Development and production of Al-Cu-li wires by powder metallurgy routes and their application in WAAM techniques
- Autores: Paula Rodriguez Gonzalez
- Directores de la Tesis: Elena Gordo Odériz (dir. tes.), Elisa María Ruiz Navas (codir. tes.)
- Lectura: En la Universidad Carlos III de Madrid ( España ) en 2023
- Idioma: inglés
- Tribunal Calificador de la Tesis: Isabel Montealegre Melendez (presid.), Carlos Romero Villarreal (secret.), Laura Córdova González (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de Madrid
- Materias:
- Enlaces
- Tesis en acceso abierto en: e-Archivo
- Resumen
This doctoral thesis with the title "Development and production of Al-Cu-Li wires by powder metallurgy routes and their application in WAAM techniques." has been carried out at the Powder Technology Group (GTP) of the University Carlos III of Madrid (UC3M), in the framework of the PhD programme in Materials Science and Engineering of the UC3M, under the supervision of Dr Elisa María Ruiz Navas and Dr Elena Gordo. This thesis has been developed mainly at UC3M and through a research stay of 4 months and 3 weeks at RHP Technology GmbH located in Seibersdorf, Austria. The work at RHP was carried out under the supervision of Dr Erich Neubauer and Enrique Ariza.
Two articles were published in JCR journals: - Wire Arc Additive Manufacturing (WAAM) for Aluminum-Lithium Alloys: A Review. Authors: P. Rodríguez-González, E.M. Ruiz-Navas, E. Gordo. Journal: Materials, Q1, vol. 16, no. 4, 2023.
- Effect of heat treatment prior to direct hot-extrusion processing of Al¿Cu¿Li alloy. Authors: P. Rodríguez-González, E.M. Ruiz-Navas, E. Gordo. Journal: Metals, Q2, vol. 12, no. 6, 2022. https://doi.org/10.3390/met12061046 And two articles are uploaded to the journal, under review and pending publication.
- Microstructural, chemical, and mechanical characterization of extruded aluminium rods. Authors: P. Rodríguez-González, M.A. Monge, E. Gordo, E.M. Ruiz-Navas. Journal: Materials Characterization.
- Assessment of Plasma Deposition parameters for DED Additive Manufacturing of AA2319. Authors: P. Rodríguez-González, E. Neubauer, E. Ariza, L. Bolzoni, E. Gordo, E.M. Ruiz-Navas. Journal: Materials Science and Engineering A. Submitted to journal.
During this thesis I participated in two competitive projects: - ADITIMAT-CM. Additive Manufacturing: from material to application. S2018/NMT-4411. Community of Madrid, Spain. January 2019 ¿ April 2023 - MULTIMAT-CHALLENGE-CM. S2013/MIT-2862 Community of Madrid, Spain. October 2014 ¿ December 2018 The most commonly used aluminium alloys in the aerospace industry are Al-Cu (2xxx series) and Al-Zn (7xxx series) due to their high strength-to-weight ratio. Al-Cu-Li alloys is lightweight and ideal for weight reduction, lighter and stronger parts, involves lower fuel costs in flight. In this work, two Al-Cu-Li alloys have been selected. These alloys are heat-treatable alloys, which contain copper as the main alloying element and have excellent properties as high-strength, high-performance alloys, its main application is in aerospace and aviation sectors. In particular, the addition of lithium in the Al-Cu alloy significantly reduces the density of the alloy while the strength increases much more than with any other alloying element; making the application of this alloying element attractive as ultimately, with its addition, components can reduce the weight of the structure. This unique combination of properties makes these materials very promising candidates for industrial applications with demanding conditions, which has driven the study, design, and development of this family of materials.
The main objective of this thesis is to design and develop new processing routes for Al-Cu-Li alloys to obtain metallic wires, starting from the mixture of elemental powders and master alloys. These new processing routes are based on the powder pressing and extrusion process. With this in mind, four main sections define this work: alloy design, characterisation of the consolidated material, plasma arc welding and application of the wires to WAAM techniques.
