Two-stage dynamic recrystallization and texture evolution in Al-7Mg alloy during hot torsion

Hot torsion tests were performed on the Al-7Mg alloy at the temperature ranging from 300 to 500℃ and strain rates between 0.05 and 5 s^(-1) to explore the progressive dynamic recrystallization(DRX)and texture behaviors.The DRX behavior of the alloy manifested two distinct stages:Stage 1 at strain of≤2 and Stage 2 at strains of≥2.In Stage 1,there was a slight increase in the DRXed grain fraction(X_(DRX))with predominance of discontinuous DRX(DDRX),followed by a modest change in X_(DRX) until the transition to Stage 2.Stage 2 was marked by an accelerated rate of DRX,culminating in a substantial final X_(DRX) of~0.9.Electron backscattered diffraction(EBSD)analysis on a sample in Stage 2 revealed that continuous DRX(CDRX)predominantly occurred within the(121)[001]grains,whereas the(111)[110]grains underwent a geometric DRX(GDRX)evolution without a noticeable sub-grain structure.Furthermore,a modified Avrami’s DRX kinetics model was utilized to predict the microstructural refinement in the Al-7Mg alloy during the DRX evolution.Although this kinetics model did not accurately capture the DDRX behavior in Stage 1,it effectively simulated the DRX rate in Stage 2.The texture index was employed to assess the evolution of the texture isotropy during hot-torsion test,demonstrating significant improvement(>75%)in texture randomness before the commencement of Stage 2.This initial texture evolution is attributed to the rotation of parent grains and the substructure evolution,rather than to an increase in X_(DRX).

Electrochemical Hydrogen Charging on Corrosion Behavior of Ti-6Al-4V Alloy in Artificial Seawater

This study employs advanced electrochemical and surface characterization techniques to investigate the impact of electrochemical hydrogen charging on the corrosion behavior and surface film of the Ti-6Al-4V alloy.The findings revealed the formation ofγ-TiH andδ-TiH_(2) hydrides in the alloy after hydrogen charging.Prolonging hydrogen charging resulted in more significant degradation of the alloy microstructure,leading to deteriorated protectiveness of the surface film.This trend was further confirmed by the electrochemical measurements,which showed that the corrosion resistance of the alloy progressively worsened as the hydrogen charging time was increased.Consequently,this work provides valuable insights into the mechanisms underlying the corrosion of Ti-6Al-4V alloy under hydrogen charging conditions.

Effect of addition of minor amounts of Sb and Gd on hot tearing susceptibility of Mg-5Al-3Ca alloy

The effects of addition of minor amount of(0.5 wt.%) antimony(Sb) or gadolinium(Gd) and combined addition of Sb and Gd(0.5 wt.%,respectively) on the hot tearing susceptibility(HTS) of Mg-5Al-3Ca alloy were investigated experimentally using a “T-shaped” hot tearing measuring system. Various solidification parameters of the alloys were measured and calculated through thermal analysis experiments. The microstructure, grain size, and morphology of the crack zone were characterized by scanning electron microscopy and electron backscatter diffraction, and the crystal phases of the alloys were analyzed by X-ray diffraction and energy-dispersive X-ray spectroscopy. The results showed that the addition of 0.5 wt.% Gd resulted in the increase in the vulnerable temperature range(Tv) and reduced the eutectic structure content that could participate in feeding, thereby improving the HTS of the alloy. However, addition of 0.5 wt.% Sb or combined addition of Gd and Sb(0.5 wt.%, respectively) to the Mg-5Al-3Ca alloy shortened the Tvand improved the skeleton strength of the alloy, thereby reducing HTS. Moreover, significantly refined structure of Mg-5Al-3Ca-0.5Gd-0.5Sb alloy improved the feeding ability of the eutectic structure, thus the alloy exhibited the lowest HTS.

Investigation of the Laser Powder Bed Fusion Process of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Alloy

Laser powder bed fusion(LPBF)is an advanced manufacturing technology;however,inappropriate LPBF process parameters may cause printing defects in materials.In the present work,the LPBF process of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy was investigated by a two-step optimization approach.Subsequently,heat transfer and liquid flow behaviors during LPBF were simulated by a well-tested phenomenological model,and the defect formation mechanisms in the as-fabricated alloy were discussed.The optimized process parameters for LPBF were detected as laser power changed from 195 W to 210 W,with scanning speed of 1250 mm/s.The LPBF process was divided into a laser irradiation stage,a spreading flow stage,and a solidification stage.The morphologies and defects of deposited tracks were affected by liquid flow behavior caused by rapid cooling rates.The findings of this research can provide valuable support for printing defect-free metal components.

