Dynamic Recrystallization Zone Research Articles

Long‐Term Corrosion Behavior Study of Aluminum‐Alloy/Stainless‐Steel Inertia Friction–Welded Tank Storing N2O4

In this work, the materials from different positions of 2219 aluminum‐alloy/304 stainless‐steel inertia friction–welded tank with long‐term storage of N2O4 are studied. The results show that the corrosion product layer composed of Fe3O4 and FeCr2O4 is covered on the surface of stainless steel. The corrosion product layer on the surface of stainless steel can effectively improve the protection effect. Severe corrosion occurred in both the sidewall and bottom aluminum alloy, with intergranular corrosion depths of about 30–50 μm observed in the cross section, accompanied by typical exfoliation corrosion. A Fe–Al‐dominated intermetallic compound layer is formed at the weld. A dynamic recrystallization zone and thermomechanical‐affected zone are included on the aluminum‐alloy side with intergranular corrosion depths of 4.3 and 13.3 μm, respectively. The granular Al matrix can be seen on the peeling surface of the aluminum alloy. Combining scanning Kelvin probe and potentiodynamic polarization curve results, the high potential of the stainless steel can further promote the corrosion of the aluminum alloy.

Hot deformation and microstructural evolution of ultrasonically fabricated as-cast Al-7.3Zn-2.2Mg-2Cu alloy

Al-7.3Zn-2.2 Mg-2Cu alloy is known for its high strength, achieved because of higher alloying concentration. However, the higher alloying concentration presents challenges during the hot deformation process. Nevertheless, hot deformation proves to be an effective method for optimizing the microstructural and mechanical properties of the material. The research presented in the study focuses on investigating the hot working response of an ultrasonically fabricated age-hardening as-cast Al-7.3Zn-2.2 Mg-2Cu alloy. The objective is to observe the attainment of a uniform and dendrite-free microstructure after a single-step hot compression. The flow stress of the deformed specimens showed a notable increase as the temperature and deformation time decreased. This increase in stress was influenced by various factors, including deformation variables and precipitate size. The accurate prediction of the hot deformation behaviour was achieved by combining the constitutive equations and a workability map. The 3-dimensional workability map revealed a gradually increasing power dissipation efficiency (PDE) from 40% to 50% with increasing strain. At the end of 50% compression, four specific optimum working regions (PDE > 40%) were identified. Through detailed microstructural analysis, the best region for hot forging of ultrasonically mixed as-cast alloy for chemical homogeneity and upgraded property is obtained in the range of (350–450 °C) & (0.1–0.001 s−1). The highest extent of recrystallization (73%) was exhibited after deformation at 450 °C-0.001 s−1. The mechanism of dynamic softening during deformation is observed due to DRV, CDRX, and PSN. The microstructural response in 0.1–0.001 s−1 and 350–450 °C indicated dynamic recrystallization, whereas strained and non-working zone was observed at low deformation temperatures (≤350 °C).

Flow behavior during solder/Cu column friction plunge micro-welding

PurposeThe author proposed a friction plunge micro-welding (FPMW) method and applied it to column grid array packaging to realize the connection of copper columns without precision molds assisted positioning. The purpose of this paper is to study the flow behavior of the solder undergoing frictional thermo-mechanical action during the FPMW and to determine the source of the solders in the micro-zones with different microstructure characteristics near the solder/Cu column friction interface.Design/methodology/approachThree kinds of Sn58Bi/SAC305 and SAC305/Pb90Sn composite solder samples were designed to study the flow behavior of the solder during FPMW using Bi and Pb as tracer elements.FindingsThe results show that most of the solders in the position occupied by the copper column was softened and plasticized during the welding process and was extruded to side of the copper column, flowing axially, circumferentially and radially along a trajectory similar to a conical spiral line. Under the drive of the tangential friction force and the radial hold-tight force, the extruded out visco-plastic solders fully mixed with the visco-plastic solders on the sides of the copper column, and bonded with the solders that deformed plastically on the periphery, so that a stir zone and a dynamic recrystallization zone finally evolved. The outside plastically deformed solders evolved into a thermo-mechanical affected zone.Originality/valueThe flow behavior of the solder during the FPMW was determined, as well as the source of the solders in micro-zones with different microstructure characteristics.

