Liu Weidong;Qu Hua;Feng Xiangyu;Cui Qinghui;Zhu Wei;

• 1:School of Materials Science and Engineering
• 2:Liaoning University of Technology

Abstract：

Al-Cu alloys have been widely applied in various industries such as aerospace,mechanical manufacturing,automobiles,and electronic equipment due to their excellent mechanical properties,good heat resistance,and processing performance.These alloys can achieve strength enhancement through the interaction between the series of strengthening phases precipitated during the aging process and the matrix.θ' and θ phases precipitated on the {001}_α surface and Ω phase precipitated on the {111}_α surface are the main strengthening phases,and their compositions are all Al_2Cu.The valence electron structures of Al_2Cu and Al_2Cu/α phase interface have an important influence on the strength and toughness of Al-Cu alloys.Based on the analysis of atomic valence electron states,the empirical electron theory of solids and molecules(EET) can reveal the intrinsic relationship between the microscopic structure and macroscopic properties(such as strength,hardness,stability,interface continuity,etc.) through the bond length difference method(BLD) to calculate the valence electron structure parameters of materials.The EET theory can provide a theoretical basis for understanding the aging strengthening mechanism,phase stability and mechanical property optimization of the alloys after analyzing the valence electron structures of strengthening phases(such as θ',θ and Ω) and phase interfaces in the research works of Al-Cu alloys.Based on the EET theory,the valence electron structures of matrix α,main strengthening phases(θ',θ and Ω),and phase interfaces of θ'/α,θ/α and Ω/α were calculated.The stability and precipitation hardening capacity of θ',θ and Ω phases were comparatively analyzed with the strongest bond covalent electron number n_1,total bonding capacity F,atomic state group number σ_p,and bulk covalent electron density ρ_c. At the same time,the binding force and continuity of the phase interfaces of θ'/α,θ/α and Ω/α were analyzed with the face-centered covalent electron density ρ and the covalent electron density difference Δρ.The results showed that because of the strongest bond covalent electron number n_1~θ> n_1~(θ')> n_1~Ω,the strongest bond force of Ω on the dislocation main slip plane {111} was 7.25% and 13.47% respectively smaller than that of θ' and θ' on the {001} plane,but the hindering effect on dislocation movement was stronger.Compared with θ' and θ,Ω was more stable with greater strength and hardness,stronger precipitation hardening ability owing to total bonding capacity F~Ω>F~θ>F~(θ'),total bonding capacity σ_ρ~Ω>σ_ρ~(θ')>σ_p~θ and,bulk covalent electron density ρ_c~Ω>ρ_c~(θ')>ρ_c~θ.The face-centered covalent electron density ρ_α~((111)) was 94.32% higher than those of θ'/α and θ/α,ρ_Ω~((001)) was 66.84%,512.22% respectively higher than ρ_(θ')~((001)) of θ'/α and ρ_θ~((001)) ofθ/α,the covalent electron density difference Δρ_(θ'/α) was 10.41%,Δρ_(θ/α) was 97.09% and Δρ_(Ω/α) was 8.79%,so Δρ_(Ω/α) was the smallest and Ω/α interface had stronger binding force and better continuity compared with that of θ'/α and θ/α.Compared with the valence electron structures of phase space of θ',θ and Ω,the atomic states and outer electron arrangements on the θ',θ and Ω sides of the interface θ'/α,θ/α and Ω/α have been adjusted to lower ρ_(θ')~((001)) and ρ_Ω~((001)) while increased ρ_θ~((001)) and reduced the difference between ρ_α~((001)) and ρ_α~((111)) on the α side,so the continuity of the phase interface was improved.The valence electron structures calculations results of phase space and phase interface indicated that compared with θ' and θ Ω was more stable with stronger hindering effect on dislocations,greater strength and stronger bonding force with the matrix,therefore it had more contribution to the strength and toughness of the alloy.By calculating the valence electron structures of Al_2Cu in Al-Cu alloys and the phase interface between Al_2Cu and the matrix α to compare and analyze the stability of the phases,the precipitation hardening capacity,as well as the bonding force and continuity of the phase interface,the influence of the valence electron structures on the alloy properties can be revealed at the valence electron structure level.

