Strain Field and Dynamics Around S-Phase in 2324 Aluminum Alloy AITranslate

［1］Ramezanali F，Hamed J A，Roohollah J，Zuzana H，Štefan N. Effects of pre-and post-friction surfacing heat treatment on microstructure and corrosion behavior of nickel-aluminide reinforced Al-Cu-Mg alloy ［J］. Journal of Alloys and Compounds，2022，906：164211.

［2］（宋赵熙，李元东，刘文憬，杨昊坤，曹杨婧，毕广利. La元素对铸造Al-4.8Cu合金力学和导热性能的影响 ［J］. 稀有金属，2024，48（6）：786.）

Z X Song，Y D Li，W J Liu，H K Yang，Y J Cao，G L Bi. Thermal conductivity and mechanical properties of casting Al-4.8Cu alloy with addition of La ［J］. Chinese Journal of Rare Metals，2024，48（6）：786.

［3］Bo G W，Wang Y L，Liu M C，Tang J，Jiang F L，Teng J，Xiao G，Fu D F，Zhang H. Experimental and modeling investigations of the non-isothermal and isothermal precipitations in an Al-Cu-Mg-Zr alloy with various pre-precipitation microstructures ［J］. Materials & Design，2022，217：110640.

［4］（王强，张炜. 喷丸成形弹坑尺寸对2324铝合金疲劳性能的影响 ［J］. 中国表面工程，2020，33（1）：18.）

Q Wang，W Zhang. Effect of crater size in shot peening on fatigue properties of 2324 aluminum alloy ［J］. China Surface Engineering，2020，33（1）：18.

［5］（刘俊涛，张义，刘君城，冉凡青，崔莉. 浅析2324铝合金铸态组织及均匀化处理 ［J］. 中国高新技术企业，2016，（24）：64.）

J T Liu，Y Zhang，J C Liu，F Q Ran，L Cui. Analysis of as cast structure and homogenization treatment of 2324 aluminum alloy ［J］. China High-Tech Enterprises，2016，（24）：64.

［6］Zhang P，Liu Z H，Zhang J L，Yu J，Mai Q Q，Yue X J. Effect of aging plus cryogenic treatment on the machinability of 7075 aluminum alloy ［J］. Vacuum，2022，208：111692.

［7］Wang Z X，Li M Y，Han Q H，Yun X，Zhou K，Gardner L，Mazzolani F M. Structural fire behaviour of aluminium alloy structures：review and outlook ［J］. Engineering Structures，2022，268：114746.

［8］Perlitz H. Crystal structure of β-aluminium-magnesium alloy ［J］. Nature，1944，154：606.

［9］Wolverton C. Crystal structure and stability of complex precipitate phases in Al-Cu-Mg-（Si） and Al-Zn-Mg alloys ［J］. Acta Materialia，2001，49（16）：3129.

［10］Kovarik L，Miller M K，Court S A，Mills M J. Origin of the modified orientation relationship for S （S″）-phase in Al-Mg-Cu alloys ［J］. Acta materialia，2006，54（7）：1731.

［11］Hu Z Y，Fan C H，Shen T，Ou L，Dai N S，Wang L. Effect of aging treatment on evolution of S′ phase in rapid cold punched Al-Cu-Mg alloy ［J］. Transactions of Nonferrous Metals Society of China，2021，31（7）：1930.

［12］（张锰，郑超，王浩军，吉丽. 预拉伸变形对2024铝合金再结晶组织与性能的影响 ［J］. 锻压技术，2025，50（6）：58.）

M Zhang，C Zheng，H J Wang，L Ji. The influence of pre-straining deformation on recrystallization structure and properties of 2024 aluminum alloy ［J］. Forging Technology，2025，50（6）：58.

［13］（乔及森，李一佳，张晓波，李琦伦. 反向挤压双金属铝合金复合管材制备及其微观组织演化分析 ［J］.  塑性工程学报，2025，32（1）：49.）

J S Qiao，Y J Li，X B Zhang，Q L Li. Preparation of reverse extrusion double-metallic aluminum alloy composite tubing and analysis of its microstructure evolution ［J］. Journal of Plasticity Engineering，2025，32（1）：49.

