Rolled Magnesium Alloy Research Articles

Amplitude Dependent Internal Friction in a Mg-Al-Zn Alloy Studied after Thermal and Mechanical Treatment

The amplitude-dependent internal friction of continuously-cast and rolled AZ31 magnesium alloy was measured in this study. Samples were annealed and quenched step by step; immediately after the treatment, the amplitude dependence of the logarithmic decrement was measured. Changes in the microstructure due to thermomechanical treatment were reflected in changes in the damping. Internal friction is influenced by the dislocation substructure and its modification due to solute atoms migration, microplastic deformation, and twins’ formation. Internal friction in the rolled sheets is affected by the rolling texture.

Prediction for Magnesium Alloy Rolling Force Based on Quantitative Study of Contact Friction

The magnesium alloy hot rolling process was investigated. A method was proposed to determine the friction factor in the process through the comparative analysis of finite element analysis result and experimental data. Mathematical model for solving the friction factor was established, combining with multi-parameters of the rolling process: rolling temperature, rolling speed and reduction rate. Based on calculation model of rolling force and temperature distribution along the contact region in hot rolling of AZ31B magnesium alloy in previous researches, to the rolling force prediction model was optimized and reconstructed considering the normal pressure and friction stress comprehensively. The contact friction stress and its influence on rolling force with an approximate percentage of 4.36% was defined.

Effect of Ti Addition on Corrosion Properties of As-Cast and Hot-Rolled AM60 Magnesium Alloys

This study investigates the effect of Ti addition (0, 0.2, 0.5, 1wt%) on corrosion resistance of as-cast and hot rolled AM60 magnesium alloy. Corrosion behaviors were investigated by immersion tests and electrochemical analysis. The results showed that Ti addition altered the microstructure of as-cast AM60 magnesium alloy by decreasing the amount of β-Mg17Al12 eutectic phase. Homogenization treatment resulted in the dissolution of the most of the β-Mg17Al12 phases. Homogenized samples exhibited the lowest corrosion rate in immersion test while the best corrosion resistance was found for hot-rolled samples in electrochemical test. In hot-rolled state, Ti addition led to a slight change in the corrosion resistance of AM60 magnesium alloy.

Effect of Sn Addition on Corrosion Properties of As-Cast and Hot-Rolled AZ31 Magnesium Alloys

In this study, the effect of Sn addition on corrosion resistance of as-cast and hot rolled AZ31 magnesium alloy was investigated. Sn additions were made by 0.2 wt%, 0.5 wt% and 1 wt%. An electric resistance furnace was used to produce alloys. Hot rolling process was performed at 350 °C by 40% thickness reduction at one rolling pass. Microstructure characterizations were performed by optical (OM) and scanning electron microscope (SEM). Immersion tests and electrochemical analyses were performed to investigate the corrosion resistance of the alloys. A 3.5% NaCl working solution at room temperature was used in both corrosion tests. The results showed that Sn addition decreased the primary dentrite size and restricted the growth of secondary dentritic arm. The as-cast structures transformed to dynamically recrystallized grain structures after hot-rolling process in all the alloys. Corrosion resistance of AZ31 magnesium alloy tended to decrease with Sn addition. This decrease was more clear in homogenized and hot-rolled states while there were some flactuations in as-cast states.

Simultaneous multiscale measurements on dynamic deformation of a magnesium alloy with synchrotron x-ray imaging and diffraction

Dynamic split Hopkinson pressure bar experiments with in situ synchrotron x-ray imaging and diffraction are conducted on a rolled magnesium alloy at high strain rates of ~5500s−1. High speed multiscale measurements including stress–strain curves (macroscale), strain fields (mesoscale), and diffraction patterns (microscale) are obtained simultaneously, revealing strong anisotropy in deformation across different length scales. {101¯2} extension twinning induces homogenized strain fields and gives rise to rapid increase in strain hardening rate, while dislocation motion leads to inhomogeneous deformation and a decrease in strain hardening rate. During the early stage of plastic deformation, twinning is dominant in dynamic compression, while dislocation motion prevails in quasi-static loading, manifesting a strain-rate dependence of deformation.

