Microstructural evolution and mechanical property degradation of Al–Cu heat-resistant alloy fabricated by wire-arc directed energy deposition after 300°C thermal exposure

Abstract

High-temperature thermal exposure of Al alloys is used to characterize the real-world performance of components in high-temperature environments. In this study, thin-walled Al–Cu heat-esistant aluminum alloy structures were additively manufactured using a wire-arc directed energy deposition (WA-DED) process. A systematic analysis was conducted to investigate the microstructural changes and determine the cause of mechanical degradation under 300°C thermal exposure. Following T6 heat treatment (solution treatment: 520°C/6 h + 535°C/8 h; aging: 175°C/2 h + 150°C/6 h), the WA-DED 205C (Al–Cu–Mn–Ni–Zr) alloy exhibited a dense distribution of nano-sized θ″, θ′, Al₃Zr, and T (Al₂₀Cu₂Mn₃) phases within the grains, whereas the γ (Al₇Cu₄Ni) phase formed during solidification remained at the grain boundaries. Following thermal exposure at 300°C for 24 h, the majority of θ″ within the grains was supplanted by θ′; a subset of these θ′ subsequently transitioned to θ, while σ (Al₅Cu₆Mg₂) phase concurrently precipitated. As thermal exposure reached 100 h, the θ′ phase exhibited increased particle size alongside reduced number density, whereas the θ phase showed enhanced density and the σ phase was no longer present. The Al₃Zr and T phases within the grains, and the γ phase located at the grain boundaries, showed no significant changes in morphology or size during the thermal exposure process. Furthermore, after thermal exposure at 300°C for 24 h, the microhardness of the T6 condition specimen experienced a sharp decline from HV 149.6 to HV 98.2, and the yield strength (YS) dropped from 353 to 213 MPa. After 100 h of thermal exposure, the microhardness decreased to HV 91.8 and the YS dropped to 196 MPa. The tensile properties of the alloy were stabilized at a YS retention rate of 56%.

Keywords

thermal exposure / heat-resistant aluminum alloy / wire-arc directed energy deposition / mechanical property / thermally stable phase

References

[1] Lin YC, Jiang YQ, Chen XM, Wen DX, Zhou HM. Effect of creep-aging on precipitates of 7075 aluminum alloy. Mater. Sci. Eng. A, 2013, 588: 347.

[2] Li C, Wan M, Wu XD, Huang L. Constitutive equations in creep of 7B04 aluminum alloys. Mater. Sci. Eng. A, 2010, 52716–173623.

[3] Lin B, Li HY, Xu R, et al. Thermal exposure of Al–Si–Cu–Mn–Fe alloys and its contribution to high temperature mechanical properties. J. Mater. Res. Technol., 2020, 921856.

[4] Zhang QH, Li BL, Chen X, Yin JM, Nie ZR, Zuo TY. Characteristic microstructure and microstructure evolution in Al–Cu–Mn alloy under projectile impact. Mater. Sci. Eng. A, 2012, 531: 12.

[5] Liu HB, Hou R, Wu CH, Xie RS, Chen SJ. Multi-layer multi-pass friction rolling additive manufacturing of Al alloy: Toward complex large-scale high-performance components. Int. J. Miner. Metall. Mater., 2025, 322425.

[6] Zuiko I, Kaibyshev R. Effect of plastic deformation on the ageing behaviour of an Al–Cu–Mg alloy with a high Cu/Mg ratio. Mater. Sci. Eng. A, 2018, 737: 401.

[7] N.A. Belov, T.K. Akopyan, N.O. Korotkova, et al., Structure and heat resistance of high strength Al–3.3%Cu–2.5%Mn–0.5%Zr (wt%) conductive wire alloy manufactured by electromagnetic casting, J. Alloy. Compd., 891(2022), art. No. 161948.

[8] Song SY, Gao DL, Feng C, Liu ZY. Effects of thermal exposure on the mechanical properties and microstructure stability of an Al–Cu–Mg–Ag alloy. Adv. Mater. Res., 2012, 554–556: 671.

[9] Li Q, Shenoy RN. DSC and TEM characterizations of thermal stability of an Al–Cu–Mg–Ag alloy. J. Mater. Sci., 1997, 32133401.