Effect of Ti on microstructure and properties of electromagnetic stirred Al-18wt.%Mg_(2)Si alloy

By adding different amounts of Ti into the electromagnetic stirred Al-18wt.%Mg_(2)Si alloy,the effect of Ti element on the microstructure and mechanical properties of the alloy was studied.The experimental results show that the microstructure is refined after modification with Ti,which is related to the heterogeneous nucleation of TiAl_(3) particles on theα-Al matrix.With the increase of Ti content and holding time after stirring,the primary Mg_(2)Si phase is refined firstly and then coarsened,and correspondingly,the mechanical properties of the alloy show a trend of increasing at first and then decreasing.When the addition of Ti is 0.5wt.%and the holding time is about 20 min,the refinement effect of primary Mg_(2)Si phase is the most significant and the mechanical properties of the alloy are optimal.

Artificial Neural Network and Fuzzy Logic Based Techniques for Numerical Modeling and Prediction of Aluminum-5%Magnesium Alloy Doped with REM Neodymium

In this study, the mechanical properties of aluminum-5%magnesium doped with rare earth metal neodymium were evaluated. Fuzzy logic (FL) and artificial neural network (ANN) were used to model the mechanical properties of aluminum-5%magnesium (0-0.9 wt%) neodymium. The single input (SI) to the fuzzy logic and artificial neural network models was the percentage weight of neodymium, while the multiple outputs (MO) were average grain size, ultimate tensile strength, yield strength elongation and hardness. The fuzzy logic-based model showed more accurate prediction than the artificial neutral network-based model in terms of the correlation coefficient values (R).

Modification of Mg_2Si in Mg-Si alloys with neodymium

The modification effect of neodymium （Nd） on Mg2Si in the hypereutectic Mg-3%Si （mass fraction） alloy was investigated by optical microcopy, scanning electron microscopy and X-ray diffraction. The results indicate that the morphology of the primary Mg2Si transforms from coarse dendrite into fine polygon with increasing Nd content. The average size of the primary Mg2Si significantly decreases to about 10 ~ma with increasing Nd content up to 1.0%, and then becomes coarser again. The modification and refinement of the primary Mg2Si are mainly attributed to the poisoning effect. The NdMg2 phase in the primary Mg2Si transforms into NdSi and NdSi2 compounds as the Nd content exceeds 3.0%. Therefore, it is reasonable to conclude that the proper Nd （1.0%） addition can effectively modify and refine the primary Mg2Si.

Grain refining mechanism of Al-3B master alloy on hypoeutectic Al-Si alloys

Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ＇Al-AlB2＇ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α（Al） phase.

Effect of wet shot peening on Ti-6Al-4V alloy treated by ceramic beads

Ti-6Al-4V alloy was processed by wet shot peening with ceramic beads. The effects of the shot peened intensity on the microstructure, surface morphology, and residual stress were investigated. A tensile-tensile fatigue test was performed and the fracture mechanism was proposed. The results demonstrate that the surface roughness after wet shot peening is obviously lower than that after dry shot peening. With the increase of the shot peened intensity, the depth of the residual stress layer increases to 250 ktrn, and the maximum stress in this layer increases to -895 MPa. The fatigue strength also increases by 12.4% because of the wet shot peening treatment. The dislocation density of the surface layer is significantly enhanced after the wet shot peening with ceramic beads. The microstructure of the surface layer is obviously refined into ultra-fine grains.

Effects of Mn and Sn on microstructure of Al-7Si-Mg alloy modified by Sr and Al-5Ti-B

The effects of Mn and Sn on the microstructure of Al?7Si?Mg alloy modified by Sr and Al?5Ti?B were studied. The results show that the columnar dendrites structure is observed with high content of Sr, indicating a poisoning effect of the Al?5Ti?B grain refinement. In addition, Sr intermetallic compounds distribute on the TiB2 particles, which agglomerate inside the eutectic Si. The mechanism responsible for such poisoning was discussed. The addition of Mn changes the morphology of iron intermetallic compounds fromβ-Al5FeSi toα-Al(Mn,Fe)Si. Increasing the amount of Mn changes the morphology ofα-Al(Mn,Fe)Si from branched shape to rod-like shape with branched distribution, and finally convertsα-Al(Mn,Fe)Si to Chinese script shape. The microstructure observed by transmission electron microscopy (TEM) shows that Mg is more likely to interact with Sn in contrast with Si under the effect of Sn. Mg2Sn compound preferentially precipitates between the Si/Si interfaces and Al/Si interfaces.

