Solid solution strengthening of magnesium single crystals—I alloying behaviour in basal slipDurcissement des solutions solides de monocristaux de magnesium—i. influence d'une addition de solute sur le glissement de baseLegierungsverfestigung von magxesiumeinkristallen—I. legierungsverhalten bei basisgleitung
Abstract
Solution strengthening in single crystals of magnesium containing Zn in amounts up to 0.45 at. % has been investigated over the temperatures between 78°K and 423°K. The critical resolved shear stress for basal slip was found to increase with the square root of the solute concentration in two linear stages having a transition at 0.025 at. % Zn. No solution hardening was observed above 330°K when the solute content was less than 0.025 at. % Zn. Using transmission electron microscopy of thin foils the basal dislocation density has been found to increase linearly with the square root of the solute concentration. This increase however, could not account for the observed variation in the athermal component of the CRSS with alloying. The increase in the long range stress field can be best explained in the light of Fleischers friction stress mechanism. The rate theory has been used to identify the short range obstacles, and the low temperature solution hardening is discussed.
Résumé
L'effet d'une addition de zinc (jusqu'à 0,45% at. de Zn) sur la consolidation de monocristaux de magnésium a été étudié entre 78°K et 423°K. Les auteurs ont trouvé que la cission critique résolue pour le glissement de base augmente avec la racine carrée de la concentration en soluté suivant deux stades linéaires ayant une transition à 0,025 % at. de Zn. L'addition de soluté n'entraîne pas de durcissement au-dessus de 330°K. si la concentration en soluté est inférieure à 0,025 % at. Zn. En utilisant la microscopie électronique par transmission sur des feuilles minces, les auteurs ont trouvé que la densité des dislocations de base augmente linéairement avec la racine carrée de la concentration en soluté. Cette augmentation ne peut cependant pas expliquer la variation qui a été observée pour la composante athermique de la cission critique par addition du soluté. L'augmentation dans le domaine des contraintes à longue distance peut être expliquée clairement à l'aide du mécanisme de frottement interne de Fleischer. La théorie de la vitesse a été utilisée pour identifier les obstacles à courte distance, et les auteurs discutent la consolidation de la solution à basse température.
Zusammenfassung
Die Legierungsverfestigung in Mg-Zn-Einkristallen mit einem Zinkgehalt bis zu 0,45 At. % wurde im Temperaturbereich zwischen 78°K und 423°K untersucht. Die kritische Schubspannung für Basisgleitung nahm mit der Wurzel aus der Zn-Konzentration in zwei linearen Stufen mit einem Übergang bei 0,025 At. % Zn zu. Bei Fremdstoffgehalten von weniger als 0,025 At. % wurde oberhalb 330°K keine Legierungsverfestigung beobachtet. Die elektronenmikroskopische Untersuchung dünner Folien zeigte, daβ die Versetzungsdichte in der Basisebene mit der Wurzel aus der Fremdstoffkonzentratiori zunahm. Diese Zunahme konnte jedoch nicht die bei Zulegierung beobachtete Änderung der athermischen Komponente der kritischen Schubspannung erklären. Die Zunahme des weitreichenden Spannungsfeldes kann am besten an Hand des Fleischer-Mechanismus erklärt werden. Die Hindernisse kurzer Reichweite wurden mit Hilfe der “'rate theorz” identifiziert; die Legiorungsverfestigung bei tiefen Temperaturen wird diskutiert.
References (25)
- A.I. Goss et al.
Acta Met.
(1956) - D. Hardie et al.
Phil. May.
(1959) - H. Scharf et al.
Z. Metallk
(1967) - A.A. Hendrickson et al.
Trans. Arn. Inst. Min. Engrs
(1961) - A. Seeger
Phil. Mag.
(1955) - A. Akhtar et al.
- E.S. Levine et al.
Trans. Am. Inst. Min. Engrs
(1959) - H. Conrad
High Strength Materials
- A. Seeger
- W.A. Tiller
J. appl. Phys.
(1958)
Phil. Mag.
Trans. Am. Inst. Min. Engrs
Cited by (307)
The investigation on microstructure evolution and mechanical behavior of extruded Mg-1.5Al-xLa-Mn (x=0.5, 1, 2wt%) alloys
2024, Materials Today CommunicationsIn this study, the microstructure evolution and mechanical behaviour of Mg-1.5Al-xwt%La-Mn (ALaM-x) (x = 0.5, 1, and 2) alloys with low-cost were investigated. Microstructure analysis of the cast alloys revealed that the Al11La3 was preferentially precipitated, followed by Al2La, and finally Mg12La, as the Al/La ratio decreased. Nonetheless, the main precipitated phase in the alloy was Al11La3 phase, and it gradually coarsened and the content increased, with the increase of La content. The fine rod-like Al11La3 was broken and refined after extrusion, while the coarse Al11La3 was not completely broken, and aggregated unevenly within Mg matrix. As a result, the grain size of the alloys gradually increased, and the strength gradually decreased. When adding 0.5 wt%La, compared with pure Mg, the ALaM-0.5 alloy exhibited finer grain microstructure with an average size of 1.83 μm and a grain refinement rate of 90%; the corresponding tensile yield strength (TYS) and ultimate tensile strength (UTS) are 262.5±3.0 MPa and 275.0±2.4 MPa, with an increase rate of 124.7% and 52.1%, respectively. The calculation and analysis of strengthening mechanism showed that the high strength of the alloy was mainly attributed to fine-grained strengthening with an accounting for up to 42%. Besides, the inverse relationship between the square root of the reciprocal of grain size (d−1/2) and strain hardening exponents (n) was found in this study, and the precipitates were found to delay the weakening trend of strain hardening capacity with decreasing grain size.