[10] F. Czerwinski, Thermal stability of aluminum alloys, Materials, 13(2020), No. 15, art. No. 3441.

[11] Abdelaziz MH, Doty HW, Valtierra S, Samuel FH. Static versus dynamic thermal exposure of transition elements-containing Al–Si–Cu–Mg cast alloy. Mater. Sci. Eng. A, 2019, 739: 499.

[12] Weatherly GC, Nicholson RB. An electron microscope investigation of the interfacial structure of semi-coherent precipitates. Philos. Mag. J. Theor. Exp. Appl. Phys., 1968, 17148801

[13] Kumar AP, Muthaiah VMS, Mula S. Effect of Nb, Y and Zr on thermal stability of nanocrystalline Al–4.5 wt.% Cu alloy prepared by mechanical alloying. J. Alloy. Compd., 2017, 722: 617.

[14] Belov NA, Alabin AN, Matveeva IA. Optimization of phase composition of Al–Cu–Mn–Zr–Sc alloys for rolled products without requirement for solution treatment and quenching. J. Alloy. Compd., 2014, 583: 206.

[15] Zhou XW, Liu ZY, Bai S, Liu M, Ying PY. The influence of various Ag additions on the nucleation and thermal stability of O phase in Al–Cu–Mg alloys. Mater. Sci. Eng. A, 2013, 564: 186.

[16] Bai S, Liu ZY, Ying PY, Wang J, Wang A. Quantitative study of the solute clustering and precipitation in a prestretched Al–Cu–Mg–Ag alloy. J. Alloy. Compd., 2017, 725: 1288.

[17] Z. Yu, Y. Zhang, L. Zhang, et al., Improvement of mechanical properties and thermal stability of Al–Cu–Mg–Ag alloy by warm rolling, Mater. Sci. Eng. A, 880(2023), art. No. 145367.

[18] M.D. Wu, W.S. Liu, D.H. Xiao, and L.P. Huang, Influence of thermal exposure on the microstructure evolution and mechanical behaviors of an Al–Cu–Li alloy, Mater. Des., 227(2023), art. No. 111767.

[19] Cui LY, Liu K, Zhang Z, Chen XG. Enhanced elevatedtemperature mechanical properties of hot-rolled Al–Cu alloys: Effect of zirconium addition and homogenization. J. Mater. Sci., 2023, 582711424.

[20] L. Jiang, B. Rouxel, T. Langan, and T. Dorin, Coupled segregation mechanisms of Sc, Zr and Mn at θ′ interfaces enhances the strength and thermal stability of Al–Cu alloys, Acta Mater., 206(2021), art. No. 116634.

[21] Sun TT, Geng JW, Bian ZY, et al. Enhanced thermal stability and mechanical properties of high-temperature resistant Al-Cu alloy with Zr and Mn micro-alloying. Trans. Nonferrous Met. Soc. China, 2022, 32164.

[22] Zhao DK, Bi GJ, Chen J, et al. A critical review of direct laser additive manufacturing ceramics. Int. J. Miner. Metall. Mater., 2024, 31122607.

[23] Cai XM, Hou Y, Zhang W, et al. Mechanical behavior and response mechanism of porous metal structures manufactured by laser powder bed fusion under compressive loading. Int. J. Miner. Metall. Mater., 2024, 314737.

[24] Li XS, Sukhomlinov D, Que ZQ. Microstructure and thermal properties of dissimilar M300-CuCr₁Zr alloys by multimaterial laser-based powder bed fusion. Int. J. Miner. Metall. Mater., 2024, 311118.

[25] Lin YL, Wang D, Yang C, Zhang WW, Wang Z. An Al-Al interpenetrating-phase composite by 3D printing and hot extrusion. Int. J. Miner. Metall. Mater., 2023, 304678.

[26] Zong HJ, Kang N, Qin ZH, El Mansori M. A review on the multi-scaled structures and mechanical/thermal properties of tool steels fabricated by laser powder bed fusion additive manufacturing. Int. J. Miner. Metall. Mater., 2024, 3151048.

