Enhanced Fe tolerance in recycled Al–7Si–0.3Mg alloys via refining microstructure

Abstract

A key challenge in Al recycling involves controlling the Fe content and resultant Fe-rich intermetallic compound (IMC), as these incur a detrimental effect on ductility. This study evaluated the critical Fe content (0.17wt% for β-Al₅FeSi formation in Al–7Si–0.3Mg alloys) and achievable Fe tolerance (the maximum Fe content focusing on the 0.2Fe–0.02Sr alloy) required for an optimized eutectic Si morphology. The individual and combined additions of Mn (Fe-rich IMCs refinement element) and Nb (α-Al refinement element) in recycled alloys without abrupt elongation (EL) deterioration were distinguished using thermodynamic calculation and experimental determination. The contribution of alloying to the maximum EL (approximately 100%) of Al–7Si–0.3Mg–0.2Fe alloy at a cooling rate of 2°C/s was determined by comparing the effects of individual and overall modifications, targeting Fe-rich IMCs, α-Al, and eutectic Si, on mechanical properties. The same microstructural refinement effect achieved by the overall alloying modification was obtained through the addition of Sr and accelerated cooling (from 2 to 6°C/s). A 317% improvement in EL at 0.2wt% Fe was achieved through this synergistic refinement, demonstrating its superior effectiveness in enhancing ductility. Furthermore, microstructure analysis revealed that the secondary dendrite arm spacing was the most critical factor influencing Fe tolerance in this alloy. By contrast, the refinement of the Fe-rich IMCs, although beneficial, did not contribute significantly to improving Fe tolerance. This strategy enables the utilization of high-Fe Al scrap to advance the sustainability of the Al recycling industry.

Keywords

Al–7Si–0.3Mg alloys / Fe tolerance / critical Fe contents / mechanical properties / refining microstructure

References

[1] Y.F. Zhang, X.L. Luo, L.F. Zhu, et al., Design of non-heat-treatable Al–Fe–Ni alloys with high electrical conductivity and high strength via CALPHAD approach, J. Alloy. Compd., 1009(2024), art. No. 176920.

[2] Chen YJ, Chen HC, Yang SL, et al. Prediction of viscosity of Mg and Al alloy melts by machine learning. J. Mater. Sci., 2025, 60198133.

[3] Li JJ, Yu WB, Sun ZY, et al. Influence of introducing Zr, Ti, Nb and Ce elements on externally solidified crystals and mechanical properties of high-pressure die-casting Al–Si alloy. Int. J. Miner. Metall. Mater., 2025, 321147.

[4] Yang JH, Wu LY, Lian Y, et al. Texture, residual stress and mechanical properties of 7039-T6 thick plate Al alloy with MIG-welded laminar tearing. Int. J. Miner. Metall. Mater., 2025, 3251176.

[5] Yuan LL, Guo MX, Wang Y, Wang Y, Zhuang LZ. Synergistic effect of gradient Zn content and multiscale particles on the mechanical properties of Al–Zn–Mg–Cu alloys with coupling distribution of coarse–fine grains. Int. J. Miner. Metall. Mater., 2024, 3161392.

[6] H. Nunes, O. Emadinia, R. Soares, M.F. Vieira, and A. Reis, Adding value to secondary aluminum casting alloys: A review on trends and achievements, Materials, 16(2023), No. 3, art. No. 895.

[7] Liu YQ, Wang M, Cao Y, et al. Revealing the effect of iron content on the microstructure evolution, mechanical properties and corrosion resistance of the A356-T6 aluminum alloys. J. Mater. Res. Technol., 2024, 33: 2263.

[8] Yu JM, Wanderka N, Rack A, et al. Formation of intermetallic δ phase in Al–10Si–0.3Fe alloy investigated by in-situ 4D X-ray synchrotron tomography. Acta Mater., 2017, 129: 194.

[9] Zhan HY, Zeng G, Wang QG, et al. Unified casting (Uni-Cast) aluminum alloy—A sustainable and low-carbon materials solution for vehicle lightweighting. J. Mater. Sci. Technol., 2023, 154: 251.

