Grain Size Of Alloy Research Articles

Synthesis of bulk nanostructured Mg-based alloy via spark plasma sintering through in situ crystallization of an amorphous precursor

We present the synthesis of a bulk nanostructured Mg-based alloy that has a grain size less than 300 nm. A nanostructured Mg-Zn-Cu-Nd alloy with an exceptionally high hardness can be obtained through simultaneous consolidation and in situ crystallization of the amorphous Mg84Zn7Cu3Nd6 alloy precursor using the spark plasma sintering process. We evaluate the relationship between the microstructure and preparation conditions on the grain size of nanostructured Mg-based alloys during the sintering process. The hardness of the bulk sample produced from the sintered amorphous Mg-Zn-Cu-Nd precursor at 260 °C is maximized via the nanocrystallization of intermetallic compounds using the sintering process. The populated crystallization and confined growth of phases contribute to the refinement of gains in nanostructured Mg-based alloys.

Multi-scale iron-rich phases induce fine microstructures in Al-Zn-Mg-Cu-Fe alloys

ABSTRACT Multi-scale Al7Cu2Fe and AlFeCu phases are formed in Al-Zn-Mg-Cu-Fe alloys after thermomechanical processing. These multi-scale particles significantly affect the size, morphology, and orientation of recrystallised grains and their corresponding mechanical properties. With increasing concentrations of iron-rich phase particles, the grain size in alloys is significantly reduced from 29.3 μm (0.0Fe wt.%) to 19.9 μm (0.2Fe wt.%) and 17.5 μm (0.4Fe wt.%). The volume fractions of copper, CubeND, and Q all decrease, and the R, Brass, and P textures form with high volume fractions in the #2 alloy. Both the yield and ultimate tensile strengths of the alloys decrease with an increasing iron-rich phase concentration. The highest r value (0.698) is obtained in the #2 alloy due to the improved microstructure and texture distributions from multi-scale iron-rich phases. Finally, the mechanisms of the iron-rich phase evolution, recrystallisation, and high formability in the alloys are introduced.

Microstructure, Micro-Mechanical and Tribocorrosion Behavior of Oxygen Hardened Ti-13Nb-13Zr Alloy.

In the present work, an oxygen hardening of near-β phase Ti–13Nb–13Zr alloy in plasma glow discharge at 700–1000 °C was studied. The influence of the surface treatment on the alloy microstructure, tribological and micromechanical properties, and corrosion resistance is presented. A strong influence of the treatment on the hardened zone thickness, refinement of the α’ laths and grain size of the bulk alloy were found. The outer hardened zone contained mainly an oxygen-rich Ti α’ (O) solid solution. The microhardness and elastic modulus of the hardened zone decreased with increasing hardening temperature. The hardened zone thickness, size of the α’ laths, and grain size of the bulk alloy increased with increasing treatment temperature. The wear resistance of the alloy oxygen-hardened at 1000 °C was about two hundred times, and at 700 °C, even five hundred times greater than that of the base alloy. Oxygen hardening also slightly improved the corrosion resistance. Tribocorrosion tests revealed that the alloy hardened at 700 °C was wear-resistant in a corrosive environment, and when the friction process was completed, the passive film was quickly restored. The results show that glow discharge plasma oxidation is a simple and effective method to enhance the micromechanical and tribological performance of the Ti–13Nb–13Zr alloy.