Alloy design Al-Cu-Li alloys have always been of great interest to the aerospace industry. Due to their properties, they are excellent for the production of light and strong components. Al-Cu-Li alloys are usually produced by conventional techniques, such as ingot casting and casting techniques. Al-Cu-Li alloys are classified into generations, with the third generation being the most recent and having the best properties. Third-generation Al-Cu-Li alloys are mostly used in structural components such as fuselage panels. The first objective of this doctoral thesis was the consolidation of Al-Cu-Li alloys by powder metallurgical routes to obtain metallic wires and their applicability in WAAM techniques.
For this purpose, two Al-Cu-Li alloys were selected. The two alloys are part of the third generation and can be classified as high-copper, low-lithium alloys and low-lithium, high-copper alloys. Thermodynamic studies were carried out for the selection of the working temperature. The extrusion process parameters were optimised with elemental aluminium powder and then the alloys were consolidated from elemental powder (Mg, Zn, Cu) and master alloys (Al-Li and Al-Mg) by extrusion processes, obtaining bars of 200 mm in length and 5 mm in diameter. According to the microstructural results, a new processing route was proposed. The second processing routine is based on a heat treatment prior to the extrusion process to favour the diffusion processes. Thermodynamic studies were carried out for the selection of the temperature, and different heat treatment tests were carried out on the compacts. Finally, the heat treatment conditions were 525 °C for 1 h under a reducing nitrogen atmosphere. The heat-treated compacts were extruded with optimised extrusion parameters and the bars were characterised.
It can be stated that both proposed processing routes are influenced by the heat treatment. The developed processing methods were simple, reproducible, and scalable and produced high-density Al-Cu-Li alloys. In addition, thermodynamic calculations by Thermo-Calc software were carried out to establish the working temperatures, both in the heat treatment prior to the extrusion process and the temperature of the extrusion process. Although these are theoretical calculations, the phase formation obtained, and the evolution of the alloying elements coincide with the results obtained in the experimental characterisation of the extruded products.
Characterisation of the extruded product After obtaining the bars through the extrusion process, they were characterised in order to validate the properties for the selection of the best acceptable condition to production of wires. This part of the work aims to carry out a complete characterisation using SEM, XRD, EBSD, porosity, oxygen content, hardness, chemical composition and tensile tests.
After optimisation of the sample production, the microstructure was analysed. The microstructural properties of the samples showed a close dependence on the chemical composition of both alloys. Alloy 2196, with lower Mg content, showed a higher porosity than alloy 2060 with higher Mg content. Mg is a key element during heat treatment, as it improves the diffusive process of the alloying elements. The EBSD analysis showed that all the materials exhibit texture, and a preferential orientation along <100> and <111> directions, typical of a duplex fibre texture. The texture is strong for 2060HT and 2196 materials. The hardness values were also represented. The results in the harness for the 2060 extruded can be explained by the fact that the heating previous to the extrusion promotes the dissolution of alloying elements. A better dissolved and hardened alloy makes it more difficult the extrusion while the formation of precipitates is being produced during cooling after extrusion. Thus, significant changes are observed between the 2060 green compact (59 HV) and the 2060 extruded rod (98 HV). 2060 rod is hardened by the strain and precipitation hardening effects. The 2196 alloy shows the lowest hardness values due to the presence of a high number of pores in the microstructure. Chemical analysis showed a loss of the elements Li, Mg and Cu, due to vapour pressure and volatility until 18 %wt. Finally, tensile tests showed better ductility for 2060 alloy due to the more homogeneous microstructure compared to that of the 2196 alloy. In contrast, alloy 2196 shows lower ductility, and the observed fractography showed less developed dimples due to the presence of a higher pore content and particles in the microstructure.
Plasma arc welding In recent years, additive manufacturing (AM) has become a reference technology for the production of prototypes and a new processing route for the development of near-net-shape parts. From the structural purposes of commonly used stainless steels to the functional applications of new materials, AM is a promising avenue for the production of new designs and new materials never before used in industry. One of the main reasons for the booming emergence of Additive Manufacturing in materials processing is the number of technologies it encompasses, allowing the most suitable technologies to be selected for a given material. Plasma arc deposition (PAW) is a wire arc welding (WAAM) technique into the Direct Energy Deposition (DED), which is capable of producing large structures. The process is based on using the wire as a feed material while an electric arc melts it, creating weld beads.
