Number Of Second-phase Particles Research Articles

Understanding the recrystallization kinetics in aluminium alloy billets with poorly developed cast structure

The paper describes the study of structure evolvement in A0 aluminum and 8011 and 8006 aluminum alloy billets with a low degree of the cast structure working when rolled at 300–500 °C and 3–8 s–1 strain rate. The grain structure was studied by optical microscopy with Axiovert 40 MAT microscope, intermetallic particles analysis was made using JEOL 6390A scanning electron microscope. Grain structure analysis showed that a dendritic structure gradually stretching in the direction of strain is observed in the cast state. Review of the effect of deformation modes and subsequent annealing on the grain structure helped obtain analytic equation to describe recrystallization kinetics. The effect of the Zener-Hollomon parameter value on recrystallization kinetics during subsequent annealing was demonstrated. It was established that at this stage of thermomechanical processing recrystallization kinetics strongly depends both on the Zener-Hollomon parameter and on the amount of strain. The higher content of such impurity elements as silicon and iron gives larger amount of secondary metastable fine particles. This leads to an increase in recrystallization inhibiting force determining recrystallization progress in many respects. Moreover, the number of second phase particles will determine how much the amount of strain affects deformation kinetics. The highest recrystallization rate is observed in pure aluminum, the lowest – in alloy 8006. At low values of the Zener-Hollomon parameter, recrystallization process in this alloy can be fully blocked.This research was funded by the Russian Science Foundation; Project 18-79-10099-П, https://rscf.ru/project/21-79-03041/.

Dynamic impact constitutive relation of 6008-T6 aluminum alloy based on dislocation density and second-phase particle strengthening effects

To investigate the mechanical properties and constitutive relationship of 6008-T6 aluminum alloy under dynamic impact loading, dynamic impact and microscopic experiments were conducted on 6008-T6 aluminum alloy. The results demonstrated that 6008-T6 aluminum alloy exhibits strain hardening effects. As the loading strain rates increased, the grains became more refined, whereas the dislocation density and number of second-phase particles (mainly Mg2Si) increased. Several dislocations interacted with each other, thereby preventing further dislocation movement and improving the material's strength. The precipitation of second-phase particles impeded the motion of dislocations and increased the flow stress of the material. A constitutive model of dynamic impacts was developed based on the evolution of dislocation density and reinforcing effects of second-phase particles. Furthermore, based on the isotropic assumption, the damage evolution equation of 6008-T6 aluminum alloy was obtained by introducing the energy release rate. By combining the dynamic constitutive model of materials under dynamic impact compression conditions, the dynamic constitutive model of materials was obtained under dynamic impact tensile conditions. Moreover, the rationality of the model was confirmed by comparing the model's data with experimental data. In this study, we examined the macro mechanical response, microstructure, and dynamic mechanical behavior of the 6008-T6 aluminum alloy under dynamic impact conditions, which can serve as a theoretical basis and analytical tool for the structural design and safety evaluation of high-speed trains.

A Study on High Strength, High Plasticity, Non-Heat Treated Die-Cast Aluminum Alloy.

The non-heat-treated, die-cast aluminum alloy samples were prepared meticulously via die-casting technology. The crystal structure, microstructure, and phase composition of the samples were comprehensively studied through electron backscatter diffraction (EBSD), metallographic microscopy, spectrometer, and transmission electron microscopy (TEM). The microhardness and tensile properties of the samples were tested. The die-cast samples were found to have desirable properties by studying the structure and performance of the samples. There were no defects, such as pores, cold partitions, or surface cracks, found. The metallographic structure of the samples was mainly α-Al, and various phases were distributed at the grain boundaries. Before heat treating, α-Al grains were mainly equiaxed with a great number of second phase particles at the grain boundaries. After heat treating, the α-Al grains were massive and coarsened, and the second phase grains were refined and uniformly distributed, compared with those before the heat treating. The EBSD results showed that the grain boundary Si particles were solid solution decomposed after heat treatment. The particles became smaller, and their distribution was more uniform. Transmission electron microscopy found that there were nano-scale Al-Mn, Al-Cu, and Cu phases dispersed in the samples. The average microhardness of the samples before heat treating was 114 HV0.1, while, after the heat treating, the microhardness reached 121 HV0.1. The mechanical features of the samples were tremendous, and the obtained die-cast aluminum alloy had non-heat-treatment performance, which was greater than the ordinary die-cast aluminum alloys with a similar composition. The tensile strength of the aluminum alloys reached up to 310 MPa before heat treatment.