Effects of Y and Addition of Refiners on Hot Tearing Susceptibility of MgZn-Based Alloy

On the basis of studying the effect of rare earth elements on hot tearing susceptibility (HTS) of Mg–Zn alloys, further exploring effective ways to reduce HTS of Mg–Zn–Y alloys are very important for the development and application of magnesium alloys. In this paper, the effects of 2 at% Y on HTS of MgZn1 alloy and several grain refiners on HTS of MgZn1Y2 alloy were studied. The modified Clyne–Davies model is used to predict the HTS of the investigated alloys, which are found in the descending order: MgZn1 > MgZn1Y2 > MgZn1Y2–0.5 wt% Na2CO3 > MgZn1Y2–0.5 wt% Ti > MgZn1Y2–0.5 wt% Zr. By means of XRD, SEM, TEM and EBSD, the evolution of the microstructure during solidification is revealed. The results show that the addition of 2 at% Y can not refine α-Mg grains, but it can change the precipitation type of the second phase. When the precipitation type of the second phase changes from Mg7Zn3 to Mg12ZnY (LPSO phase) and Mg3Zn3Y2 (W-phase), the solidification end temperature of the alloy increases by more than 100 °C, and the coherent lattice of LPSO and α-Mg has a better bridging effect on the grain boundary, which reduces the HTS by 28.4%. Moreover, the addition of 0.5 wt% Na2CO3, 0.5 wt% Ti or 0.5 wt% Zr is an effective method for α-Mg grain refinement, equiaxation and dendrite coherent delay of MgZn1Y2 alloy. In particular, the addition of 0.5 wt% Zr can reduce the α-Mg grain size of MgZn1Y2 alloy by 89.1% and increase the solid fraction by 45% when dendrites are coherent, which results in a 77.1% reduction in HTS.

Dynamic Impact Response of Ultrafine Grained AA5052 Aluminum Alloy Processed Via Multiaxial Forging at Cryogenic Temperature

In this study, high strain rate mechanical test was conducted on ultrafine-grained AA5052 aluminum alloy using the Split-Hopkinson Pressure Bar experiment. The AA5052 aluminum alloy was processed via multiaxial forging under cryogenic condition at two different cycles to achieve grain refinement and ultimately, increase in strength of the material. The average strain rates that the specimens were subjected to during the Split-Hopkinson Pressure Bar experiment ranges from 1000 s-1 to 5000 s-1 at an increment of 1000 s-1. The EBSD map shows that the average grain size of the AA5052 aluminum alloys for the samples processed at 4-cycles is approximately ~900 nm while the samples processed at 6-cycles have a lower average grain size of approximately ~700 nm due to being subjected to more plastic deformation during the processing. The high strain rate deformation process of both specimens was dominated by thermal softening with minima strain hardening effect. During the deformation, the maximum flow stress experienced by samples that was processed at 4-cycles is 410 MPa at 5000 s-1 strain rate while samples processed at 6-cycles has 494 MPa at 3000 s-1. Strain hardenability is not dominant in the deformation mechanism but relative to AA5052 CF (4-cycles), AA5052 CF (6-cycles) has a better strain hardening exponent as the strain rate increases. Both specimens have the highest strain hardening exponent at 1000 s-1 which is 0.1544 and 0.134 for AA5052 CF (4-cycles) and AA5052 CF (6-cycles), respectively. Our results show that AA5052 CF (6-cycles) possesses better mechanical properties under high strain rate in comparison with AA5052 CF (6-cycles).

Effect of surface modification on the microstructure and sintering characteristics of tungsten nanopowders prepared by a wet chemical method

ABSTRACT In order to prepare high-performance tungsten alloys, surface modification of tungsten nanopowders prepared by a wet chemical method was carried out by acid pickling at room temperature. The low-temperature sintering characteristics of tungsten nanpowders before and after pickling was compared and analysed. The surface modification was carried out by pickling with a solution of hydrofluoric acid, concentrated nitric acid and ammonium fluoride at room temperature. After this surface treatment, uniformly distributed step-shaped defects formed on the surface of the tungsten nanopowders. After low-temperature sintering, the grain size of the tungsten alloy corresponding to the surface-modified powder precursor was reduced by 20% compared to the alloy using untreated powder as precursor. In addition, the step-shaped defects also increase the sintering activity of the pickled tungsten powder and promote its sintering densification, making the final density of pure tungsten sintered at 1600°C as high as 96.7%, and its hardness greatly increased to 521 HV0.2. The results show that room-temperature pickling and subsequent low-temperature sintering is a promising method for preparing high-performance nanotungsten alloys.