［14］Huang C C，Qi L，Chen J Q，Guan R G，Ojo O A，Wang Z G. Effect of TiC nanoparticles on the hot deformation behavior of AA7075 aluminum alloy ［J］. Materials Characterization，2021，181：111508.

［15］Radmilovic V，Kilaas R，Dahmen U，Shiflet G J. Structure and morphology of S-phase precipitates in aluminum ［J］. Acta Materialia，1999，47（15-16）：3987.

［16］Feng Z Q，Yang Y Q，Huang B，Han M，Luo X，Ru J. Precipitation process along dislocations in Al-Cu-Mg alloy during artificial aging ［J］. Materials Science and Engineering：A，2010，528（2）：706.

［17］（林成，曹丽云，曹力生，张春刚. Al-Cu合金GPI区中应变场及Cu成分的价电子结构分析 ［J］. 稀有金属，2012，36（6）：1010.）

C Lin，L Y Cao，L S Cao，C G Zhang. Valence electron structure analysis of strain field and Cu composition in GPI region of Al-Cu alloy ［J］. Chinese Journal of Rare Metals，2012，36（6）：1010.

［18］（侯小虎，白朴存，赵春旺，邢永明. 喷射沉积Al-Zn-Mg-Cu合金GP区应变场的定量测试 ［J］. 实验力学，2011，26（1）：16.）

X H Hou，P C Bai，C W Zhao，Y M Xing. Quantitative test of strain field in GP region of Al-Zn-Mg-Cu alloy by jet deposition ［J］. Experimental Mechanics，2011，26（1）：16.

［19］（赵倩，袁晓光，黄宏军，赵鹏. Al-Mg-Si-Zr-XEr合金β″相析出动力学研究 ［J］. 稀有金属材料与工程，2016，45（11）：2889.）

Q Zhao，X G Yuan，H J Huang，P Zhao. Precipitation kinetics for β″ phase of Al-Mg-Si-Zr-XEr alloys ［J］.  Rare Metal Materials and Engineering，2016，45（11）：2889.）

［20］Khalfallah A，Raho A A，Amzert S，Djemli A. Precipitation kinetics of GP zones，metastable η′ phase and equilibrium η phase in Al-5.46wt.%Zn-1.67wt.%Mg alloy ［J］. Transactions of Nonferrous Metals Society of China，2019，29（2）：233.

［21］Hytch M J，Snoeck E，Kilaas R. Quantitative measurement of displacement and strain fields from HREM micrographs ［J］. Ultramicroscopy，1998，74：3.

［22］Yan S L，Yang H，Li H W，Yao X. Variation of strain rate sensitivity of an aluminum alloy in a wide strain rate range：mechanism analysis and modeling ［J］. Journal of Alloys and Compounds，2016，688：776.

［23］Vyazovkin S. Kissinger method in kinetics of materials：things to beware and be aware of ［J］. Molecules，2020，25（12）：2813.

［24］Mourad I D，Abdelhafid T，Abdelkrim R，Chihaoui Y. The determination of the activation energy varying with the precipitated fraction of β″ metastable phase in an Al-Si-Mg alloy using non-isothermal dilatometry ［J］. Thermochimica Acta，2014，577：5.

［25］Charai A，Walther T，Alfonso C，Zahra A M，Zahra C Y. Coexistence of clusters，GPB zones，S″-，S′- and S-phases in an Al-0.9%Cu-1.4%Mg alloy ［J］. Acta Materialia，2000，48（10）：2751.

