices for each sample using a Mahr Perthometer M1 profilometer (Mahr GmbH, Göttingen, Germany). Each specimen Ra was calculated as the mean value of the four Ra of the Göttingen, Germany). Each specimen Ra was calculated as the mean value of the four Ra of the measured profiles. measured profiles. Table 2. Cutting parameters performed in machining test for a total of 16 experiments. Table 2. Cutting parameters performed in machining test for a total of 16 experiments. Vc (m/min) Vc (m/min) 40 40 60 60 80 80 100 100
(mm/r) ff (mm/r) 0.02 0.02 0.05 0.05 0.10 0.10 0.20 0.20
d (mm) d (mm) 0.500.50 0.500.50 0.500.50 0.500.50
Next,Set Set II II was to corrosion by immersion in a 10-L distilledof anddistilled deionized Next, wasexposed exposed to corrosion by immersion in solution a 10-L of solution and water and NaCl (3.5%) for 72 h at 296.15 K (Figure 2b) following standard ASTM NACE/ASTMG31deionized water and NaCl (3.5%) for 72 h at 296.15 K (Figure 2b) following standard ASTM 12a [15]. Water evaporation was controlled every day. NACE/ASTMG31-12a [15]. Water evaporation was controlled every day. After each corrosive treatment, the workpieces were cleaned with distilled water a similar After each corrosive treatment, the workpieces were cleaned with distilled water in in a similar way way to overseas aircrafts. to overseas aircrafts. Finally, in order to obtain the UTS, both sets underwent a tensile test with a Shimadzu Finally, in order to obtain the UTS, both sets underwent a tensile test with a Shimadzu Autograph Autograph AG-X (50 kN) tensile-compression machine (Shimadzu, Kyoto, Japan) for a precision AG-X (50 kN) tensile-compression machine (Shimadzu, Kyoto, Japan) for a precision within 1%. within 1%. The crosshead velocity was u = 14.5 mm/min for all tests and the standard ISO 6892-1:2016 The crosshead velocity was u = 14.5 mm/min for all tests and the standard ISO 6892-1:2016 was used. was used.
(a)
(b)
Figure 2. (a) Specimen dimensions according to standard UNE-EN ISO 6892-1:2016. (b) Set II samples Figure 2. (a) Specimen dimensions according to standard UNE-EN ISO 6892-1:2016. (b) Set II samples during a corrosion test by immersion. during a corrosion test by immersion.
On the other hand, residual stress measurements were carried out by blind hole drilling, On the the other hand, residual stress[16], measurements carriedfrom outVishay by blind hole North drilling, following ASTM E837-13a standard using a RS-200were equipment (Raleigh, following the ASTM E837-13a standard [16],purpose, using a RS-200 equipment from Vishay (Raleigh, North Carolina, USA) (Figure 3) [17,18]. For this CEA-13-062UM strain gages (Vishay Precision Carolina, USA) (Figure 3) [17,18].Raleigh, For thisNC, purpose, strain gages (Vishay Precision Group—Micro-Measurements, USA) CEA-13-062UM were used in this study. This method was conducted on bigger specimens with aNC, radius of 50 mmused as demonstrator, blind hole drilling is not Group—Micro-Measurements, Raleigh, USA) were in this study. as This method was conducted
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suitable for the 3.81 mm radii of curvature specimens. These samples followed the same turning and corrosion procedures as the original set of 32 specimens for reproducibility. on bigger specimens with a radius of 50 mm as demonstrator, as blind hole drilling is not suitable for Because residual stress in machined workpieces varies with depth from the specimen surface, thethe 3.81 mm radii of curvature specimens. These samples followed the same turning and corrosion integral method was used to transform strains into stresses. Measurements had a probability procedures as the original set of 32 specimens for reproducibility. bound of 90%.
(a)
(b)
(c)
Figure 3. (a) Residual stress measurement of noncorroded specimen. (b) Specimen corroded after 72 Figure 3. (a) Residual stress measurement of noncorroded specimen. (b) Specimen corroded h in solution of distilled and deionized water and NaCl (3.5%). (c) Set up of measures in corroded after 72 h in solution of distilled and deionized water and NaCl (3.5%). (c) Set up of measures in specimen. corroded specimen.