Key Words： Al-Cu alloy;Al_2Cu;phase space;phase interface;valence electron structure;empirical electron theory

Abstract:

Keywords:

Foundation: 辽宁省教育厅面上项目(LJKMZ20220958,LJK20621);; 辽宁省“兴辽英才计划”教学名师项目(XLYC221026)资助

Authors: Liu Weidong;Qu Hua;Feng Xiangyu;Cui Qinghui;Zhu Wei;

DOI: 10.13373/j.cnki.cjrm.XY25080006

References：

• [1] Wang S B, Liu Z R, Xia S L, Key J, Chen J H. Tetragonalprism-like Guinier-Preston-Bagaryatsky zones in an AlCuMg alloy[J]. Materials Characterization, 2017, 132: 139.
• [2] Wang Y H, Wang J T, Yang H, Huang T J, Zhang R Y, Zheng C, Guo F J. Influence of cold rolling and annealing methods on microstructure of 2 series aviation aluminium alloy sheet[J]. Forging and Stamping Technology, 2025, 50(8): 185.（王永红，王经涛，杨航，黄同瑊，张芮源，郑铖，郭丰佳. 冷轧和退火方式对2系航空铝合金薄板显微组织的影响[J]. 锻压技术，2025, 50(8): 185.）
• [3] Liu Z Y, Li Y T, Liu Y B, Xia Q K. Development of Al-CuMg-Ag alloys[J]. The Chinese Journal of Nonferrous Metals, 2007, 17(12): 1905.（刘志义， 李云涛， 刘延斌， 夏卿坤 . Al-Cu-Mg-Ag 合金析出相的研究进展[J]. 中国有色金属学报，2007, 17(12): 1905.）
• [4] Yin J R, Chen J H, Cheng X X, Qiu Q Q, Wang W X, Weng Y Y. Micro-structure of Al-Cu alloys for automobile engines with multistage solution treatment and Sc microalloying[J]. Chinese Journal of Rare Metals, 2026, 49(3): 342.（殷嘉蓉， 陈家浩， 程翔翔， 邱铨强， 王文鑫， 翁瑶瑶 . 多级固溶处理及Sc微合金化对汽车发动机用Al-Cu合金微观结构的影响[J]. 稀有金属，2026, 49(3): 342.）
• [5] Bahl S, Xiong L H, Allard L F, Michi R A, Poplawsky J D, Chuang A C, Singh D, Watkins T R, Shin D, Haynes J A, Shyam A. Aging behavior and strengthening mechanisms of coarsening resistant metastable θ'precipitates in an Al-Cu alloy[J]. Materials and Design, 2021, 198: 109378.
• [6] Takeda M, Madea Y, Yoshida A, Yabuta K, Konuma S, Endo T. Discontinuity of G.P.(I) zone and θ″-phase in an AlCu alloy[J]. Scripta Materialia, 1999, 41(6): 643.
• [7] Bai S, Liu Z Y, Zhou X W, Xia P, Zeng S M. Mg-controlled formation of Mg-Ag co-clusters in initial aged Al-Cu-Mg-Ag alloys[J]. Journal of Alloys and Compounds, 2014, 602: 193.
• [8] Fan J C, Yang B W, Wang Y, Gao M Q, Guan R G. Enhancing the tensile strength and heat resistance induced by high-density Ω phases in an Al-Cu-Mg-Ag alloy[J]. Journal of Materials Research and Technology, 2022, 18: 3347.
• [9] Gable B M, Shiflet G J, Starke E A Jr. Alloy development for the enhanced stability of Ω precipitates in Al-Cu-MgAg alloys[J]. Metallurgical and Materials Transactions A, 2006, 37A: 1091.