Microstructure and Properties of Rolled Magnesium Alloy Thick Plate at Different Positions

The microstructure and properties of rolled AZ31 magnesium alloy sheet with the change of normal position were investigated by electronic universal testing machine, ZEISS optical microscopy and scanning electron microscopy. The tensile test results showed that the mechanical properties of sample selected at the depth of 8mm, which is 2/5 of the whole thickness counting from rolling plane are closest to the properties for whole sheet. Microstructure characterization indicated that a large number of tiny grains are distributed around the large grains. The majority of these grains are equiaxed grains, and the few twins could be observeded. The fracture mechanism was ascribed to mixed ductile and brittle fractures.

Multiscale measurements on temperature-dependent deformation of a textured magnesium alloy with synchrotron x-ray imaging and diffraction

In situ synchrotron x-ray imaging and diffraction are used to investigate deformation of a rolled magnesium alloy under uniaxial compression at room and elevated temperatures along two different directions. The loading axis (LA) is either perpendicular or parallel to the normal direction, and these two cases are referred to as LA⊥〈c〉 and LA∥〈c〉 loading, respectively. Multiscale measurements including stress–strain curves (macroscale), strain fields (mesoscale), and diffraction patterns (microscale) are obtained simultaneously. Due to initial texture, {101¯2} extension twinning is predominant in the LA⊥〈c〉 loading, while dislocation motion prevails in the LA∥〈c〉 loading. With increasing temperature, fewer {101¯2} extension twins are activated in the LA⊥〈c〉 samples, giving rise to reduced strain homogenization, while pyramidal 〈c+a〉 slip becomes readily activated, leading to more homogeneous deformation for the LA∥〈c〉 loading. The difference in the strain hardening rates is attributed to that in strain field homogenization for these two loading directions.

Development of Room Temperature Formability of Rolled Magnesium Alloy Sheets by Texture Control

Development of Room Temperature Formability of Rolled Magnesium Alloy Sheets by Texture Control

Polarization characteristics of rolled AZ31 magnesium alloy in simulated body environment

Polarization characteristics of rolled AZ31 magnesium alloy in simulated body environment

Modeling the deformation behavior of a rolled Mg alloy with the EVPSC-TDT model

Magnesium and its alloys are characterized by a strong basal texture, resulting in severe anisotropy at low temperature. To investigate the deformation behavior of a rolled magnesium alloy AZ31 at room temperature, uniaxial compression and tension experiments along four directions were performed and modeled using both the EVPSC-TDT and the VPSC-TDT models. The required threshold stress parameters were determined by curve fitting. Similar parameters were found to fit relatively well for all the experimental flow curves for both models. The predictions of the two models are also very similar beyond the elastic strain. The simulations reveal only a very limited increase with strain of the threshold stress for basal slip, which is favorable for basal texture development, whereas the threshold stresses for other deformation modes increase significantly. A discrepancy between experiments and simulations suggests that depending on loading condition strain accommodation between grains by basal slip varies in ease. A deformation-path dependent discrepancy between the modeled stress and the experimental curves is also found for the threshold stress for {10−12} twinning. This discrepancy is assumed to be related to the larger number of twin variants activated in tension as compared to compression, due to twin boundary hardening. A {10−12} twin-associated hardening, primarily on pyramidal slip and prismatic slip systems, evaluated to be about 15MPa for both through thickness tension and in-plane compression, is included in the model via the use of a higher latent hardening modulus these slip systems by twinning.