[27] S. Bahl, K. Sisco, Y. Yang, et al., Al–Cu–Ce(–Zr) alloys with an exceptional combination of additive processability and mechanical properties, Addit. Manuf., 48(2021), art. No. 102404.

[28] S.M. Ma, M.L. Wang, Y. Wu, et al., Laser powder bed fusion of an ultrafine microstructural in-situ TiB2/Al composite with excellent mechanical properties and thermal stability at elevated temperatures, Mater. Sci. Eng. A, 891(2024), art. No. 145969.

[29] R.A. Michi, S. Bahl, C.M. Fancher, et al., Load shuffling during creep deformation of an additively manufactured AlCuM-nZr alloy, Acta Mater., 244(2023), art. No. 118557.

[30] Y. Zhou, T.X. Chang, X.W. Fang, R.K. Chen, Y.F. Li, and K. Huang, Tailoring the mechanical properties and thermal stability of additive manufactured micro-alloyed Al–Cu alloy via multi-stage heat treatment, Mater. Des., 233(2023), art. No. 112287.

[31] Y.Z. Zhao, X.P. Guo, S. Hao, Z.W. Zhang, and X.M. Guo, Enhancing high temperature strength of wire arc directed energy deposition Al Cu heat-resistant aluminum alloy by precipitation of thermally stable phase, Mater. Charact., 219(2025), art. No. 114634.

[32] Davydov VG, Rostova TD, Zakharov VV, Filatov YA, Yelagin VI. Scientific principles of making an alloying addition of scandium to aluminium alloys. Mater. Sci. Eng. A, 2000, 280130.

[33] Liu HJ, Cai ZY, Feng Y, Wang M. Microstructure and mechanical properties of wire arc additive manufactured ZL205A alloy. J. Mater. Res. Technol., 2023, 26: 5321.

[34] Y.H. Zhou, Z.N. Wang, X. Lin, et al., Impact toughness and fractography of diverse microstructure in Al–Cu alloy fabricated by arc-directed energy deposition, Addit. Manuf., 63(2023), art. No. 103414.

[35] Zuiko I, Kaibyshev R. Aging behavior of an Al–Cu–Mg alloy. J. Alloy. Compd., 2018, 759: 108.

[36] Wu CT. Effects of scandium addition and T7 heat treatment on thermal stability and corrosion properties of A201 alloy. J. Mater. Eng. Perform., 2018, 271304.

[37] Biswas A, Siegel DJ, Wolverton C, Seidman DN. Precipitates in Al–Cu alloys revisited: Atom-probe tomographic experiments and first-principles calculations of compositional evolution and interfacial segregation. Acta Mater., 2011, 59156187.

[38] Ringer SP, Sofyan BT, Prasad KS, Quan GC. Precipitation reactions in Al–4.0Cu–0.3Mg (wt.%) alloy. Acta Mater., 2008, 5692147.

[39] Wang F, Qiu D, Liu ZL, Taylor J, Easton M, Zhang MX. Crystallographic study of Al₃Zr and Al₃Nb as grain refiners for Al alloys. Trans. Nonferrous Met. Soc. China, 2014, 2472034.

[40] Wang SC, Li CZ, Yan MG. Determination of structure of Al20Cu2Mn3 phase in Al–Cu–Mn alloys. Mater. Res. Bull., 1989, 24101267.

[41] Y.Q. Chen, Z.H. Tang, S.P. Pan, et al., A new type of anti-phase boundaries in the T(Al₂₀Cu₂Mn₃) phase and the pre-deformation effect on T phase precipitation, Intermetallics, 127(2020), art. No. 106977.

[42] H.B. Dai, F. Liu, Y.H. Xia, B.L. Dong, X.Y. Cai, and S.B. Lin, Wire arc additive manufacturing of the Al–5.55Cu alloy: Insight the effect of intrinsic heat treatment on microstructure and mechanical properties, Mater. Charact., 211(2024), art. No. 113859.

[43] Li Q, Wawner FE. Characterization of a cubic phase in an Al–Cu–Mg–Ag alloy. J. Mater. Sci., 1997, 32205363.

[44] Lumley RN, Polmear IJ. The effect of long term creep exposure on the microstructure and properties of an underaged Al–Cu–Mg–Ag alloy. Scripta Mater., 2004, 5091227.