Effect of La2O3 content on the densification, microstructure and mechanical property of W-La2O3 alloy via pressureless sintering

In the present work, the influences of La2O3 content (0–5.0 wt%) on the densification and grain growth of tungsten (W) nanopowders during pressureless sintering were systematically investigated. The densification inhibitory effect was enhanced with the increase of the amount of La2O3 addition, resulting in that the densification rate decreases from pure W to W/5.0wt%La2O3 composite powder. However, the grain size of W first decreases from 0 wt% to 2.0wt%La2O3 addition due to the increase of number density of La2O3 particles, and then increases from 2.0 wt% to 5.0wt%La2O3 addition because of the significant increase of the particle size and the decrease of the number density. On the premise of achieving near full density, the grain size of all W-La2O3 alloys sintered by pressureless sintering is very small, only 0.47–1.90 μm. The W-2.0wt%La2O3 alloy sintered at 1650 °C with the grain size of 0.47 μm possesses the highest Vickers microhardness of 739.3 HV0.2.

The role of Gd on the microstructural evolution and mechanical properties of Mg-3Nd-0.2Zn-0.5Zr alloy

This work was undertaken to investigate the specific role of element Gd on the microstructural evolution and mechanical properties of Mg-3Nd-0.2Zn-0.5Zr alloy. It is noticeable that, as the Gd content increases, the average grain size of as-cast alloys is continuously reduced, accompanied by the main secondary phases changing from Mg12Nd to Mg3Gd. Tensile tests reveal that addition of Gd (1.5–4.5 wt%) could lead to substantial enhancements of alloy strength (25–70 MPa) and an excellent combination of strength and ductility is obtained in the alloy with 4.5 wt% Gd addition (YS = 200 MPa, UTS = 343 MPa, EL = 5.4%). Microstructure characterization indicates that the improved solid-solution strengthening effect originated from increasing Gd additions plays a key role in the significant strength improvements obtained in as-quenched alloys. HAADF-STEM observations suggest that Gd is highly enriched in the dominantly disc-like prismatic β″ phases, leading to the strongly enhanced precipitation kinetics and greatly augmented volume fraction of β″ phase. A quantitative microstructural comparison of peak-aged specimens indicates that the significant strength enhancements should be primarily derived from the denser dispersion of β″ phases with higher aspect radio arising from Gd addition.

The Effect of Milling Time and Speed on Solid Solubility, Grain Size, and Hardness of Al-V Alloys

The effect of milling time and speed on solid solubility of V in Al and grain refinement was studied. High-energy ball milling was used to produce Al-xV (x = 2, 5, and 10 at.%) alloys at milling speeds of 280 and 350 RPM. The ball-milling time was varied from 10 to 100 hours. The ball-milled alloys were consolidated under uniaxial pressure of 3GPa at room temperature. The solid solubility of V and grain size after ball milling of Al-xV alloys were estimated using the x-ray diffraction (XRD) analysis. High-energy ball milling imparted the nanocrystalline structure and formation of Al-V solid solution. Grain refinement and solid solubility of V in Al were dependent on the milling speed, milling time, and V content in the alloy.

Corrosion Behavior, Microstructure and Mechanical Properties of Novel Mg-Zn-Ca-Er Alloy for Bio-Medical Applications

In this study, the effect of calcium (Ca) and erbium (Er) on the microstructure, mechanical properties, and corrosion behavior of magnesium-zinc alloys is reported. The alloys were prepared using disintegrated melt deposition (DMD) technique using the alloying additions as Zn, Ca, and Mg-Er master alloys and followed by hot extrusion. Results show that alloying addition of Er has significantly reduced the grain sizes of Mg-Zn alloys and also when compared to pure magnesium base material. It also has substantially enhanced both the tensile and the compressive properties by favoring the formation of MgZn2 type secondary phases that are uniformly distributed during hot-extrusion. The quaternary Mg-Zn-Ca-Er alloy exhibited the highest strength due to lower grain size and particle strengthening due to the influence of the rare earth addition Er. The observed elongation was a result of extensive twinning observed in the alloys. Also, the degradation rates have been substantially reduced as a result of alloying additions and it is attributed to the barrier effect caused by the secondary phases.