Hot deformation behavior of Al-9.0Mg-0.5Mn-0.1Ti alloy based on processing maps

Hot deformation behavior of extrusion preform of the spray-formed Al-9.0Mg-0.5Mn-0.1Ti alloy was studied using hot compression tests over deformation temperature range of 300-450 ℃ and strain rate range of 0.01-10 s-1. On the basis of experiments and dynamic material model, 2D processing maps and 3D power dissipation maps were developed for identification of exact instability regions and optimization of hot processing parameters. The experimental results indicated that the efficiency factor of energy dissipate （η） lowered to the minimum value when the deformation conditions located at the strain of 0.4, temperature of 300 ° C and strain rate of 1 s-1. The softening mechanism was dynamic recovery, the grain shape was mainly flat, and the portion of high angle grain boundary （〉15°） was 34%. While increasing the deformation temperature to 400 ° C and decreasing the strain rate to 0.1 s-1, a maximum value of η was obtained. It can be found that the main softening mechanism was dynamic recrystallization, the structures were completely recrystallized, and the portion of high angle grain boundary accounted for 86.5%. According to 2D processing maps and 3D power dissipation maps, the optimum processing conditions for the extrusion preform of the spray-formed Al？9.0Mg？0.5Mn？0.1Ti alloy were in the deformation temperature range of 340-450 ° C and the strain rate range of 0.01-0.1 s-1 with the power dissipation efficiency range of 38%？43%.

Tribocorrosion behaviors of Ti-6Al-4V and Monel K500 alloys sliding against 316 stainless steel in artificial seawater

The tribocorrosion behaviors of Ti-6Al-4V and Monel K500 alloys sliding against 316 stainless steel were investigated using a ring-on-block test rig in both artificial seawater and distilled water. It is found that friction coefficients are in general larger in distilled water compared with seawater. The wear losses of Ti-6Al-4V and Monel K500 alloys are larger in seawater compared with distilled water. The mechanical action can destroy the passive film and increase the corrosion rate. The synergism effect between corrosion and wear occurs. The synergism action between corrosion and wear is related to the corrosion rate and with the increase of corrosion rate, the synergism becomes more important. 316 stainless steel suffers severe wear sliding against Monel K500 alloy compared with sliding against Ti-6Al-4V alloy in both distilled water and seawater.

Mechanical properties of strengthened surface layer in Ti-6Al-4V alloy induced by wet peening treatment

A modified surface layer was formed on Ti-6Al-4V alloy by wet peening treatment. The variations of the residual stress,nano-hardness and microstructure of the modified layer with depth from surface were studied using X-ray diffraction analysis,nano-indentation analysis, scanning electron microscopy and transmission electron microscopy observations. The results show thatboth the compressive residual stress and hardness decrease with increasing depth, and the termination depths are 160 and 80 μm,respectively. The microstructure observation indicates that within 80 μm, the compressive residual stress and the hardness areenhanced by the co-action of the grain refinement strengthening and dislocation strengthening. Within 80–160 μm, the compressiveresidual stress mainly derives from the dislocation strengthening. The strengthened layer in Ti-6Al-4V alloy after wet peeningtreatment was quantitatively analyzed by a revised equation with respect to a relation between hardness and yield strength.

Effects of neodymium addition on microstructure and mechanical properties of near-eutectic Al-12Si alloys

The microstructure and mechanical properties of near-eutectic Al-12 Si alloys modified with 0-0.4% Nd（mass fraction） were investigated. The results indicate that a submicro- or nano-sized Al2 Nd phase is observed in the modified alloy with 0.3% Nd. The morphology of the α（Al） phase is significantly refined in the Nd-modified alloys. The primary Si morphology simultaneously changes into a fine, particle-like morphology, and the morphology of eutectic Si becomes fine-fibrous instead of coarse-acicular. Relatively few growth twins are observed on the surface of the Si plate in the Al-12Si-0.3Nd alloy at the optimal modification level. The mechanical property test results confirm that the mechanical properties of the as-cast Al-12 Si alloys are enhanced after the Nd addition, with optimal ultimate tensile strength（UTS） of 252 MPa and elongation（EL） of 13% at an Nd content of 0.3%. The improved mechanical properties are attributed to the refined morphology of Si phase and the formation of the Al2 Nd phase.

Process parameters optimization of Ti-6Al-4V alloy sheet during hot stretch-creep forming

Hot stretch-creep forming （SCF） is a novel technique to produce hard-to-form thin-walled metal components. Comprehensively considering the analysis results of the springback angle, yield strength and microstructure, four hot SCF process parameters including temperature, stretch velocity, post stretch percentage and dwelling time of a Ti-6Al-4V alloy sheet were optimized using an orthogonal experiment. The results reveal that temperature is the most important factor on springback angle. The yield strength of the deformed material in 0° direction increases, while those in directions of 45° and 90° fluctuate around the original value. After hot SCF, the shape of some a phases changes from short thin grains to long slender ones, and the microhardness changes very little. The optimized parameters with temperature of 700 ℃, stretch velocity of 5 mm/min, post stretch percentage of 2% and dwelling time of 8 min are achieved finally.