3. Results and Discussion Because residual stress in machined workpieces varies with depth from the specimen surface, As the time of machining is very short—ranging from 8.51 s for the shortest combination of the integral method was used to transform strains into stresses. Measurements had a probability cutting speed and feed rate to 212.74 s for the largest—no microstructural changes on the tool were bound of 90%. expected [9,19–21]. However, the temperature can be high enough for softening the Al matrix and developing primary BUL. Figure 4 shows Stereoscopic Optical Microscopy (SOM) images of tools 3. Results and Discussion after machining under two different cutting parameters and a scheme of tool wear by secondary As the time of machining is very short—ranging from 8.51 s for the shortest combination of adhesion. was developed the rake face the tool andmicrostructural its size was bigger when on cutting speed cuttingBUL speed and feed rateonto to 212.74 s for theoflargest—no changes the tool were increased (Figure 4a,c). Primary BUL was formedcan in the to 10 s offor machining, and wasmatrix formedand expected [9,19–21]. However, the temperature be first high5enough softening theit Al by pure aluminum (Figure 4e 4(1)) [9]. Stereoscopic Tool changesOptical facilitated the mechanical adhesion of the developing primary BUL. Figure shows Microscopy (SOM) images of tools after machined alloy, giving rise to BUE (Figure 4b,d). BUE was formed by the alloy material and it grew machining under two different cutting parameters and a scheme of tool wear by secondary adhesion. to aBUL critical (Figure 4eonto (2)) the [1,9].rake When theoftemperature high, BUE wassize developed face the tool andwas its sufficiently size was bigger whensoftened cuttingand speed extruded onto the rake face, giving rise to a secondary BUL (Figure 4e (3)) [1,9]. The temperature in increased (Figure 4a,c). Primary BUL was formed in the first 5 to 10 s of machining, and it was formed the cutting region was higher for increasing cutting speeds [7]. This explains the aforementioned BUL by pure aluminum (Figure 4e (1)) [9]. Tool changes facilitated the mechanical adhesion of the machined thickness. According to that, a lower BUE thickness was detected when lower cutting speed was alloy, giving rise to BUE (Figure 4b,d). BUE was formed by the alloy material and it grew to a critical applied. On the other hand, a higher feed involved a higher lateral chip compression, facilitating BUL size (Figure 4e (2)) [1,9]. When the temperature was sufficiently high, BUE softened and extruded through the increase of temperature caused by the relaxation process after deformation [22]. onto the rake face, giving rise to a secondary BUL (Figure 4e (3)) [1,9]. The temperature in the cutting region was higher for increasing cutting speeds [7]. This explains the aforementioned BUL thickness. According to that, a lower BUE thickness was detected when lower cutting speed was applied. On the other hand, a higher feed involved a higher lateral chip compression, facilitating BUL through the increase of temperature caused by the relaxation process after deformation [22].
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1 mm
1 mm
(b)
(a) 1 mm
1 mm
(d)
(c)
(e) Figure 4. Comparison of built-up layer (BUL) and built-up edge (BUE) for different cases. (a,b) Vc = Figure 4. Comparison of built-up layer (BUL) and built-up edge (BUE) for different cases. (a,b) Vc = 100 100 m/min, f = 0.2 mm/r. (c,d) Vc = 40 m/min, f = 0.05 mm/r. (e) Scheme of the BUL and BUE formation. m/min, f = 0.2 mm/r. (c,d) Vc = 40 m/min, f = 0.05 mm/r. (e) Scheme of the BUL and BUE formation.