Grain refinement and improvement of mechanical properties of AZ31 magnesium alloy inoculated by in-situ oxidation process

Grain refinement is an important technique to improve the mechanical properties of metal materials. In this study, a novel technique (in-situ oxidation process) was proposed. It successfully refined grain and improved the mechanical properties of AZ31 alloy. The effect of different melt treatment process on AZ31 alloy was comparatively studied. For the in-situ oxidation process, effects of flow of O2/Ar mixed gas and the inoculating temperature on grain size were investigated. The results showed that in-situ oxidation process caused an available grain refinement of AZ31 alloy, whereas the only oxidation or the only stirring processes was invalid for grain refinement. After being treated by in-situ oxidation process with an O2/Ar mixed gas flow of 10/100 ml/min, average grain size of AZ31 alloy decreased from 1146 to 554 μm. There existed an effective grain refinement only when O2 gas flow ranges from 5 to 10 ml/min. Oxides (MgO and MgAl2O4) were found in the in-situ oxidation process refined AZ31 alloy. E2EM calculation results indicated that MgO and MgAl2O4 possess a high nucleating potency for α-Mg grain. Measured cooling curves showed that the initial nucleation undercooling declined and the nucleation process ended early. Hence, grain refinement of AZ31 alloy by in-situ oxidation process was attributed to the heterogeneous nucleation of α-Mg grain on MgO and MgAl2O4.

Inverse grain-size-dependent strain rate sensitivity of face-centered cubic high-entropy alloy

It is well documented that the strain rate sensitivity (m) increases at refined grain size for face-centered cubic (FCC) metals and alloys. Through a series of nanoindentation testing, however, we experimentally demonstrated a striking departure from conventional FCC metals that CoCrFeMnNi high entropy alloy (HEA) with FCC lattice structure exhibits monotonously decreased m as grain size reduced from ∼30.3 μm to 7.2 nm. Moreover, the apparent activation volume v*, which generally shows an opposite trend of m, exhibited the identical decreasing trend with reduced grain size as that of m. Such an unusual trend of m and its correlation with v* in the FCC HEA alloys can be understood by a distinct deformation-mechanism-transitions and unique dislocation morphology evolution that differs from conventional FCC metals.

On the statistical correlation between twin deformation and grain size of magnesium alloy under combined tension-torsion cyclic deformation

To study the relationship between the twinning deformation and grain size of a magnesium alloy under combined tension-torsion cyclic (CTTC) loading, CTTC loading experiments with different paths and statistical analysis of the microstructure (grains and twins) were carried out. The test results show that the axial and tangential stress-strain cyclic curves present different symmetrical or asymmetrical characteristics due to the activation of the twinning-detwinning deformation mechanism. The statistical analysis of the microstructure shows that the grain size distribution of the magnesium alloy and the twin thickness distribution in all the grains conform to the Gaussian probability distribution. Furthermore it is found that the statistical correlation between twinning thickness and grain size is not obvious, but the number of twin nuclei is stable and positively correlated with the grain area, and with an increase in the amplitude, additional twin nuclei are produced in the same area of the grain. The research results can provide experimental data for effectively describing the twin deformation mechanism.

A novel continuous squeeze casting-extrusion process for grain refinement and property improvement in AZ31 alloy

Abstract A novel continuous squeeze casting-extrusion (CSCE) process was proposed to prepare high strength and toughness AZ31 alloy. The average grain size of AZ31 alloy after CSCE was reduced to 2.43 μm. An excellent combination of the ultimate tensile strength of 321 MPa and the elongation of 14.7% was achieved.