Effects of pre-tension on fatigue behavior of rolled magnesium alloy

The effects of pre-tension on the fatigue properties of a rolled Mg-3Al-1Zn (AZ31) alloy were investigated by imposing 2%, 5%, and 10% tensile strains along the rolling direction before low-cycle fatigue tests. The investigation showed that the applied pre-tension increased the dislocation density and introduced a small number of twins into the material. Although the as-rolled sample and all the pre-tensioned samples exhibited asymmetric hysteresis loops owing to the alternation of twinning and detwinning during each cycle, the tensile and compressive peak stresses increased with an increase in the amount of pre-tension during the first cycle. With an increase in the number of cycles, however, the flow stress, mean stress, plastic strain energy density, and hysteresis loop of the samples became similar irrespective of the amount of pre-tension, which is attributed to cyclic strain softening or hardening behavior depending on the initial dislocation density. Despite the relatively large pre-deformation, the pre-tensioned samples exhibited a fatigue life equivalent to that of the as-rolled sample because of an early extinction of the difference in the cyclic stress-strain response caused by pre-tension. This result demonstrates that the pre-tension process can improve the yield strength of rolled Mg alloys without a loss of their low-cycle fatigue resistance.

Effect of initial twins on the stress-controlled fatigue behavior of rolled magnesium alloy

The effect of initial twins on the fatigue behavior of rolled AZ31 alloy was investigated by introducing {10–12} twins into the alloy through pre-deformation and then conducting fully reversed stress-controlled fatigue tests along the rolling direction (RD) and the direction normal to the rolling plane (ND). It was found that the fatigue life of the alloy is higher under RD loading than under ND loading, but when initial twins exist, the fatigue resistance along the RD decreases, whereas the ND fatigue resistance increases, eventually reversing the fatigue resistance behavior under the ND and RD loading conditions. The tensile mean strain generated under ND loading is also changed to compressive strain by initial twins, whereas the reverse is true under RD loading. The fatigue strength of samples with and without twins is inversely proportional to the logarithm of their plastic strain energy density, which corresponds to the inner area of the hysteresis loop at half-life, irrespective of the loading direction.

Mechanical Behavior and Microstructure Evolution of a Rolled Magnesium Alloy AZ31B Under Low Stress Triaxiality

Plastic deformation up to final rupture failure of a rolled magnesium (Mg) alloy Mg–3.0Al–1.0Zn–0.34Mn (AZ31B) under low stress triaxiality was investigated. Local strain evolution was quantified by the digital image correlation (DIC) technique analysis with tensile, combined tensile-shear, and shear specimens, corresponding to the stress triaxiality of 1/3, 1/6 and 0, respectively. Stress–strain curves show that the yield stress reduces with the decrease in the stress triaxiality, and obviously exhibits different strain hardening response. Electron backscatter diffraction (EBSD) observations reveal that the twinning behavior depends on stress triaxiality. Before fracture, double twinning is the dominant mechanism at the stress triaxiality of 1/3, while extension twinning is prevalent at the stress triaxiality of 0. Moreover, scanning electron microscopy (SEM) shows that the fracture mechanism is transformed from micro-void growth and coalescence to internal void shearing as the stress triaxiality decreases from 1/3 to 0.

Microstructure, texture and mechanical properties of hot-rolled Mg–4Al–2Sn–0.5Y–0.4Nd alloy

Abstract A new Mg–Al–Sn–RE alloy with high ductility at room temperature has been developed. Homogenized Mg–4Al–2Sn–0.5Y–0.4Nd plates 25 mm in thickness were hot-rolled to 1 mm at 673K. The microstructures were characterized as fully recrystallized grains with a lot of fragmented fine particles along the rolling direction. The sheet specimen possesses basal texture of (0002) with the basal pole tilting by about 15° from the normal direction toward the rolling direction. Meanwhile, the texture strength was weakened, which is resulted from the non-basal slip and recrystallization texture. For the as-rolled alloy, the yield strength and tensile strength in transverse direction are both higher than those of rolling direction. The average Lankford value is 1.83, which is lower than conventional AZ31 rolled magnesium alloy sheets. The relatively high elongation and low planar anisotropy implies good formability at room temperature.

Investigation of deformation twinning under complex stress states in a rolled magnesium alloy

A specially designed semi-circular notch specimen was employed in the current study to generate the various strain conditions, including uniaxial, biaxial, shear, and plane strains, which was utilized to explore the evolution of different deformation twinning systems under complex loading conditions. Using in situ synchrotron X-ray diffraction mapping method, it was found that the extensive double twins were activated during loading, while nearly no extension twinning activity was detected. After the formation of {10.1} and {10.3} compression twins, they transformed into {10.1}–{10.2} and {10.3}–{10.2} double twins instantaneously at the early stage of deformation. The lattice strain evolutions in different hkls were mapped at selected load levels during the loading-unloading sequence. The relationship between the macroscopic straining and microscopic response was established.