From geometric considerations, Ra depends directly on f and the edge position angle of the tool From geometric considerations, Ra depends directly on f and thediminished edge position angle of the tool for horizontal turning processes [1,9]. The BUE development this angle and, for horizontal turning processes [1,9]. The BUE development diminished this angle and, consequently, consequently, the height of the peaks in the profile reduced and smoothened, thereby decreasing Ra the height of the peaksthat in the profileofreduced thereby decreasing Ra (Figure (Figure 5a). This shows the effect the tool and wearsmoothened, seems to be responsible for a decrease in Ra 5a). in This shows that the effect of the tool wear seems to be responsible for a decrease in Ra in certain sets certain sets of parameters. Secondary adhesion is a dynamic process, that is to say, the morphologyof a dynamic process, that when is to say, thewas morphology tool can ofparameters. the tool canSecondary change at adhesion any time is (Figure 5a). In this sense, BUE extruded, of thethe height of change at any time 5a). In this5b) sense, peaks increased and (Figure so did Ra (Figure [1,9].when BUE was extruded, the height of peaks increased and so did Ra (Figure 5b) [1,9].
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Figure 5. Effect of tool wear by secondary adhesion in the workpiece roughness profile for a
Figure 5. ofoftool wear by secondary adhesion in the in workpiece roughness profile forprofile a horizontal Figure 5. Effect Effectdry tool wear by secondary adhesion the workpiece roughness for a horizontal turning process. dry turning process. horizontal dry turning process. According to this, the extreme value of Ra found in (Vc, f) = (60, 0.05) can be explained (Figure 6). On the other hand, dryvalue turning shortening the life, it be may have a positive According to this, this, thedespite extreme value Rafound foundinin (Vc,f )f)==(60, (60,tool 0.05) can be explained (Figure According to the extreme ofofsignificantly Ra (Vc, 0.05) can explained (Figure 6). effect on the microgeometrical properties of the specimen, at least in a controlled length of machining 6). other hand, despite turning significantly shortening the life, toolitlife, it have may have a positive OnOn thethe other hand, despite drydry turning significantly shortening the tool may a positive effect [23]. In fact, surface integrity got worse as feed increased for every tested cutting speed, as expected effect the microgeometrical properties the specimen, at least in a controlled length of machining on theon microgeometrical properties of theofspecimen, at least in a controlled length of machining [23]. (Figure 6). These results are in good agreement with previous studies [19,24].
[23]. In fact, surface integrity worse feed increased forevery everytested testedcutting cutting speed, speed, as as expected In fact, surface integrity gotgot worse as as feed increased for expected (Figure studies [19,24]. [19,24]. (Figure 6). 6). These These results results are are in in good good agreement agreement with with previous previous studies
Figure 6. Evolution of Ra/f for all the cutting speeds studied. Error bars show the statistical standard deviation.
Figure 6.6.Evolution Evolution of Ra/f forthe allcutting the cutting studied. Error bars the statistical Figure of Ra/f for all speedsspeeds studied. Error bars show theshow statistical standard standard deviation. deviation.
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Figure Figure 77 shows shows how how the the UTS UTS increased increased with with the the feed feed rate rate for for each each tested testedspecimen. specimen.