Effects of Mg Content on Electric and Mechanical Properties of Al-Zn-Cu Based Alloys.

Microstructure and properties of Al-2 wt.%Zn-1 wt.%Cu-xMg (x = 0.1, 0.3, 0.5, 0.7 wt.%) alloy extrusion materials were investigated. The lattice constants for the (311) plane increased to 4.046858, 4.048483, 4.050114 and 4.051149 Å with the addition of 0.1, 0.3, 0.5, and 0.7 wt.% of elemental Mg. The average grain size of the as-extruded Al alloys was found to be 328.7, 297.7, 187.0 and 159.3 μm for the alloys with 0.1, 0.3, 0.5, and 0.7 wt.% Mg content, respectively. The changes in the electrical conductivity by the addition of elemental Mg in Al-2 wt.%Zn-1 wt.%Cu alloy was determined, and it was found that for the addition of 0.1, 0.3, 0.5, and 0.7 wt.% Mg, the conductivity decreased to 51.62, 49.74, 48.26 and 46.80 %IACS. The ultimate tensile strength of Al-2 wt.%Zn-1 wt.%Cu-0.7 wt.%Mg alloy extrusion was increased to 203.55 MPa. Thus, this study demonstrated the correlation between the electrical conductivity and strength for the Al-2 wt.%Zn-1 wt.%Cu-xMg alloys.

Effect of annealing temperature and cutting angle of specimens on metallurgical and mechanical properties of Mg-7Li-1Zn alloy via Taguchi approach and response surface analysis

The main aim of this research is to assess the effect of annealing temperature and cutting angle of specimens on the metallurgical and mechanical properties of superlight Mg-Li-Zn alloy thin sheets. To this end, as-rolled LZ71 (Mg-7%Li-1%Zn) alloy was annealed at different temperatures (0, 250, and 350° C) for 3 hours. After that, the test specimens were cut at different angles relative to the rolling direction (0, 45, and 90 °). Next, several experiments were accomplished to study the microhardness, microstructure, grain size, and tensile behavior of the LZ71 alloy. Finally, different Design of Experiment (DOE) techniques were used to determine the individual and interaction effects of annealing temperature and cutting angle of specimens on the material characterization of LZ71 alloy. In this regard, annealing temperature and cutting angle were considered as input parameters in both Taguchi Approach (TA) and Response Surface Analysis (RSA). Also, key parameters of the tensile test including Ultimate Tensile Strength (UTS), Yield Stress (YS), Elastic Modulus (EM), and Strain at BreakPoint (SBP) were considered as outputs. It was concluded that annealing temperature influence on the static behavior of LZ71 alloy is several times greater than the effect of cutting angle (i.e., the effect of annealing temperature on the UTS, YS, EM, and SBP is 92%, 76%, 61%, and 66%, respectively). Moreover, the results of the Response Surface Optimization Algorithm (RSOA) showed that to achieve the best static properties in different directions, the annealing temperature should be selected to be 350°C.

Microstructural and textural evolution of Al-4.5Mg-0.7Mn-0.2Sc alloys during hot rolling

In general, the Al-Mg-Mn-Sc alloys are not strengthened by heat treatment. Rather, hot rolling process renders a great influence on subsequent performance. Herein, the recrystallization annealing is carried out during the hot rolling process of alloy plates, and microstructural and texture evolution is systematically studied. The results reveal that the grain size of alloy significantly decreased from 169.226 µm to 24.4885 µm after recrystallization annealing and hot rolling. Also, the obvious dynamic recrystallization and a large number of dislocation walls are observed in the grains, which are conducive to the continuous hot machining of Al-Mg-Mn-Sc alloys with large deformation. In addition, the texture strength of alloy plate is increased due to recrystallization and grain orientation is significantly altered, where the grain orientation changed from 〈111〉 to 〈101〉 direction.