[10] Balasubramani N, Moodispaw M, Luo AA. Controlling the Fe-intermetallic phases and mechanical properties of secondary Al–9Si–1Fe alloy with Cr and Mn additions. J. Mater. Sci. Technol., 2025, 206: 135.

[11] Hassani A, Ranjbar K, Sami S. Microstructural evolution and intermetallic formation in Al–8wt% Si–0.8wt% Fe alloy due to grain refiner and modifier additions. Int. J. Miner. Metall. Mater., 2012, 198739.

[12] Lu L, Dahle AK. Iron-rich intermetallic phases and their role in casting defect formation in hypoeutectic Al–Si alloys. Metall. Mater. Trans. A, 2005, 3613819.

[13] J. Lazaro-Nebreda, J.B. Patel, I.T.H. Chang, I.C. Stone, and Z. Fan, Solidification processing of scrap Al-alloys containing high levels of Fe, IOP Conf. Ser.: Mater. Sci. Eng., 529(2019), art. No. 012059.

[14] Kishor M, Chopra K, Ayyagari KPR. Tackling Fe-rich Intermetallics in Al–Si Alloy: A Critical Review. Trans. Indian Inst. Met., 2024, 77103031.

[15] X.Y. Lan, K. Li, J. Wang, M.J. Yang, Q. Lu, and Y. Du, Developing Al–Fe–Si alloys with high thermal stability through tuning Fe, Si contents and cooling rates, Intermetallics, 144(2022), art. No. 107505.

[16] Narayanan LA, Samuel FH, Gruzleski JE. Crystallization behavior of iron-containing intermetallic compounds in 319 aluminum alloy. Metall. Mater. Trans. A, 1994, 2581761.

[17] Taylor JA. Iron-containing intermetallic phases in Al–Si based casting alloys. Procedia Mater. Sci., 2012, 1: 19.

[18] Gan JQ, Du J, Wen C, Zhang GG, Shi MB, Yuan ZZ. The effect of Fe content on the solidification pathway, microstructure and thermal conductivity of hypoeutectic Al–Si alloys. Int. J. Metalcast., 2022, 161178.

[19] W. Mohammed, X.R. Chen, D. Ponge, and D. Raabe, Thermodynamics-guided design of sustainable secondary Al–Si alloys for enhanced Fe-impurity tolerance and optimized Mn doping, Acta Mater., 289(2025), art. No. 120932.

[20] Zou J, Zhang HT, Yu C, et al. Investigating the influences of Fe, Mn and Mo additions on the evolution of microstructure and mechanical performances of Al–Si–Mg cast alloys. J. Mater. Res. Technol., 2023, 25: 319.

[21] Kim HY, Han SW, Lee HM. The influence of Mn and Cr on the tensile properties of A356–0.20Fe alloy. Mater. Lett., 2006, 60151880.

[22] B. Wang, J.S. Wang, X.X. Liu, Q. Li, and X.G. Liu, Uncovering the effects of neutralizing elements (Co, Mn and Cr) on the Fe-rich intermetallic formation in Al–Si–Cu alloys, Mater. Sci. Eng. A, 858(2022), art. No. 144090.

[23] Zhang XZ, Wang DT, Nagaumi H, et al. Unveiling the growth mechanism of Fe-containing intermetallics in Al–Si alloy in the perspective of surface stability and atom adsorption. J. Mater. Res. Technol., 2025, 35: 2458.

[24] B. Wang, X.X. Liu, J.S. Wang, Q. Li, K.L. Liu, and M.S. Zhang, Uncovering the effects of Ce and superheat temperature on Fe-rich intermetallic and microporosity formation in aluminum alloy, Mater. Charact., 193(2022), art. No. 112226.

[25] Z.H. An, W.H. Yang, H.Y. Zhan, et al., On the strengthening effect of Al–Cr–Si dispersoid in an Al–Si–Mg–Cu casting alloy with Cr addition, Mater. Charact., 166(2020), art. No. 110457.

[26] Fan C, Long SY, Yang HD, Wang XJ, Zhang JC. Influence of Ce and Mn addition on α-Fe morphology in recycled Al–Si alloy ingots. Int. J. Miner. Metall. Mater., 2013, 209890.