Effects of Excessive Zr Content and Ultrasonic Treatment on Microstructure and Mechanical Properties of Al-Zn-Mg-Cu Alloy

The Zr element is one of the important grain refiners for 7xxx series Al-Zn-Mg-Cu alloys, but the effect of Zr content more than 0.15 wt.% needs to be deeply investigated under the action of ultrasonic vibration. In this study, the effects of Zr contents (0.1 to 0.25 wt.%) on microstructure and mechanical properties of Al-Zn-Mg-Cu alloy were studied. The results showed that Zr element could refine grains, but when the Zr content was greater than 0.15 wt.%, the grain size was not uniform, the number of second phase particles increased, and the segregation of components became more serious. It was found that after ultrasonic treatment, the grain-size inhomogeneity was greatly improved, and the Zr content could be added up to 0.2 wt.%. When the Zr content is equal or lower than 0.2 wt.%, ultrasonic treatment can effectively improve the mechanical properties of materials by refining grains and weakening segregation. However, when the Zr content is up to 0.25 wt.%, the effect is getting worse.

Effect of Zn concentration on microstructure and corrosion resistance of Mg-Zn alloys microalloyed with Ca and Ce

PurposeThe influence of Zn concentration on microstructure and corrosion performance of the Mg–xZn alloys microalloyed with Ca and Ce was investigated through optic microscopy, scanning electron microscopy, hydrogen evolution, dynamic polarization and electrochemical impedance spectroscopy experiments.Design/methodology/approachIn this paper, Mg–xZn alloys (x = 0.5∼2.0 Wt.%) microalloyed with Ca and Ce (0.2 Wt.% each) were prepared.FindingsAs the increase of Zn concentration, the number of second phase particles (Mg-Zn-Ca, Mg-Zn-Ce and Mg-Ce phases) increased, and when the Zn concentration increased to 2.0 Wt.%, the new second phase Mg-Zn phase was precipitated.Originality/valueThe influence of Zn concentration on corrosion mechanism of Mg-xZn alloys microalloyed with Ca and Ce was revealed. Increasing of the Zn concentration resulted in the intensification of galvanic corrosion. When Zn concentration was 0.5 Wt.%, the alloy showed the lowest corrosion rate (0.61 mm y-1), which was about 1/2 of that of Mg-2.0Zn-0.2Ca-0.2Ce alloy.

Effects of Nd Addition on the Microstructure and Mechanical Properties of Extruded Mg-6Gd-2.5Y-0.5Zr Alloy

The microstructure, age-hardening behavior, mechanical properties and texture of extruded Mg-6Gd-2.5Y-0.5Zr alloys with various additions of Nd have been investigated through optical microscopy, x-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron back-scattered diffraction, hardness and tensile tests. The results indicate that the number of second-phase particles in the as-extruded alloys increases (especially with the addition of 1.5 wt.% Nd), and the amount of the strengthening β′ phase in the peak-aged sample initially increases, and then decreases when the content of Nd increases above 1.0 wt.%. The precipitation of second-phase particles in the extrusion process weakens the age strengthening. The peak-aged Mg-6Gd-2.5Y-1Nd-0.5Zr alloy shows a maximum yield strength of 259 MPa and an ultimate tensile strength of 350 MPa, which can be attributed to the finely dispersed strengthening β′ phase. All as-extruded alloys exhibit that (0001) planes are aligned perpendicular to the extrusion direction, and the maximum intensity of the texture increases gradually with Nd addition.

A Study on Precipitation Kinetics of an Al-Cu-Li Alloy

Aluminum-Copper-Lithium alloys are of strategic important [1] in lightweight aerospace structures due to their high specific modulus and specific strength and are under consideration for one of the potential choices for Korea Space Launch Vehicle structure. However, this is one of the most complicated alloys due to the precipitation of a large number of second phase particles. In this study, the precipitation kinetics of an Al-4.3%Cu-1.2%Li alloy was studied by differential scanning calorimetry (DSC) technique since precipitation plays an important role for hardening of this alloy. Several models including Kissinger’s, Starink’s and Chaturvedi’s were used to obtain the activation energy and precipitation kinetics.