Basic Information:

DOI：10.13373/j.cnki.cjrm.XY22120011

Chinese Library Classification Number:TF803.21

Citation Information:

Aluminum alloys are widely appliedd in the aerospace industry due to their excellent mechanical properties, superior corrosion resistance, good machinability, high strength to density ratio, and desirable electrical and thermal conductivity. So far, the aluminization application ratio of civil aircraft exceeds 70%, while that of military aircraft is more than 48%. Among them, the second series of aluminum alloys （Al, Cu, Mg）, as heat-treatable strengthend aluminum alloys, have excellent mechanical properties. Therefore, they are widly used as aircraft structural materials. In recent years, 2324 aluminum alloy has been optimized by regulating the content of alloying elements and optimizing heat treatment processes, endowing it with excellent mechanical properties. After aging treatment, the second phases mainly include S', S and T phases. It is notable that S phase acts as the main strengthening phase at room temperature for 2324 aluminum alloy. T phase is the high-temperature strengthening phase, which is a brittle phase at room temperature and there by deteriorates the comprehensive performance of the alloy. In-depth researchon S-phase can help to improve the performance of 2324 aluminum alloy. In this paper, the strain field and nucleation process around S-phase in 2324 aluminum alloy were systematically studied. With transmission electron microscopy （TEM） and differential scanning calorimetry （DSC）, the strain field and nucleation kinetics around S-phase during aging were investigated. The strain field around S-phase and its intrinsic characteristics were revealed, and the relationship between activation energy and transformation fraction, as well as nucleation mechanism of S-phase, were elucidated. The results showed that a strong stress field existed around the early-formed S-phase, and the stress magnitude decreased with the increasing distance from S-phase. The size of S-phase also affected the surrounding stress field, and the smaller the width of S-phase, the higher the surrounding stress field. On the one hand, S-phase was incoherent with the alloy matrix, the lattice mismatch between the two phases induced the formation of a stress field. The calculated lattice mismatch were –1.25%, 1.92%, and –1.45% for ［100］_S//［100］_Al, ［010］_S//［012］_Al, ［001］_S//［021］_Al, respectively. On the other hand, there were diffused Cu/Mg atoms around S phase, and the concentration of diffused atoms was distributed in a gradient along the direction away from S-phase. In general, the concentration of Cu/Mg atoms was high in the region close to S-phase and low in the region far away from it. Since the atomic sizes of Cu and Mg atoms differed greatly from that of the aluminum atoms of the matrix, a stress field was formed around S-phase. In summary, the stress field around S-phase resulted fromthe superposition of two contributions：the stress field generated by the lattice mismatch and Cu/Mg solute atoms. Moreover, all characteristic temperatures of S'-phase increased with rising heating rate, indicating that the formation and dissolution of S' and S-phase were controlled by the reaction kinetics and exhibited thermal activation characteristics. In addition, the magnitude of precipitation decreased as the increase of the heating rate, which could be explained by the enhanced solid solubility of Cu at a higher heating rates. The average values of the activation energies for the precipitation of S' and S-phases calculated by Kissinger method were 76.65 and 119.57 kJ·mol⁻¹, respectively, and corresponded to vacancy migration energies of 41 and 66.9 kJ·mol⁻¹ in Al-Cu-Mg alloy, respectively. Therefore, the precipitation of S' and S phases was governed by multiple factors rather thanmerley the diffusion of Cu atoms. Then, as the heating rate increased, the temperature was higher for the transformation fraction, indicating that the transformation degree increased with the rising heating rate and temperature. These features could be explained from two aspects：1） at a certain heating rate, the diffusion of solute atoms was enhanced with increasing temperature, thereby promoting the transformation； 2） at a fixed temperature, as the heating rate decreased, the solute atoms had enough time to diffuse, thus increasing the transformation fraction. The apparent activation energies E calculated by the Analytical method were 84.98 and 148.53 kJ·mol⁻¹ for S and S' phases, respectively. The activation energy required for S'-phase formation decreased with the increase of transformation fraction, and the activation energy during the formation of S-phase increases with the increase of the conversion rate. The decreasing activation energy of S'-phase was due to the gradual increase in the nucleation sites during aging. The increase in S-phase activation energy was due to the decrease in alloying elements and dislocations in the matrix with prolonged aging, making the nucleation of S-phase increasingly difficult and requiring higher activation energy. In conclusion, the activation energy of S'-phase decreased with the increase of the transformation fraction, and the activation energy of S-phase increased with the increase of the transformation fraction.