[45] Liu L, Xu WH, Li Y, et al. Investigation the effects of friction stir processing on microstructure and mechanical properties of Al–Cu alloy fabricated by wire arc additive manufacturing. J. Mater. Res. Technol., 2025, 34: 539.

[46] C.P. Xue, Y.X. Zhang, P.C. Mao, et al., Improving mechanical properties of wire arc additively manufactured AA2196 Al–Li alloy by controlling solidification defects, Addit. Manuf., 43(2021), art. No. 102019.

[47] Zhang XY, Xu RZ, Guo XM, Sun TJ, Zhang ZW. Improving the microstructure and properties of 205A alloys fabricated by wire-arc directed energy deposition using ultrasonic impact treatment. Sci. Technol. Weld. Join., 2025, 304305.

[48] Rakhmonov J, Liu K, Chen GX. Effects of compositional variation on the thermal stability of θ′-Al₂Cu precipitates and elevated-temperature strengths in Al–Cu 206 alloys. J. Mater. Eng. Perform., 2020, 29117221.

[49] Knipling KE, Dunand DC, Seidman DN. Criteria for developing castable, creep-resistant aluminum-based alloys–A review. Zeitschrift für Metallkunde, 2006, 973246.

[50] Guo ZY, Zhao G, Chen XG. Effects of two-step homogenization on precipitation behavior of Al₃Zr dispersoids and recrystallization resistance in 7150 aluminum alloy. Mater. Charact., 2015, 102: 122.

[51] S.M. Dar and H.C. Liao, Creep behavior of heat resistant Al–Cu–Mn alloys strengthened by fine (θ′) and coarse (Al₂₀Cu₂Mn₃) second phase particles, Mater. Sci. Eng. A, 763(2019), art. No. 138062.

[52] Zupanič F, Wang D, Gspan C, Bončina T. Precipitates in a quasicrystal-strengthened Al–Mn–Be–Cu alloy. Mater. Charact., 2015, 106: 93.

[53] Chen YQ, Pan SP, Tang SW, Liu WH, Tang CP, Xu FY. Formation mechanisms and evolution of precipitate-free zones at grain boundaries in an Al–Cu–Mg–Mn alloy during homogenisation. J. Mater. Sci., 2016, 51167780.

[54] Chen YQ, Pan SP, Liu WH, Liu X, Tang CP. Morphologies, orientation relationships, and evolution of the T-phase in an Al–Cu–Mg–Mn alloy during homogenisation. J. Alloy. Compd., 2017, 709: 213.

[55] Rodrigues AV, Lima TS, Almeida Vida T, Brito C, Garcia A, Cheung N. Microstructure features and mechanical/electrochemical behavior of directionally solidified Al–6wt.%Cu–5wt.%Ni alloy. Trans. Nonferrous Met. Soc. China, 2021, 3161529.

[56] E.M. Ahmed and E.S. Gouda, Microstructure and physical properties of melt spun Al–17 wt.% Ni–10 wt.% Cu alloy, Eur. Phys. J. Appl. Phys., 50(2010), No. 2, art. No. 21301.

[57] Hafez HA, Farag MM. Effect of structure on the Young’s modulus of Al–Cu–Ni alloys. J. Mater. Sci., 1981, 1651223.

[58] Batchvarov R, Stanev L, Stanev S, Maneva A, Georguiev M, Nenova L. Structural features and possibilities for increasing the operating temperature of aluminum alloys. Int. J. NDT Days, 2020, 35279

[59] X. Su, H.J. Qu, Y. Lei, et al., Influence of Ni on the microstructures and mechanical properties of heat-treated Al–Cu–Ce–Mn–Zr alloys, Crystals, 13(2023), No. 3, art. No. 380.

[60] Song YF, Pan QL, Wang Y, Li C, Feng L. Elevatedtemperature mechanical properties and thermal stability of Al–Cu–Mg–Ag heat-resistant alloy. J. Cent. South Univ., 2014, 2193434.

[61] Chen BA, Liu G, Wang RH, et al. Effect of interfacial solute segregation on ductile fracture of Al–Cu–Sc alloys. Acta Mater., 2013, 6151676.