Figure 7. 7. Changes in UTS/f UTS/f for analyzed cutting cutting speeds. speeds. Set I, noncorroded noncorroded specimens specimens Figure Changes in for all all the the analyzed Set I, (continuous lines). lines). Set Set II, II, corroded corroded specimens specimens (dotted (dotted lines). lines). (continuous
We can observe that the machining process enhanced the tensile strength for all the studied We can observe that the machining process enhanced the tensile strength for all the studied cases.2 cases. In fact, the standardized value of UTS for UNS A92024-T3 lies between 440 and 450 N/mm In fact, the standardized value of UTS for UNS A92024-T3 lies between 440 and 450 N/mm2 [12,25,26]. [12,25,26]. Although the UTS variation is less than 4% of the reference value for this alloy, it is worth Although the UTS variation is less than 4% of the reference value for this alloy, it is worth noting that the noting that the best results are achieved for higher feed conditions. Our findings show that higher Ra best results are achieved for higher feed conditions. Our findings show that higher Ra results in higher results in higher UTS. This can suggest that physicochemical properties of the material prevail over UTS. This can suggest that physicochemical properties of the material prevail over microgeometrical microgeometrical properties for surface integrity functional performance [27–29]. properties for surface integrity functional performance [27–29]. As expected, higher feed rates resulted in higher compressive stresses in the surface of the As expected, higher feed rates resulted in higher compressive stresses in the surface of the specimens (Figure 8) [29–32]. However, the stress distribution was not homogeneous. The region specimens (Figure 8) [29–32]. However, the stress distribution was not homogeneous. The region between 0.1 to 0.9 mm was under compression, while tensile stresses were located in the first 0.1 mm between 0.1 to 0.9 mm was under compression, while tensile stresses were located in the first 0.1 mm of the surface where the corrosion process took place. In fact, corrosion of Al-Cu alloys in aerated of the surface where the corrosion process took place. In fact, corrosion of Al-Cu alloys in aerated NaCl solutions is complex. As a first step, the Cu of anodic intermetallics is dissolved, changing their NaCl solutions is complex. As a first step, the Cu of anodic intermetallics is dissolved, changing their character to a cathodic behavior. The rest of intermetallics are cathodic to the Al matrix and therefore character to a cathodic behavior. The rest of intermetallics are cathodic to the Al matrix and therefore OH− is produced in the surrounding of those intermetallics. As a result, the metal matrix is dissolved OH− is produced in the surrounding of those intermetallics. As a result, the metal matrix is dissolved by alkaline action, provoking them to fall. This process is known as Localized Alkaline Corrosion by alkaline action, provoking them to fall. This process is known as Localized Alkaline Corrosion (LAC), and it does not promote the presence of cracks onto the alloy surface [11,33]. At macroscopic (LAC), and it does not promote the presence of cracks onto the alloy surface [11,33]. At macroscopic scale, a preferential attack cannot be seen. Moreover, different mechanisms are responsible for the scale, a preferential attack cannot be seen. Moreover, different mechanisms are responsible for the deterioration [33], although the final results are homogeneously distributed onto the surface. deterioration [33], although the final results are homogeneously distributed onto the surface. Therefore, Therefore, no pitting is developed on the specimen surfaces (Figure 9). For this reason, corrosion only no pitting is developed on the specimen surfaces (Figure 9). For this reason, corrosion only affects affects the first layers of material, removing the tensile stress region and therefore enhancing the the first layers of material, removing the tensile stress region and therefore enhancing the functional functional performance by a significant increase in the UTS for each workpiece, (Figure 7). performance by a significant increase in the UTS for each workpiece, (Figure 7). Figure 8 shows the behavior of the axial residual stress with depth in the material surface. Axial residual stresses must be taken into account because they contribute to the stress carried out by the tensile tests. Furthermore, microgeometrical defects are disposed perpendicularly to the tensile