Modelling the Temperature Evolution During Hot Reversing Strip Rolling of Magnesium Alloys

The paper proposes the approach for the thermal through process modelling of the strip hot rolling chain of magnesium alloys. This strip hot rolling chain comprises the coil reheating after the Twin-Roll Casting (TRC) process, storage or transport operations and reversing hot rolling. The modelling of reversing rolling is implemented in connection with the simultaneous un-/coiling process of a coil. The numerical calculation is based on an object-oriented FEM tool kit written in MATLAB™ and is carried out in three spatial dimensions and time.

Substitution of Rare Earth Elements in Hot Rolled Magnesium Alloys with Improved Mechanical Properties

Magnesium alloys containing rare earth elements offer excellent strength at room temperature as well as at elevated temperatures and are distinguished by a high ignition-resistance. However, with regard to cost efficiency and the conversation of resources, these alloys are not suitable for commercial industrial applications. Therefore, the research project SubSEEMag at the Institute of Metal Forming/Technische Universität Bergakademie Freiberg focusses on the development of alternative alloy compositions, which meet the requirements on materials properties of magnesium alloys for industrial applications and production costs. Several magnesium alloys containing zinc, aluminum, manganese and calcium were poured in cylindrical molds at the Helmholtz-Zentrum Geesthacht. The characterization of the as-cast condition was carried out by light and scanning electron microscopy. Phase compositions were determined using EDX analysis. The Mg alloys were homogenized at different temperatures. Afterwards, hot rolling to a final thickness of 2.7 mm was conducted. The influence of temperature and time of the annealing on the microstructure and the mechanical properties of the hot rolled condition have been investigated. The results were discussed in comparison to commercial available Mg-RE alloys.

Deformation behavior upon two-step loading in a magnesium alloy sheet

Two-step loading tests were performed on an AZ31 rolled magnesium alloy sheet with strong basal texture in the normal direction, and the deformation behavior such as a stress–strain curve, Lankford value, and texture evolution was investigated both experimentally and numerically. When the sheet was subjected to compression in the rolling direction followed by tension in different directions, the following characteristic deformation was observed during the second loading: The sigmoidal shape of the stress–strain curve was more pronounced when the sheet was stretched in the rolling direction but less pronounced as the loading direction approached the transverse direction. The Lankford value during the second loading was much smaller than that of the virgin sheet. Observation of the microstructure showed that the detwinning activity during the second loading decreased as the loading direction approached the transverse direction. The aforementioned deformation behavior was qualitatively well predicted using a crystal-plasticity finite-element method. The crystal-plasticity analysis was then used to investigate the underlying deformation mechanism upon two-step loading, focusing especially on the effect of twinning and detwinning activities.

Low-energy, Mobile Grain Boundaries in Magnesium

The strong basal texture that is commonly developed during the rolling of magnesium alloy and can even increase during annealing motivates atomic-level study of dislocation structures of both <0001> tilt and twist grain boundaries (GBs) in Magnesium. Both symmetrical tilt and twist GBs over the entire range of rotation angles θ between 0° and 60° are found to have an ordered atomic structure and can be described with grain boundary dislocation models. In particular, 30° tilt and twist GBs are corresponding to energy minima. The 30° tilt GB is characterized with an array of Shockley partial dislocations bp:-bp on every basal plane and the 30° twist GB is characterized with a stacking faulted structure. More interesting, molecular dynamics simulations explored that both 30° tilt and twist GBs are highly mobile associated with collective glide of Shockley partial dislocations. This could be responsible for the formation of the strong basal texture and a significant number of 30° misorientation GBs in Mg alloy during grain growth.

AZ31Mg合金圧延材における引張および圧縮変形中のミクロ組織変化の観察

AZ31Mg合金圧延材における引張および圧縮変形中のミクロ組織変化の観察