• [10] Lumley R N, Polmear I J. The effect of long term creep exposure on the microstructure and properties of an under aged Al-Cu-Mg-Ag alloy[J]. Scripta Materialia, 2004, 50(9): 1227.
• [11] Hutchinson C R, Fan X, Pennycook S J, Shiflet G J. On the origin of the high coarsening resistance of omega plates in Al-Cu-Mg-Ag alloys[J]. Acta Materialia, 2001, 49: 2827.
• [12] Kang S J, Kim Y W, Kima M, Zuo J M. Determination of interfacial atomic structure, misfits and energetics of Ω phase in Al-Cu-Mg-Ag alloy[J]. Acta Materialia, 2014, 81: 501.
• [13] Yu Z, Li H, Cai P Z, Fu X X, Feng Z Q, Zhang L, Wang J S, Xiao N M. Effect of aging route on the precipitation behavior and thermal stability of Al-Cu-Mg-Ag alloy[J]. Journal of Materials Research and Technology, 2023, 23: 2010.
• [14] Zhang R L. Empirical Electron Theory of Solids and Molecules[M]. Changchun: Jilin Science and Technology Press, 1993. 1.（张瑞林 . 固体与分子经验电子理论 [M]. 长春： 吉林科学技术出版社，1993. 1.）
• [15] Liu Z L, Li Z L, Liu W D. Valence Electron Structure of Interface and Their Properties[M]. Beijing: Science Press, 2002. 1.（刘志林， 李志林， 刘伟东 . 界面价电子结构与界面性能 [M]. 北京： 科学出版社，2002. 1.）
• [16] Hou Y H, Li G Q, Liu Z Y, Fan X A. Study on the strengthening mechanism of Al-Cu-Mg-Ag alloy with the valence electron structures and atomic bonding of precipitates[J]. Rare Metal Materials and Engineering, 2011, 40(3): 407.（侯延辉， 李光强， 刘志义， 樊希安 . 从电子结构和成键特性分析高Cu/Mg比Al-Cu-Mg-Ag合金强化机制[J]. 稀有金属材料与工程，2011, 40(3): 407.）
• [17] Jing Y J, Li C R, Du Z M, Wang F M, Song Y P. Coherent electron structure of GP zones in Al-Cu alloy and interfacial energy between GP zones and matrix[J]. Transactions of Materials and Heat Treatment, 2007, 28(6): 148.（静永娟， 李长荣， 杜振民， 王福明， 宋月鹏 . Al-Cu 合金GP区的价电子结构与界面能[J]. 材料热处理学报，2007, 28(6): 148.）
• [18] Jiang S Y, Li S C. Valence electron structure calculation and interface reaction prediction of Al/Cu system[J]. Transactions of Materials and Heat Treatment, 2014, 35(8): 213.（蒋淑英， 李世春 . Al/Cu 系金属间化合物价电子结构计算与界面反应预测[J]. 材料热处理学报，2014, 35(8): 213.）
• [19] Zhong X P, Gao Y J, Liu H. Valence electronic structures of Al-Cu alloy in early aging condition[J]. The Chinese Journal of Nonferrous Metals, 2004, 14(1): 55.（钟夏平， 高英俊， 刘慧 . Al-Cu 合金时效初期的价电子结构[J]. 中国有色金属学报，2004, 14(1): 55.）
• [20] Gao Y J, Zhong X P, Liu H, Ban D M. Calculation on valence electron structures of metastable phase in Al-Cu alloy[J]. Chinese Journal of Rare Metals, 2003, 27(6): 845.（高英俊， 钟夏平， 刘慧， 班冬梅 . Al-Cu 合金亚稳相的价电子结构分析[J]. 稀有金属，2003, 27(6): 845.）