Effect of Rotation Speed on Microstructure and Mechanical Properties of Continuous Drive Friction Welded Dissimilar Joints of 6061-T6 Al and Copper

The continuous drive friction welding of 6061-T6 Al and copper was investigated herein. The results show that with an increase in rotation speed, the width of the welded zone was gradually increased with the generation of higher temperatures, and the grain size in the dynamic recrystallization zone on the Al side first decreased and then increased due to the combined effect of heat and force. The microhardness on the bonding surface was significantly greater than that of the base materials due to the presence of intermetallic compounds, and there was a softening zone on both sides of the bonding surface, which was progressively more significant with an increase in the rotation speed. The ultimate tensile strength (UTS) of the welded joints first increased and then decreased with an increase in rotation speed. When the rotation speed was 1000 rpm, the UTS was at its peak value of 212 MPa, which reached 73.1% of the strength of the 6061-T6 Al base material.

Effect of Cr elimination on flow behavior and processing map of newly developed ECO-7175 aluminum alloy during hot compression

ECO-Al alloys are introduced as a game-changer for the aluminum industry and it is of utmost importance to determine the role of alloying elements in their processing characteristics. In this study, the effects of Cr on the hot deformation behavior of newly-developed ECO-7175 alloy were investigated. ECO-7175 samples with and without Cr were hot-compressed using a Gleeble simulator (temperature range of 350−500 °C and strain rates of 0.001−1 s−1). The results were used to study the constitutive equations, the processing maps, and the microstructural evolution of the alloys. In Cr-containing alloy, the analysis of the deformation activation energy reveals that the rate-controlling mechanisms of the deformation change gradually from self-diffusion of Al (or diffusion of Mg in Al) to diffusion of Cr in Al by decreasing the Zener−Hollomon parameter. The analysis of the processing maps of Cr-containing alloy shows that the dynamic recrystallization (DRX) zone is limited to the deformation at high temperatures and low strain rates and expands with increasing applied strain. On the other hand, it is found that the self-diffusion of Al (or Mg in Al) is the only rate-controlling mechanism during hot deformation of Cr-free alloy in all processing conditions and its DRX zone is independent of the plastic strain.

Effect of post-weld heat treatment on inhomogeneity of mechanical properties and corrosion behavior of rotary friction welded 2024 aluminum alloy joint

The effects of different aging treatment conditions on inhomogeneity of mechanical properties and corrosion behavior of rotary friction welded (RFWed) AA2024 joints were studied by artificial and natural aging treatment. The sliced samples at the center, 0.25R, 0.5R and 0.75R positions were taken along the radius of RFWed joint. After artificial aging and long-term natural aging treatment, the tensile strength and corrosion resistance in different positions of joint tended to be homogeneous. Furthermore, the distribution of elements existed in the interior of grain and grain boundary was homogeneous after artificial aging, which reduced the tendency of intercrystalline corrosion. And pitting corrosion occurred at dynamic recrystallization zone (DRZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM). The order of corrosion resistance of each region was inferred from the electrochemical parameters as BM > TMAZ > HAZ > DRZ. With the prolongation of natural aging time, the best corrosion resistance occurred in BM, while the corrosion types of DRZ, TMAZ and HAZ gradually changed from pitting and intergranular corrosion to pitting corrosion mainly.

Relationship between the initial {100} textures and the shear textures developed in sheet surface during hot rolling of non-oriented silicon steel

The texture and microstructure variation through thickness of hot-rolled sheets can inherit to the final recrystallized sheets in silicon steels, thereby affecting final magnetic properties. A systematic study on the evolution of shear textures in hot-rolled sheets is of great importance for controlling and improving the magnetic properties of industrial products. The relationship between the initial {100} textures in cast slabs with columnar grains and the shear textures developed in surface of hot rolled sheets was studied in this work. The formation of the shear textures in the sheet surface was tracked during hot rolling of columnar grained cast slabs with 30% ~ 90% reductions. The results show that the cube orientation {100}<001> usually rotates to the Goss orientation {110}<001> around the <100>//RD axis; the {001}<120> orientation rotates to the Brass type orientation {110}<112> around the <100> axis parallel the rolling plane; and rotated cube orientation {100}<011> rotates to the Copper type orientation {112}<111> around the <110>//TD axis. Goss and Brass oriented regions appear earlier than Copper oriented regions. More than a quarter of the cube and {001}<120> oriented regions are retained in the surface regions of hot-rolled sheets even after 88% rolling reduction. Considering beneficial Goss texture for magnetic properties of final sheets and texture heredity, the hot rolling conditions are controlled at threshold before formation of dynamic recrystallization zone that is more preferred.