However, it is a necessity to address the lack of WAAM-specific metallic wires. Only some of them are commercially available: 2319, 4018, 5183 and 6063.
In this section, the PAW process was optimised with a commercial wire of similar chemical composition to Al-Cu-Li alloy, 2319 wire. Single tracks of commercial wire 2319 were produced with different welding travel, welding speed and wire feed seed. And their relationship with geometrical parameters: height, width, depth and contact angle were studied. In this study, the effect of various deposition parameters is comprehensively analysed and their interactions in metal plasma deposition of Al alloys. It is well known that the main defects in the Al welding process are porosity and craking, while the more specific defects of the WAAM welding process are delamination, lack of fusion, and bead deviation, among others, and are strongly dependent on the process parameters, which are taken into account in this section. This experimental trial was correlated with a prediction model to help determine the final process parameters (welding travel, welding speed y wire feed seed). The prediction model analyses the cause-effect relationship between the individual input parameters and the measured output deposition track quality aspects, allowing us to identify that the input stream has the greatest effect on the quality of the deposited tracks. In addition, the wire feed speed, and its interaction with the input current, is the second input parameter with the greatest effect. The influence of gases was also tested: shielding gas mixture and shielding gas flow rate mainly affect the penetration depth, while the plasma gas flow rate significantly affects all quality aspects of the measured output deposition track. Furthermore, the selection of the appropriate frequency/balance ratio and/or the preheating of the deposition substrates allows for to reduction of the amount of porosity formed within the deposited tracks. Finally, the selected parameters were used for the implementation of the obtained wire from powder metallurgical routes.
Application of powder metallurgy wires to WAAM techniques The processing of wires by the powder extrusion process is an alternative processing route to solve some problems with WAAM techniques and to produce wires of new compositions. In this case, the chemical composition of the initial 2060 alloy was modified with titanium of different content. Titanium is the most widely used grain refiner and the most powerful one for many Al alloys. Titanium interacts with the Al matrix to form Al3Ti intermetallic. Al3Ti is very attractive because it has a higher melting point ( ~1350°C) and relatively low density ( ~3.3 g/cm3). The main objective of this study is to add an optimal amount of Ti to obtain wires suitable for WAAM. This could improve the final result of material deposition by this technology. Based on the previous study carried out in this work, compacts of composition 2060 with concentrations of 0.1%, 0.3% and 0.6% wt. of Ti were extruded with the previous parameters studied to obtain bars. The compacts and bars were characterised by analysing the titanium content of the samples. The Ti particles were shown to be unchanged at the temperatures used and the hardness values remained unchanged. This suggests that the titanium has so far no obvious effect on the material, as initially proposed. It is desired is that the titanium particles melt during the welding process, thereby activating their influence on the microstructure and beneficial results. In this section the materiales developed from rods and wires with different titanium content from rod and CIP compacts. Both wires were applied to the PAW technology with optimised parameters. The result was weld seams with defects and visible porosity on the surface, however, the bond with the substrate was good. The chemical composition was analysed, obtaining a homogeneous composition thoughth of the weld bead. The main zones (BM, HAZ, FZ) were observed by OM. A deposition study was also carried out on two types of substrates 5083 and 7075. More contamination was observed for the 7075 substrates with a larger HAZ zone.
In summary, rods of 2060 and 2196 alloys have been extruded in this work, and rods of 2060 alloy have been selected as optimal for further investigation. The microstructure quality of the 2196 rods was not good, the low Mg content did not favour the heat treatments, and the presence of porous and non-homogenised alloying elements was observed. Two ways of processing wires were explored, using rods and compacts, and different chemical compositions with Ti were proposed. Characterisation of compacts and rods was carried out prior to wire production to study the suitability of the production of final wires. Finally, the wires were applied to the WAAM technology. The process parameters were previously optimised by means of experimental tests and statistical studies. The wires obtained from rods were applied with the parameters determined. The results were good, in terms of homogeneous chemical composition, and a weld bead with good grip. The same was done with wires of different Ti content, corroborating the intention for which Ti was added, it was found to be dissolved with the rest of the alloying elements and the chemical composition of the bead was completely homogeneous. All this establishes powder metallurgy routes as a possible method of processing Al-Cu-Li alloys to obtain metallic wires for WAAM.