The influence of gadolinium on Al–Ti–C master alloy and its refining effect on AZ31 magnesium alloy

Abstract Grain refinement has a significant influence on the improvement of mechanical properties of magnesium alloys. In this study, a series of Al–Ti–C-xGd (x = 0, 1, 2, 3) master alloys as grain refiners were prepared by self-propagating high-temperature synthesis. The synthesis mechanism of the Al–Ti–C-xGd master alloy was analyzed. The effects of Al–Ti–C-xGd master alloys on the grain refinement and mechanical properties of AZ31 (Mg-3Al-1Zn-0.4Mn) magnesium alloys were investigated. The results show that the microstructure of the Al–Ti–C-xGd alloy contains α-Al, TiAl3, TiC and the core–shell structure TiAl3/Ti2Al20Gd. The refining effect of the prepared Al–Ti–C–Gd master alloy is obviously better than that of Al–Ti–C master alloy. The grain size of AZ31 magnesium alloy was reduced from 323 μm to 72 μm when adding 1 wt.% Al–Ti–C-2Gd master alloy. In the same condition, the ultimate tensile strength and elongation of as-cast alloy were increased from 130 MPa, 7.9% to 207 MPa, 16.6% respectively.

Nano-yttrium-containing precipitates of T6 heat-treated A356.2 alloy when trace yttrium (Y less than 0.100 wt%) added

To investigate the effect of yttrium (Y) on microstructure refinement and mechanical properties of aluminum alloy A356.2, the different trace contents of Y (0 wt%, 0.025 wt%, 0.050 wt%, 0.075 wt%, or 0.100 wt%) were introduced into the liquid alloy. The alloys were fabricated in a preheated permanent mold, and subsequently treated by a T6 heat treatment. The results of tensile testing indicate that the yield strength (YS), the ultimate tensile strength (UTS) and the elongation (El) of the A356.2 alloy are improved by the Y additions. The YS dependence on grain size for the test alloys follows the Hall–Petch equation, which gives $${\text{YS}} = - 354.1 + {2875}{\text{.2}}d^{ - 1/2}$$ with a correlation of R2 = 0.83. As 0.050 wt% Y is added, the optimum values of the YS, UTS and El are achieved after T6 heat treatment. The secondary phases were identified by X-ray diffraction (XRD) which mainly consisted as Si, Mg2Si and Al3Y. The scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS) analyses reveal the presence of the nano-sized Al3Y particles on the surface of the Si phase. The A356.2 alloy with the Y addition is strengthened by the dendritic refinement, and the presence of the micron- and nano-sized Al3Y precipitates.

Effect of cooling rate on solidification microstructure and mechanical properties of TiB2-containing TiAl alloy

Effects of cooling rate and 0.25 at.% TiB 2 addition on solidification microstructure and mechanical properties of Ti–48Al–2Cr–2Nb alloys fabricated by the investment casting with different thicknesses were studied. The results show that with the cooling rate increasing from 37 to 2×10 2 K/s, the solidification path of the studied alloys is unchanged. The grain size of the matrix alloy is refined from 650 to 300 μm, while the grain size of Ti–48Al– 2Cr–2Nb–TiB 2 is reduced from 550 to 80 μm. The lamellar spacing of matrix alloy is reduced from 360 to 30 nm with increasing the cooling rate from 37 to 2×10 2 K/s, while TiB 2 addition shows little refinement effect on the lamellar spacing. Ti–48Al–2Cr–2Nb–TiB 2 sample under medium cooling rate (69 K/s) exhibits superior microhardness (HV 550) and ultimate tensile strength (570 MPa) among the studied alloys. The refined grain size, lamellar spacing and fine TiB 2 particles could account for the favorable mechanical properties of the studied TiB 2 -containing alloy. The microstructure evolution was discussed in light of cooling rate, constitutional supercooling and borides addition.