Texture and stretch formability of rolled Mg–Zn–RE(Y, Ce, and Gd) alloys at room temperature

To develop a new magnesium alloy with excellent formability at room temperature, the effect of Y, Ce, and Gd addition on texture and stretch formability of Mg–1.5Zn alloys was carried out. The result shows that Y, Ce, and Gd addition in Mg–1.5Zn alloys can effectively weaken and modify the basal plane texture, characterized by TD-split texture in which the position of basal is titled from normal direction (ND) toward transverse direction (TD). When Mg–1.5Zn alloy with Gd addition appears low texture intensity and TD-split texture, where the position of basal poles is tilted by about ±35° from ND toward to TD, the largest Erichsen value of 7.0 and the elongation rate reaches 29.1 % in TD direction. However, Y and Ce addition in Mg–1.5Zn alloys promote a large number of second phase particles, which cancel the contribution of the unique basal texture to stretch formability and ductility.

Mg-Sn-Al-Zn 마그네슘 합금 간접압출재의 미세조직 및 소성이방성

Mg-(9-x)Sn-xAl-1Zn (x=1, 2, 3 and 4 wt.%) alloys were subjected to indirect extrusion, and the microstructure and mechanical properties of the as-extruded Mg-Sn-Al-Zn (TAZ) alloys were investigated. The TAZ 811 alloy exhibited a finer grain structure than the TAZ 541 alloy due to a larger number of Mg2Sn particles, which pinned the grain boundaries and prevented growth of recrystallized grains. The TAZ alloys showed an unusual yield asymmetry behavior. The tension-compression yield asymmetry increased with decreasing average grain size. The TAZ 811 alloy with a small grain size exhibited a larger yield asymmetry than that of the TAZ 541 alloy having a relatively large grain size, which is mainly attributed to the low Al content and large number of second phase particles in the TAZ 811 alloy.

Ａｌ‐Ｍｇ‐Ｓｉ系合金の曲げ加工性に及ぼす第２相粒子の影響

The effect of second phase particles on the bendability of Al–Mg–Si alloy for outer panels in autobodies was investigated by changing solution heat treatment condition and quenching rate. Slow quenching rate made inferior bendability. Because the number of second phase particles on the grain boundaries increased. Crack by bending test was not observed with short solution heat treatment time. However, in the case of long solution heat treatment time, the crack was observed. Depth of the crack increased with solution heat treatment time to maximum value and then decreased. The number of second phase particles decreased and the formation of shear bands by deformation increased with solution heat treatment time. When the formation of shear bands is observed significantly and the number of second phase particles is many, the crack occurs easily along the shear bands and the second phase particles.

A positron study on the microstructural evolution of Al-Li based alloys in the early stages of plastic deformation

The formation of voids by coalescence of microvoids initiated at precipitates has been proposed to explain the fracture mechanisms in alloys containing a large number of second phase particles whereas in binary Al-Li alloys with shearable particles the brittleness could be linked with the grain boundary fracture. Most of the microstructure studies of Al-Li alloys have been performed by deforming to fracture; however, little is known about the processes and mechanisms involved in the early stages of plastic deformation. Butler et al. have studied a quaternary Al-Li alloy and have found that there is a critical effective strain to cause voiding, which is about 0.06 and 0.1% for the aged and for the solution treated material respectively. It is very well established that positrons are very sensitive to vacancy-like defects. With the aim of clarifying the behavior of Al-Li based alloys in the very early stages of deformation, and detecting the eventual formation of microvoids, the authors have studied the response of the positron lifetime parameters to the degrees of deformation in age-hardenable Al-Li based alloys plastically deformed under tensile stress.

Thermal analysis studies of the precipitation and dissolution processes of second phases in the Al-Si and Al-Si-Mg systems

In the alloy systems Al-Si and Al-Si-Mg, where Si and Mg typically are in the range 0.5-1.5 w%, a number of second phase particles have been identified, with different composition and crystal structure. To control the conditions under which these particles precipitate and dissolve is very important for controlling the properties of the alloy, like fracture toughness and hardness. In this paper, particularly the influence of the cooling rate in the DSC instrument, with which alloy samples are cooled from a homogeneous phase at high temperature to subambient temperature, has been investigated. Also the total number of heating-cooling cycles applied to a sample has been used as a parameter to explain the different reactions as identified by DSC. The results show a close correlation between the cooling rate and the precipitation/dissolution processes. It was found that the characteristics after a certain cooling rate were different depending on how many cycles that material previously had been through. This can have some implication on estimating the properties of materials in applications were heat and load vary over time.