Influence of hydrogen content on room temperature compressive properties of Ti-6Al-4V alloy at high strain rate

Electromagnetic forming tests were done at room temperature to reveal the influence of hydrogen content on the compressive properties of Ti-6Al-4V alloy at high strain rate. Microstructure was observed to reveal the mechanism of hydrogen-enhanced compressive properties. The experimental results indicate that hydrogen has favorable effects on the compressive properties of Ti-6Al-4V alloy at high strain rate. Compression of Ti-6Al-4V alloy first increases up to a maximum and then decreases with the increase of hydrogen content at the same discharge energy under EMF tests. The compression increases by 47.0% when 0.2% (mass fraction) hydrogen is introduced into Ti-6Al-4V alloy. The optimal hydrogen content for cold formation of Ti–6Al–4V alloy under EMF was determined. The reasons for the hydrogen-induced compressive properties were discussed.

In situ study on columnar-equiaxed transition and anaxial columnar dendrite growth of Al-15%Cu alloy by synchrotron radiography

Directional solidification of Al-15% （mass fraction） Cu alloy was investigated by in situ and real time radiography which was performed by Shanghai synchrotron radiation facility （SSRF）. The imaging results reveal that columnar to equiaxed transition （CET） is provoked by external thermal disturbance. The detaching and floating of fragments of dendrite arms are the prelude of the transition when the solute boundary layer in front of the solid-liquid interface is thin. And the dendrite triangular tip is the fracture sensitive zone. When the conditions are suitable, new dendrites can sprout and grow up. This kind of dendrite has no obvious stem and is named anaxial columnar dendrites.

Effects of stabilizing heat treatment on microstructures and creep behavior of Zn-10Al-2Cu-0.02Ti alloy

The microstructures of as-extruded and stabilizing heat-treated Zn-10Al-2Cu-0.02Ti alloys were observed by scanning electron microscopy,transmission electron microscopy,electron probe microanalysis and X-ray diffraction analysis techniques.The change in structure after heat treatment and its effects on room temperature creep behavior were investigated by creep experiments at constant stress and slow strain rate tensile tests.The results show that after stabilizing heat treatment（（350℃,30 min,water-cooling）＋（100℃,12 h,air-cooling））,the amount of α＋η lamellar structure decreases,while the amount of cellular and granular structure increases.The heat-treated Zn-10Al-2Cu-0.02Ti alloy exhibits better creep resistance than the as-extruded alloy,and the rate of steady state creep decreases by 96.9% after stabilizing heat treatment.

Dynamic fracture of Ti-6Al-4V alloy in Taylor impact test

The dynamic fracture behaviors of Ti-6Al-4V alloy at high strain rate loading were investigated systemically through Taylor impact test, over the range of impact velocities from 145 m/s to 306 m/s. The critical impact velocity of fracture ranges from 217 m/s to 236 m/s. Smooth surfaces and ductile dimple areas were observed on the fracture surfaces. As the impact velocity reached 260 m/s, the serious melting regions were also observed on the fracture surfaces. Self-organization of cracks emerges when the impact velocity reaches 260 m/s, while some special cracks whose ＂tips＂ are not sharp but arc and smooth, and without any evidence of deformation or adiabatic shear band were also observed on the impact end surfaces. Examination of the sections of these special cracks reveals that the cracks expand along the two maximum shear stress directions respectively, and finally intersect as a tridimensional ＂stagger ridge＂ structure.

Effect of grain size of primary α phase on bonding interface characteristic and mechanical property of press bonded Ti-6Al-4V alloy

The effect of grain size of primary α phase on the bonding interface characteristic and shear strength of bond was investigated in the press bonding of Ti-6Al-4V alloy. The quantitative results show that the average size of voids increases from 0.8 to 2.6 μm and the bonding ratio decreases from 90.9% to 77.8% with an increase in grain size of primary α phase from 8.2 to 16.4 μm. The shape of voids changes from the tiny round to the irregular strip. The highest shear strength of bond can be obtained in the Ti-6Al-4V alloy with a grain size of 8.2 μm. This is contributed to the higher ability of plastic flow and more short-paths for diffusion in the alloy with smaller grain size of primary α phase, which promote the void closure process and the formation of α/β grains across bonding interface.