micromachines Article
Effects of Process Conditions on the Mechanical Behavior of Aluminium Wrought Alloy EN AW-2219 (AlCu6Mn) Additively Manufactured by Laser Beam Melting in Powder Bed Michael Cornelius Hermann Karg 1,2,3, *, Bhrigu Ahuja 1,2,3 , Sebastian Wiesenmayer 1 , Sergey Vyacheslavovich Kuryntsev 4 and Michael Schmidt 1,2,3 1
2 3 4
*
Institute of Photonic Technologies (LPT), Friedrich-Alexander-Universität Erlangen-Nürnberg FAU, Konrad-Zuse-Straße 3/5, 91052 Erlangen, Germany;
[email protected] (B.A.);
[email protected] (S.W.);
[email protected] (M.S.) Collaborative Research Center 814—Additive Manufacturing (CRC 814), Am Weichselgarten 9, 91058 Erlangen-Tennenlohe, Germany Erlangen Graduate School in Advanced Optical Technologies (SAOT), Paul-Gordan-Straße 6, 91052 Erlangen, Germany Department of Laser Technologies, Kazan National Research Technical University, K. Marx Str. 10, 420111 Kazan, Russia;
[email protected] Correspondence:
[email protected]; Tel.: +49-9131-85-64101
Academic Editor: Maria Farsari Received: 22 November 2016; Accepted: 11 January 2017; Published: 16 January 2017
Abstract: Additive manufacturing is especially suitable for complex-shaped 3D parts with integrated and optimized functionality realized by filigree geometries. Such designs benefit from low safety factors in mechanical layout. This demands ductile materials that reduce stress peaks by predictable plastic deformation instead of failure. Al–Cu wrought alloys are established materials meeting this requirement. Additionally, they provide high specific strengths. As the designation “Wrought Alloys” implies, they are intended for manufacturing by hot or cold working. When cast or welded, they are prone to solidification cracks. Al–Si fillers can alleviate this, but impair ductility. Being closely related to welding, Laser Beam Melting in Powder Bed (LBM) of Al–Cu wrought alloys like EN AW-2219 can be considered challenging. In LBM of aluminium alloys, only easily-weldable Al–Si casting alloys have succeeded commercially today. This article discusses the influences of boundary conditions during LBM of EN AW-2219 on sample porosity and tensile test results, supported by metallographic microsections and fractography. Load direction was varied relative to LBM build-up direction. T6 heat treatment was applied to half of the samples. Pronounced anisotropy was observed. Remarkably, elongation at break of T6 specimens loaded along the build-up direction exceeded the values from literature for conventionally manufactured EN AW-2219 by a factor of two. Keywords: additive manufacturing; 3D printing; powder bed fusion; aluminium copper wrought alloy EN AW-2219; AlCu6Mn; tensile test; Selective Laser Melting™
1. Introduction 1.1. Terminology of Additive Manufacturing Technology This paper is dedicated to additive manufacturing from a metal powder bed without binder using a laser beam. ISO/ASTM F52900 and ISO 17296 define a higher-level category “powder bed fusion” including other technologies that employ incoherent radiation, laser or electron beams to process polymers, ceramics or metals with or without binder [1,2]. In this paper, the precise technology Micromachines 2017, 8, 23; doi:10.3390/mi8010023
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process polymers, ceramics or metals with or without binder [1,2]. In this paper, the precise of interest isofreferred as Laserto Beam Melting PowderinBed (LBM) in (LBM) the style of VDI [3]. technology interest to is referred as Laser BeaminMelting Powder Bed in the style3405 of VDI Figure 1a shows the machine principle and Figure 1b the process variables. An established trademark 3405 [3]. Figure 1a shows the machine principle and Figure 1b the process variables. An established for LBM (among others) is, for example, Laser Melting™ [4].(SLM™) [4]. trademark for LBM (among others) is, forSelective example, Selective Laser(SLM™) Melting™
Figure Figure 1. 1. (a) (a) Basic Basic machine machine setup setup of of Laser Laser Beam Beam Melting Melting in in Powder Powder Bed Bed (LBM); (LBM); (b) (b) 3D 3D build-up build-up from from overlapping weld tracks. overlapping weld tracks.