Effect of inhomogeneous microstructure evolution on the mechanical properties and corrosion behavior of rotary friction welded AA2024 joints

The intrinsic flaws of radial gradient heat generation and uneven deformation during rotary friction welding process will damage the structural integrity of the resultant joint but almost no attention has been paid before. The relationship between radial inhomogeneous microstructure, mechanical properties and corrosion behavior of rotary friction welded 2024 aluminum alloy joint was thus systematically investigated to reveal the impact. The results showed that the highest and lowest tensile strength appeared in 0.25R and 0.75R positions along radius, respectively. And the texture evolution in 0.25R and 0.75R positions can be summarized as: Copper {112}<111> → S{123}<634> → Brass {011}<211>(strong) → Brass {011}<211> (weak), Copper {112}<111> → S{123}<634> → Rotated Goss {110}<110> → Brass {011}<211> (weak), respectively. The corrosion resistance of rotary friction welded joint is gradually weakened along radius, caused by the different distribution of grain size, second phase particles and residual stress. The heat affected zone (HAZ), thermo-mechanically affected zone (TMAZ) adjacent to HAZ and dynamic recrystallization zone (DRZ) exhibited high corrosion susceptibility and occurred severe exfoliation corrosion. But the TMAZ adjacent to DRZ and base metal acquired the good corrosion resistance due to the dispersive distribution of GPB zones. Furthermore, the qualitative relationship between microhardness and corrosion susceptibility was revealed. The regions with low microhardness exhibited high corrosion susceptibility while the regions with high microhardness (except DRZ) presented good corrosion resistance. • Microstructure and mechanical properties of joints unevenly distributed along radius. • Texture evolution in 0.25R and 0.75R position was systematically investigated. • The corrosion resistance in TMAZ adjacent to DRZ is the highest. • Qualitative relation between microhardness and corrosion susceptibility was revealed.

Friction welding of dissimilar joints copper-stainless steel pipe consist of 0.06 wall thickness to pipe diameter ratio

This paper examines dissimilar friction welding between electrolytic tough pitch copper (ETP-Cu) and stainless steel (SS) of grade 304 L for pipe joint configuration, having 0.06 wall thickness to pipe diameter ratio. The welding is performed using the continuous drive friction welding method. The welded joint is evaluated by visual inspection, leak-proof ability by helium leak detection testing, microstructure features by optical and scanning electron microscopy, energy dispersive x-ray spectroscope, x-ray diffraction patterns, tensile testing, and hardness measurements. The continuity of welding is evaluated by peripheral inspection and testing on four different locations of pipe welded joint. The results revealed that sound joints between dissimilar materials of Cu-SS are established with evidence of resistance to leak at room temperature and after cryogenic shock test. The Cu-SS pipe joint received excellent strength of 242.48 N/mm2, which is nearly 80% of ETP-Cu base material. The microstructure changes are distinctly observed at the Cu side, whereas no significant microstructure changes are observed at the SS side. The microstructure features are consisting of full dynamic recrystallization zone and partial dynamic recrystallization zone that are identified at the Cu side. However, no adverse effect of microstructure on tensile strength and hardness is observed. The weld continuity in the periphery of pipe configuration is observed at four different locations. A continuous reaction layer at four investigated locations is identified, with the presence of Cu and Fe elements at the joint interface.

Evolution of microstructure, texture and residual stress of AZ31 Mg alloy in hot extrusion process

In this work, we have investigated the microstructure, texture, and residual stress of AZ31 Mg alloy at several higher extrusion temperatures (360 °C, 380 °C, 400 °C) and speeds (1 m min−1, 2 m min−1, 3 m min−1). Results show that the bimodal microstructure can be observed in all extruded Mg alloys, consisting of the fine grains in dynamic recrystallization (DRX) zone and the coarse grains in non-dynamic recrystallization (non-DRX) zone. The non-monotonic relation between average grain diameter and extrusion speed has been found. It is attributed to the promoted nucleation and inhibited grain growth at higher extrusion speed. The bimodal microstructure can maintain the stability of sharp {0002} basal texture. Schmid Factor (SF) is calculated to explain the mechanism of basal texture formation. By employing XRD with cosα method, the residual stress has been measured. The major origin of residual stress release at higher extrusion temperature is the grain growth, rather than the strengthening of basal texture. The anisotropy of residual stress distribution is related to the coupling effect of grain growth and evolution of basal texture of extruded Mg alloys.