Ductility enhancement by activating non-basal slip in Mg alloys with micro-Mn
2024, Transactions of Nonferrous Metals Society of China (English Edition)The effect of micro-Mn addition on the microstructure and mechanical properties of Mg alloys was analyzed. Electron back scattered diffraction, slip traces analysis, transmission electron microscopy and visco-plastic self-consistent polycrystal constitutive modeling were performed to investigate the deformation mechanisms in the tensile test. The results show that the average grain size of Mg−Mn alloys decreases from 28.30 to 5.10 μm with Mn addition. Furthermore, with the increment of Mn content, the ductility of the as-extruded samples improves from 14.33% to 20.33%, and the yield strength increases from 84 to 180 MPa. The reason for this simultaneous improvement is that the critical resolved shear stress gap between basal slip and non-basal slip decreases from 173 to 115 MPa, which leads to the increase of non-basal slip activity. The adjustment of slip system difference by microalloying elements provides a way to develop Mg alloys with high strength and ductility.
Exceptional improvement in the yield strength of AZ61 magnesium alloy via cryo-stretching and its implications on the grain growth during annealing
2024, Journal of Alloys and CompoundsThis study explored the influence of pre-stretching temperature on the microstructural characteristics and deformation behavior of AZ61 magnesium alloy and its implications on grain growth during subsequent annealing. AZ61 alloy was stretched to 5% plastic strain along rolling (RD) and transverse direction (TD) at room (RT) and cryogenic temperature (−150 °C, CT) followed by annealing at 320 °C for 1 h to investigate the twinning and dislocation evolution and its consequent effect on the flow stress, plastic strain and strain hardening rate. Compared to RT-stretched samples, significant improvement in yield stress, strain hardening rate and moderate reduction in elongation to failure were witnessed for CT-stretched samples along RD and TD. The subsequent EBSD analysis revealed the increased fraction of fine {10−12} twins and nucleation of multiple {10−12} twin variants caused by higher local stress concentration at the grain boundaries in CT-stretched samples as manifested by the kernel average misorientation. This higher twin fraction and twin-twin interaction imposed the strengthening by restricting the mean free path of dislocations leading to higher flow stress and strain hardening rate. During annealing of the RT/CT-stretched samples, the residual strain energy and twin boundaries were decreased due to static recovery leading to a coarse-grained twin-free microstructure. Strain induced boundary migration (SIBM) was found to be the predominant mechanism governing the grain growth during annealing via movement of high angle grain boundaries.
Analytical model for estimating calcium solution strengthening in single-crystal Mg-Ca alloys at finite temperatures
2023, MaterialiaMg is the lightest structural metal and a suitable replacement for heavy steel and Al alloys. However, Mg exhibits poor plastic formability at room temperature, and the strength of conventional Mg alloys is less than that of most Al alloys. Its low formability at room temperature is attributed to the lack of slip systems because of the extremely large gap in the critical resolved shear stress (CRSS) between the lowest basal system and the other slip and twin systems. This low CRSS of the basal slip usually limits the strength of Mg alloys. Therefore, strengthening the basal slip is important to improve the strength and deformability of Mg alloys and enhance their ductility. In this study, we construct an analytical model for predicting the CRSS in single-crystal Mg–Ca alloys at finite temperatures by quantitatively investigating the CRSS for the 〈a〉 dislocation gliding on the basal plane at temperatures from 1 to 500 K through molecular-dynamics computations. The prediction results agree well with our simulation results and the micropillar compression test results of Mg–0.3at.%Ca and Mg–0.6at.%Ca alloys at room temperature.
Recent research advances in Mg single crystal based on the crystal orientations：A review
2023, Journal of Materials Research and TechnologyDue to the hexagonal close-packed (HCP) crystal structure of Mg, the plasticity is poor at low temperatures. In order to solve this problem, the in-depth researches on various deformation modes of Mg are very necessary. However, there are many limitations to study these deformation modes in Mg polycrystals owing to the effect of grain boundaries, etc. It is more reasonable to conduct the researches in Mg single crystals, especially investigating the influence of crystal orientations, and the advantages of Mg single crystals are prominent particularly. On this basis, various investigations in Mg single crystals are carried out thoroughly in recent years, such as the critical resolved shear stress (CRSS) calculation, the slip and twinning modes activation determining, recrystallization behaviors and so on. In order to make clear the research advantages in Mg single crystals, a critical brief summary is conducted in this paper. Besides, various crystal plasticity finite element modeling (CPFEM) and electrochemical corrosion used in Mg single crystals are also reviewed. Finally, the current challenges and possible research directions are proposed.
Implications of twinning on the microstructure development, crystallographic texture and mechanical performance of Mg alloys- a critical review
2023, Journal of Magnesium and AlloysDeformation twinning is profusely activated in the Mg alloys due to lower critical resolved shear stress (CRSS) compared to the non-basal slip systems (prismatic <a> and pyramidal <c + a>) and plays a significant role in texture reorientation, grain refinement and enhancement of mechanical performance. Twinning is a sequential process comprising twin nucleation, twin propagation and twin growth, hence several intrinsic and extrinsic parameters that facilitate or suppress the process have been critically reviewed. The dependence of twinning on the grain size, deformation temperature, favorable grain orientation and shear strain have been thoroughly discussed in the context of published literature and an attempt has been made to provide a benchmark conclusive finding based on the majority of works. Furthermore, the subsequent effect of twinning on the mechanical performance of Mg alloys, including ductility, formability and tension-compression asymmetry has been discussed in detail. Lastly, the stability of twins, including stress and thermal stability, is summarized and critical issues related to pertinent bottlenecks have been addressed.