[27] Li Y, Hu B, Liu B, et al. Insight into Si poisoning on grain refinement of Al–Si/Al–5Ti–B system. Acta Mater., 2020, 187: 51.

[28] D.X. Li, X.R. Yan, Y. Fan, et al., An anti Si/Zr-poisoning strategy of Al grain refinement by the evolving effect of doped complex, Acta Mater., 249(2023), art. No. 118812.

[29] Li Y, Jiang Y, Liu B, Luo Q, Hu B, Li Q. Understanding grain refining and anti Si-poisoning effect in Al–10Si/Al–5Nb–B system. J. Mater. Sci. Technol., 2021, 65: 190.

[30] Zhao CX, Li Y, Xu J, et al. Enhanced grain refinement of Al–Si alloys by novel Al–V–B refiners. J. Mater. Sci. Technol., 2021, 94: 104.

[31] Zhao ZY, Li DX, Yan XR, et al. Insights into the dual effects of Ti on the grain refinement and mechanical properties of hypoeutectic Al–Si alloys. J. Mater. Sci. Technol., 2024, 189: 44.

[32] Zhu LF, Zhang Y, Luo Q, Peng LM, Li Q. Effectively refining Al–10Si alloy via Al–Ti–Nb–B refiner with Nb₂O₅. J. Mater. Sci. Technol., 2024, 176: 204.

[33] Li Y, Hu B, Gu QF, Liu B, Li Q. Achievement in grain-refining hypoeutectic Al–Si alloys with Nb. Scripta Mater., 2019, 160: 75.

[34] Li Y, Jiang Y, Hu B, Li Q. Novel Al–Ti–Nb–B grain refiners with superior efficiency for Al–Si alloys. Scripta Mater., 2020, 187: 262.

[35] Xu J, Li Y, Ma K, et al. In-situ observation of grain refinement dynamics of hypoeutectic Al–Si alloy inoculated by Al–Ti–Nb–B alloy. Scripta Mater., 2020, 187: 142.

[36] Xu J, Li Y, Hu B, Jiang Y, Li Q. Development of Al–Nb–B master alloy with high Nb/B ratio for grain refinement of hypoeutectic Al–Si cast alloys. J. Mater. Sci., 2019, 542314561.

[37] Fatahalla N, Hafiz M, Abdulkhalek M. Effect of micro-structure on the mechanical properties and fracture of commercial hypoeutectic Al–Si alloy modified with Na, Sb and Sr. J. Mater. Sci., 1999, 34143555.

[38] McDonald SD, Nogita K, Dahle AK. Eutectic nucleation in Al–Si alloys. Acta Mater., 2004, 52144273.

[39] Liao HC, Sun GX. Mutual poisoning effect between Sr and B in Al–Si casting alloys. Scripta Mater., 2003, 4881035.

[40] Luo Q, Li XR, Li Q, et al. Achieving grain refinement of α-Al and Si modification simultaneously by La–B–Sr addition in Al–10Si alloys. J. Mater. Sci. Technol., 2023, 135: 97.

[41] Jiao XY, Liu CF, Guo ZP, et al. The characterization of Fe-rich phases in a high-pressure die cast hypoeutectic aluminum–silicon alloy. J. Mater. Sci. Technol., 2020, 51: 54.

[42] Liu YL, Luo L, Han CF, Ou LY, Wang JJ, Liu CZ. Effect of Fe, Si and cooling rate on the formation of Fe- and Mn-rich intermetallics in Al–5Mg–0.8Mn alloy. J. Mater. Sci. Technol., 2016, 324305.

[43] D.H. Kim, J.H. Kim, and E. Kobayashi, Microstructure characterization of rolled Al–Si–Mg–Fe alloy by three-dimensional tomography, Mater. Sci. Eng. A, 768(2019), art. No. 138449.

[44] L.F. Zhu, Q. Luo, Q.C. Chen, et al., Prediction of ultimate tensile strength of Al–Si alloys based on multimodal fusion learning, Mater. Genome Eng. Adv., 2(2024), No. 1, art. No. e26.