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Figure 8 shows the behavior of the axial residual stress with depth in the material surface. 8 of 8 of 11 11 Axial residual stresses must be taken into account because they contribute to the stress carried out bystrength, the tensile tests. Furthermore, microgeometrical defects aredefects, disposed perpendicularly to the any compressive stress willtend tend close surface defects,improving improving functional strength, soso any compressive stress will to toclose surface thethe functional tensile strength, so any compressive stress will tend to close surface defects, improving the functional performance [29,34]. addition, level compressive residual stress increases with feed performance [29,34]. InIn addition, thethe level of of compressive residual stress increases with feed forfor performance [29,34]. In addition, the level of compressive residual stress increases with feed for noncorroded specimens, strengthening the compressive residual stress that the unmachined material noncorroded specimens, strengthening the compressive residual stress that the unmachined material noncorroded specimens, strengthening the compressive residual stress thatresidual the unmachined material originally supports [30–32]. contrast, decreasing feeds, compressive residual stresses are lower originally supports [30–32]. ByBy contrast, forfor decreasing feeds, compressive stresses are lower originally supports [30–32]. By contrast, for decreasing feeds, compressive residual stresses are than that unmachined specimens. This say, functional performance improved higher than that of of thethe unmachined specimens. This is is to to say, functional performance is is improved at at higher lower than that of the unmachined specimens. This is to say, functional performance is improved at feeds. feeds. higher feeds. Materials 2018, x FOR PEER REVIEW Materials 2018, 11,11, x FOR PEER REVIEW
(b)(b)
(a)(a)
Figure Evolution 8. Evolution of axial residual stress/depth after machining for the cutting parameters indicated Figure Figure8. 8. Evolutionof ofaxial axialresidual residual stress/depth stress/depthafter aftermachining machiningfor forthe thecutting cuttingparameters parametersindicated indicated in noncorroded and corroded specimens. (a) Vc = 80 mm/min, (b) Vc = 100 mm/min. Two feed rates in specimens. (a) (a) Vc Vc = = 80 80 mm/min, mm/min, (b) in noncorroded noncorroded and and corroded corroded specimens. (b) Vc Vc == 100 100 mm/min. mm/min.Two Twofeed feed rates rates shown in both cases, f = 0.02 mm/r and f = 0.2 mm/r. shown mm/r. shown in in both both cases, cases, ff ==0.02 0.02mm/r mm/rand andf =f 0.2 = 0.2 mm/r.
summary,corrosion corrosionremoved removedthethetensile tensilestress stressregion regionat atthethesurface surfaceof ofthetheworkpieces, workpieces, InInsummary, In summary, corrosionperformance. removed theHowever, tensile stress region at the surface of the workpieces, improving the functional an accurate control of the corrosion process improving the functional performance. However, an accurate control of the corrosion process is is improving the functional performance. However, an accurate control of the corrosion process is needed because corrosive process can have impact intermetallic loss, these particles needed because thethe corrosive process can have anan impact in in thethe intermetallic loss, these particles needed because the corrosive process can have an impact in the intermetallic loss, these particles being being responsible alloy strength [33]. being responsible forfor thethe alloy strength [33]. responsible for the alloy strength [33].
(a)(a)
(b)(b)
Figure (a) 9. (a) General image of corroded specimen (Vc = 60 m/min, = 0.2 mm/r). Detail (×72) of the Figure f =ff0.2 mm/r). (b)(b) Detail (×72) Figure 9. 9. (a)General Generalimage imageof ofcorroded corrodedspecimen specimen(Vc (Vc==60 60m/min, m/min, = 0.2 mm/r). (b) Detail (×of 72)the of corroded surface. corroded surface. the corroded surface.
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4. Conclusions A novel approach to study the influence of turning processes in the UTS performance after corrosion of the UNS A92024-T3 alloy has been carried out. From analysis of the results, the conclusions can be summarized as follows: 1.
2.
3.
4.
Machining process can improve the tensile strength of horizontal dry turned samples of aeronautical alloy UNS A92024-T3. In this limited context, functional performance is favored by machining. Physicochemical properties are responsible for improving the mechanical properties and hence the functional performance. Generally speaking, the UTS increases with the feed. Thus, there is no predominant influence of the microgeometrical properties acquired after machining over the UTS. In this sense, tensile residual stress taking place on the surface after machining is not large enough to generate a decrease of UTS value. The compressive residual stress after machining is responsible for the best results of UTS. Furthermore, as the feed increases, the compressive residual stress increases too, thereby improving the value of compressive residual stress of the unmachined material. Thus, the higher the compressive residual stress, the higher the UTS value. The results of the test of tensile stress after corrosion show a generalized improvement of the UTS value. The corrosion process removes the first layers of material. These layers, as shown in the results, carry a tensile residual stress and are softer than the unmachined material.
Author Contributions: Á.G.-P. and A.S. designed the methodology. Á.G.-P. performed the experiments. A.J.G. and Á.G.-P. discussed the results and wrote the manuscript. Funding: This work has been funded by the University of Cadiz: Program for development and promotion of research and transfer activities. Acknowledgments: In memoriam of Mariano Marcos. Conflicts of Interest: The authors declare no conflict of interest.
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