1.2. of Aluminium Aluminium Alloys Alloys 1.2. Terminology Terminology of European European Standard Standard EN EN 12258-1 12258-1 defines defines an an Al Al wrought wrought alloy alloy as as an an “alloy “alloy primarily primarily intended intended for for the production of wrought products by hot and/or cold working” and likewise for casting the production of wrought products by hot and/or cold working” and likewise for castingalloys alloys[5]. [5]. AW stands for for “aluminium “aluminium wrought” wrought” in in alloy alloy designations designations [6]. [6]. Alloys AW stands Alloys are are defined defined by by chemical chemical compositions [7–9].“Wrought” “Wrought” and “casting” are of part of Aldesignations. alloy designations. In this paper, compositions [7–9]. and “casting” are part Al alloy In this paper, processing processing is stated as either by LBM or conventionally; the latter meaning by working or casting, is stated as either by LBM or conventionally; the latter meaning by working or casting, depending on depending on the alloy. the Table 1 shows the EN AW-2219 used for LBM experiments. the alloy. Table 1 shows composition ofcomposition EN AW-2219ofused for LBM experiments. Table Table1.1.Composition CompositionofofEN ENAW-2219 AW-2219according accordingtoto[7] [7]ininwt wt%; %;single singlenumbers numbersmean meanupper upperlimits. limits.
Cu Mn 5.8–6.8 Mn 0.2–0.4
Cu
5.8–6.8
0.2–0.4
Ti Ti 0.02–0.1
0.02–0.1
V Zr Zn Mg 0.05–0.15 Zr0.1–0.25Zn 0.1 Mg 0.02
V
0.05–0.15
0.1–0.25
0.1
0.02
Si Fe Al 0.2Si 0.3 Fe balance Al 0.2
0.3
balance
1.3. Motivation 1.3. Motivation Industrial use of and research on LBM have increased rapidly in recent years [4], but the Industrial use ofisand LBM shows have increased rapidly infor recent years [4], but the material material spectrum stillresearch limited.onLBM great potential functionally optimized and spectrum is still limited. LBM shows great potential for functionally optimized and light-weight light-weight designs. For such applications, conventionally manufactured Al wrought alloys are designs. Fordue suchtoapplications, conventionally manufactured wrought alloys areadjustable establishedby due to established high strength-to-weight ratios, predictableAlmechanics that are heat high strength-to-weight predictable mechanics that deformation are adjustable by heat treatment and the treatment and the ability ratios, to avoid sudden failure by plastic [10,11]. ability to most avoidcommon sudden failure deformation [10,11]. The Al alloybyinplastic LBM today is AlSi10Mg, among other Al–Si casting alloys [12–15]. The most common Al filler alloy in LBM today is AlSi10Mg, among otheralloys Al–Si [16]. casting alloys [12–15]. AlSi10Mg is also used as material for welding Al–Cu wrought Ultimate tensile strength 320–360 MPa and elongation breakwrought (E) of 2%–8% of LBM AlSi10Mg were AlSi10Mg(UTS) is alsoof used as filler material for weldingat Al–Cu alloys [16]. Ultimate tensile T6 strength reported [13]. According [13], elongation at(E) break is higher orthogonal to the direction (UTS) of 320–360 MPa andtoelongation at break of 2%–8% of LBM AlSi10Mg T6 build-up were reported [13]. than parallel it. elongation This anisotropy wasis not reported in [17]tobased on a round robinthan withparallel machine According to to [13], at break higher orthogonal the build-up direction to manufacturers and academic institutions. Established laser power for LBM of Al alloys is 400 W; it. This anisotropy was not reported in [17] based on a round robin with machine manufacturers and research experimentsEstablished with 1000laser W power have for been published [18]. Al–Mg–Sc alloys have been academic institutions. LBM of Al alloys is 400 W; research experiments with continuously researched in LBM [19–21]. Industrial usebeen might be impeded by high in limited global 1000 W have been published [18]. Al–Mg–Sc alloys have continuously researched LBM [19–21]. annual Sc use production only 10–15 t [22]. LBM of very high Al–Zn alloys encountered Industrial might be of impeded by high limited global annual Sc strength production of only 10–15 t [22]. LBM issues cracking andAl–Zn alloy alloys changes by evaporation [23,24]. EN AW-7075 plus 4 wt % Si was of veryofhigh strength encountered issues of of Zn cracking and alloy changes by evaporation of crack-free LBM with relative rel = 98.9%, butLBM Zn content and tensile test of this Zn [23,24].after EN AW-7075 plus 4 wt %density Si was ρcrack-free after with relative density ρrelresults = 98.9%, but Al–Si–Zn published Loss ofalloy Zn inwere LBMnot of published Al–Zn–Mg–Cu was reported [26] Zn contentalloy and were tensilenot test results of[14,25]. this Al–Si–Zn [14,25]. Loss of Zn ininLBM and micrograph areas mm were but information about cracks, andinformation tensile test of Al–Zn–Mg–Cu was 99.9% [29,30] and results from tensile testing of EN AW-2618A [31] were published by the authors. Others followed Micromachines 2017, 8, 23 3 of 11 to publish on LBM of 2xxx series Al–Cu wrought alloys [32,33]. Micromachines 2017, 8, 23 3 of 11 Conventionally manufactured manufactured EN reaches 414 414 MPa MPa ultimate tensile tensile strength,strength, 10% Conventionally ENAW-2219 AW-2219 reaches ultimate elongation at break andand performs wellwell at elevated temperatures [34]. [34]. 10% elongation at break performs at elevated temperatures Conventionally manufactured EN AW-2219 reaches 414 MPa ultimate tensile strength, 10% Thegoal goalat thisand contribution is to to investigate the properties ENEN AW-2219 The ofof this contribution is investigate the mechanical mechanical propertiesof of AW-2219 elongation break performs well at elevated temperatures [34]. manufactured by LBM under consideration of heat treatment and build orientation relative to to load. The goal of this contribution is to investigate the mechanical properties of EN AW-2219 manufactured by LBM under consideration of heat treatment and build orientation relative load. manufactured by LBM under consideration of heat treatment and build orientation relative to load.
Materialsand andMethods Methods 2. 2. Materials
2. Materials and Methods
2.1. PrealloyedArgon ArgonAtomized AtomizedPowder Powder with with Chemical Chemical Composition 2.1. Prealloyed CompositionofofEN ENAW-2219 AW-2219 2.1. Prealloyed Argon Atomized Powder with Chemical Composition of EN AW-2219
Powder with the chemical compositionofofEN EN AW-2219 shown Table 1 had been atomized Powder with the chemical composition AW-2219 shown in in Table 1 had been atomized with Powder with the chemical composition of EN AW-2219 shown in Table 1 had been atomized with Ar by TLS (TLS Technik GmbH & Co Spezialpulver KG, Bitterfeld-Wolfen, Germany). It was Ar by TLS (TLS Technik GmbH & Co Spezialpulver KG, Bitterfeld-Wolfen, Germany). It was vibration with Arsieved by TLS Technik GmbH &Technologies Co Spezialpulver Bitterfeld-Wolfen, Germany). It was vibration at (TLS Institute of Photonic (LPT,KG, Erlangen, Germany) under Ar sieved at Institute of Photonic Technologies (LPT, Erlangen, Germany) under Ar between 20between and 63 µm vibration sieved at Institute of Photonic Technologies (LPT, Erlangen, Germany) under Ar between 20 and 63 µm mesh width. Scanning electron microscopy (SEM) on a Zeiss Merlin (Carl Zeiss mesh width. Scanning electron microscopy (SEM) on a Zeiss Merlin (Carl Zeiss Microscopy GmbH, 20 and 63GmbH, µm mesh Scanning electron microscopy (SEM) on particles a Zeiss Merlin (Carl Zeiss Microscopy Jena,width. Germany) in Figure 2 shows many remaining