[45] Y. Fu, Q. Luo, B. Liu, and Q. Li, Viscosity calculation for Al–Si–Mg–Fe system through CALPHAD method, Adv. Eng. Mater., 26(2024), No. 20, art. No. 2400941.

[46] Yin T, Guo Y, Ma Z, et al. Experimental study and thermodynamic modeling of the phase equilibria in the Mg-rich corner of Mg–Zn–Mn system. Int. J. Miner. Metall. Mater., 2025, 32102523.

[47] Li HX, Xu WJ, Zhang YF, et al. Prediction of the thermal conductivity of Mg–Al–La alloys by CALPHAD method. Int. J. Miner. Metall. Mater., 2024, 311129.

[48] Chen HC, Wen HB, Sun JL, et al. Quantitative exploration of aging-precipitate-property relationship in Mg–Gd alloys. J. Mater. Sci. Technol., 2026, 245: 221.

[49] H.C. Chen, J.L. Sun, S.L. Yang, et al., Thermodynamics and kinetics of isothermal precipitation in magnesium alloys, Mater. Genome Eng. Adv., 3(2025), No. 1, art. No. e86.

[50] S.K. Feng, M. Shearwood, A. Lui, et al., Probing the mechanisms of morphological evolution and phase selection of inter-metallic compounds for impurity-tolerant processing of recycled Al alloys, Acta Mater., 301(2025), art. No. 121591.

[51] Li JH, Albu M, Hofer F, Schumacher P. Solute adsorption and entrapment during eutectic Si growth in A–Si-based alloys. Acta Mater., 2015, 83: 187.

[52] Liu XR, Zhang YD, Beausir B, et al. Twin-controlled growth of eutectic Si in unmodified and Sr-modified Al–12.7%Si alloys investigated by SEM/EBSD. Acta Mater., 2015, 97: 338.

[53] H. Becker, T. Bergh, P.E. Vullum, A. Leineweber, and Y. Li, Effect of Mn and cooling rates on α-, β- and δ-Al–Fe–Si intermetallic phase formation in a secondary Al–Si alloy, Materialia, 5(2019), art. No. 100198.

[54] D.F. Song, Y.L. Zhao, Y.W. Jia, et al., Study of the evolution mechanisms of Fe-rich phases in Al–Si–Fe alloys with Mn modification using synchrotron X-ray imaging, J. Alloy. Compd., 915(2022), art. No.165378.

[55] Kral MV, Nakashima PNH, Mitchell DRG. Electron microscope studies of Al–Fe–Si intermetallics in an Al–11 Pct Si alloy. Metall. Mater. Trans. A, 2006, 37: 1987.

[56] Z.P. Que and C.L. Mendis, Formation of θ-A1₁₃Fe₄ and the multi-step phase transformations to α-Al₈Fe₂Si, β-Al₅FeSi and δ-Al₄FeSi₂ in Al–20Si–0.7Fe alloy, Intermetallics, 127(2020), art. No. 106960.

[57] Becker H, Bergh T, Vullum PE, Leineweber A, Li Y. β- and δ-Al–Fe–Si intermetallic phase, their intergrowth and polytype formation. J. Alloy. Compd., 2019, 780: 917.

[58] Dinnis CM, Taylor JA, Dahle AK. As-cast morphology of iron-intermetallics in Al–Si foundry alloys. Scripta Mater., 2005, 538955.

[59] Schmid-Fetzer R, Kozlov A. Thermodynamic aspects of grain growth restriction in multicomponent alloy solidification. Acta Mater., 2011, 59156133.

[60] Yajjala RK, Inampudi NM, Jinugu BR. Correlation between SDAS and mechanical properties of Al–Si alloy made in Sand and Slag moulds. J. Mater. Res. Technol., 2020, 936257.

[61] Eidhed W. Modification of β-Al₅FeSi compound in recycled Al–Si–Fe cast alloy by using Sr, Mg and Cr additions. J. Mater. Sci. Technol., 2008, 24145

[62] Wei YS, Wang C, You J, et al. Substantial grain refinement of Al–Mn–Si alloys mediated by collaborative effect of Al–5Ti–1B refiner and sub-rapid solidification. J. Mater. Sci. Technol., 2024, 187: 230.

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