• [21] Gao Y J, Huang C G, Wang T C, Lan Z Q, Wei Y Y. Electron structure of θ（Al_2Cu） in Al-Cu alloy[J]. Function Materials, 2004, 35(s): 1103.（高英俊， 黄创高， 王态成， 蓝志强， 韦银燕 . Al-Cu 合金中θ相的价电子结构分析[J]. 功能材料，2004, 35(s): 1103.）
• [22] Qu H, Qi J X, Liu W D, Xu Q Z. Analysis of valence electron structure of the interface between Ω/Mg-Ag/α in Al-Cu-Mg-Ag alloy[J]. Rare Metal Materials and Engineering, 2020, 49(10): 3419.（屈 华， 齐健学， 刘伟东， 徐巧至 . Al-Cu-Mg-Ag 合金Ω/Mg-Ag/α界面价电子结构分析[J]. 稀有金属材料与工程，2020, 49(10): 3419.）
• [23] Qu H, Xu Q Z, Liu W D, Qi J X, Lou Q, Jiang X Y. Relationship between the valence electron structure of Ω and the ability of precipitation hardening in Al-Cu-Mg-Ag alloys[J]. Materials Reports, 2021, 35(12): 12110.（屈 华， 徐巧至， 刘伟东， 齐健学， 娄 琦， 蒋新宇 . Al-Cu-Mg-Ag 合金Ω相价电子结构与沉淀硬化能力的关系[J]. 材料导报，2021, 35(12): 12110.）
• [24] Qu H, Liu W D, Qi J X, Xu Q Z. Valence electron structure and aging sequence of solid solution in Al-Cu-Mg alloy with addition of Ag[J]. Chinese Journal of Rare Metals, 2020, 44(8): 792.（屈 华， 刘伟东， 齐健学， 徐巧至 . Ag 对 Al-Cu-Mg 合金固溶体价电子结构及时效惯序的影响[J]. 稀有金属，2020, 44(8): 792.）
• [25] Liu W D, Zhang X, Qu H. Valence electron structures of FeB and Fe_2B and hardening essence of boronizing layer of steel surface[J]. Materials Reports, 2018, 32(4): 672.（刘伟东， 张旭， 屈 华 . FeB 与 Fe_2B 价电子结构与钢表面渗硼层硬化本质[J]. 材料导报，2018, 32(4): 672.）
• [26] Liu W D, Liu Z L, Qu H. Calculation of valence electron structures in Alloying γ-TiAl and its mechanical properties[J]. Rare Metal Materials and Engineering, 2003, 32(11): 902.（刘伟东， 刘志林， 屈 华 . 合金γ-TiAl 价电子结构的计算及其力学性能[J]. 稀有金属材料与工程，2003, 32(11): 902.）
• [27] Kim K, Roy A, Gururajan M P, Wolverton C, Voorhees P W. First-principles/phase-field modeling of θ′precipitation in Al-Cu alloys[J]. Acta Materialia, 2017, 140: 344.
• [28] Zhou L, Wu C L, Xie P, Niu F J, Ming W Q, Du K, Chen J H. A hidden precipitation scenario of the θ′-phase in Al-Cu alloys[J]. Journal of Materials Science and Technology, 2021, 75: 126.
• [29] Bastow T J, Celotto S. Structure evolution in dilute Al(Cu) alloys observed by ~(63)Cu NMR[J]. Acta Materialia, 2003, 51: 4621.
• [30] Meetsma A, De Boer J L, Van Smaalen S. Refinement of the crystal structure of tetragonal Al_2Cu[J]. Journal of Solid State Chemistry, 1989, 83(2): 370.
• [31] Muddle B C, Polmear I J. The precipitate Ω phase in Al-CuMg-Ag alloys[J]. Acta Metallurgica, 1989, 37(3): 777.
• [32] Yang S L, Zhao X J, Chen H W, Wilson N, Nie J F. Atomic structure and evolution of a precursor phase of Ω precipitate in an Al-Cu-Mg-Ag alloy[J]. Acta Materialia, 2022, 225: 117538.