[62] Lin B, He XX, Zhao YL, Xu R, Lu YM. Evolution of iron-rich intermetallics and its effect on the mechanical properties of Al–Cu–Mn–Fe–Si alloys after thermal exposure and high-temperature tensile testing. J. Mater. Res. Technol., 2023, 23: 2527.

[63] J. Rakhmonov, K. Liu, L. Pan, F. Breton, and X.G. Chen, Enhanced mechanical properties of high-temperature-resistant Al–Cu cast alloy by microalloying with Mg, J. Alloy. Compd., 827(2020), art. No. 154305.

[64] S. Bahl, L.H. Xiong, L.F. Allard, et al., Aging behavior and strengthening mechanisms of coarsening resistant metastable θ′ precipitates in an Al–Cu alloy, Mater. Des., 198(2021), art. No. 109378.

[65] P. Shower, J. Morris, D. Shin, B. Radhakrishnan, J. Poplawsky, and A. Shyam, Mechanisms for stabilizing θ′ (Al₂Cu) precipitates at elevated temperatures investigated with phase field modeling, Materialia, 6(2019), art. No. 100335.

[66] Shin D, Shyam A, Lee S, Yamamoto Y, Haynes JA. Solute segregation at the Al/θ′-Al₂Cu interface in Al–Cu alloys. Acta Mater., 2017, 141: 327.

[67] U. Bansal, M.P. Singh, S.K. Sinha, et al., Strength and stability through variable micro segregation behaviour of Ta and Zr solutes at intermetallic interfaces in Al–Cu alloys, Acta Mater., 259(2023), art. No. 119254.

[68] Wang J, Zhang B, He ZB, Wu B, Ma XL. Atomic-scale mapping of twins and relevant defective structures in Al₂₀Cu₂Mn₃ decagonal approximant. Philos. Mag., 2016, 96232457.

[69] Wang GJ, Xiong BQ, Zhang YA, Li ZH, Li PY. Microstructural characterization of as-cast and homogenized 2D70 aluminum alloy. Int. J. Miner. Metall. Mater., 2009, 164427.

[70] Zhou YR, Liu ZY, Bai S, Ying PY, Lin LH. Effect of Ag additions on the lengthening rate of Ω plates and formation of σ phase in Al–Cu–Mg alloys during thermal exposure. Mater. Charact., 2017, 123: 1.

[71] Mondol S, Makineni SK, Kumar S, Chattopadhyay K. Enhancement of high temperature strength of 2219 alloys through small additions of Nb and Zr and a novel heat treatment. Metall. Mater. Trans. A, 2018, 4973047.

[72] Z.J. Tan, K. Yu, C.Y. Zeng, et al., Porosity suppression and mechanical property improvement of wire-arc directed energy deposited TiCp/Al–Cu alloys joint by oscillating pulsed wave laser beam welding, J. Mater. Process. Technol., 329(2024), art. No. 118458.

[73] Roy S, Allard LF, Rodriguez A, Porter WD, Shyam A. Comparative evaluation of cast aluminum alloys for automotive cylinder heads: Part II: Mechanical and thermal properties. Metall. Mater. Trans. A, 2017, 4852543.

[74] Lv PH, Wang RC, Peng CQ, Cai ZY, Feng Y, Peng X. The evolution of precipitates and mechanical properties in rapidly solidified 2195 Al–Cu–Li alloy during thermal exposure. J. Mater. Res. Technol., 2023, 27: 6159.

[75] Tsivoulas D, Robson JD, Sigli C, Prangnell PB. Interactions between zirconium and manganese dispersoid-forming elements on their combined addition in Al–Cu–Li alloys. Acta Mater., 2012, 6013–145245.

[76] Shen FH, Wang B, Liu HQ, et al. Effects of secondary particle-induced recrystallization on fatigue crack growth in AA2524/Al Cu Mg T3 alloy sheets. J. Alloy. Compd., 2016, 685: 571.

[77] Kang FW, Xu P, Wang EH, et al. Influences of Ni addition on microstructure and mechanical properties of cast aluminum alloy 207. J. Mater. Eng. Perform., 2024, 33189761.

Rights & permissions

University of Science and Technology Beijing