Insights into microstructural evolution and deformation behaviors of a gradient textured AZ31B Mg alloy plate under hypervelocity impact

We have for the first time elucidated the microstructural evolution and deformation behaviors of a gradient textured AZ31B Mg alloy plate under the ultrahigh strain rate of ~106 s−1 that is generated by a two-stage light gas gun with the hypervelocities of 1.6−4.4 km s−1. The hypervelocity impact cratering behaviors indicate that the cratering deformation of AZ31B Mg alloy is mainly affected by the inertia and strength of the target material. The crater prediction equation of AZ31B Mg alloy target under impact velocity of 5 km s−1 is given. The 2017Al projectile completely melts in the Mg alloy target plate at the impact velocities of 3.8 km s−1 and 4.4 km s−1, and the microstructural evolution around the crater is: dynamic recrystallization zone, high-density twinning zone, low-density twinning zone, and Mg alloy matrix. It is found that the dynamic recrystallization, twinning and cracking are the main deformation behaviors for the AZ31B Mg alloy to absorb the shock wave energy and release the stress generated by the hypervelocity impact. The main plastic deformation mechanisms of the Mg alloy target during hypervelocity impact are twinning and dislocation slip. Microstructure analysis shows the interactions of twins-twins, dislocations-dislocations, and twins-dislocations determine the strain hardening during the hypervelocity impact process, which eventually contributes the dynamic mechanical properties. The evolution of microhardness around the crater further demonstrates the microstructural evolutions and their interactions under the hypervelocity impacts.

Mechanical properties, corrosion behavior and biocompatibility of orthopedic pure titanium−magnesium alloy screw prepared by friction welding

Abstract The dissimilar joining of biodegradable magnesium alloy to pure commercial titanium by rotational friction welding with rotational speeds of 1100, 1200 and 1300 r/min for the production of bio-screw was investigated. The metallographic analysis revealed that a good joining was obtained at the Ti/Mg alloy joint. On the magnesium alloy side, various regions such as the weld center zone (WCZ), dynamic recrystallization zone (DRX), thermo-mechanically affected zone (TMAZ) and partially deformed zone (PDZ) were observed. The highest tensile and shear strengths were 173 and 103.2 MPa, respectively at a rotational speed of 1300 r/min. The Ti/Mg alloy dissimilar friction welded joint failed at the vicinity of the intermetallic zone containing Ti3Al phase. The hardness values from the base metal magnesium alloy to the joining point increased mainly due to grain refinement (8.57 μm in diameter) and the presence of titanium particles, while the hardness values were constant on the titanium side. It was also found that the corrosion rate of the Ti/Mg alloy joint was higher compared with that of the Ti and Mg alloy from the immersion studies. Additionally, the sample with a rotational speed of 1300 r/min showed better biocompatibility and a cell viability of 98.12% due to better corrosion resistance.

Thermal and mechanical induced texture evolution of inertia friction welding in α + β titanium alloy

Shear and compression textures of inertia friction welding in the welding region of the α + β titanium alloy were measured using electron backscatter diffraction. The texture of substantial remnant β in the thermo-mechanical affected zone (TMAZ) was 〈100〉 fiber texture, while, it was the 〈111〉 fiber texture in the dynamic recrystallization zone (DRZ). In the DRZ, continuous dynamic recrystallization occurred which retained the deformation texture. To summarize, we concluded that the predominant deformation in the TMAZ was compression, while that in DRZ was shear.

Rotary friction welding of AlCoCrFeNi2.1 eutectic high entropy alloy

AlCoCrFeNi2.1 eutectic high entropy alloy was rotary friction welded, and the evolution of microstructure and the mechanical properties of the resultant joints were investigated. Compared with the base material, the amount of eutectic cells in the heat-affected zone decreased slightly, while most grains were bended and elongated in thermal-mechanically affected zone. Grain refinement occurred in the dynamic recrystallization zone. At friction pressure of 200 MPa, the tensile strength and elongation of the joint reached 913.5 MPa and 12.1%, which are over 100% of the base metal, and fracture occurred at the base metal region far away from the weld center. While decreasing the friction pressure to 120 MPa or 80 MPa, the tensile strength of the joint degraded by 12.5% and the fracture occurred at the weld interface in the dynamic recrystallization zone. The interface appeared due to the inadequate plastic deformation under lower friction pressure and the sluggish diffusion of AlCoCrFeNi2.1 eutectic high entropy alloy.

Microstructure and mechanical properties of friction lap-butt welded ultra-thin galvanized steel sheets

In this study, a Lap-Butt joint (LBJ) of ultra-thin galvanized steel sheets with satisfactory joint properties had been produced by friction lap welding (FLW) using a pinless tool. The LBJ had a lap form but with the butt joint thickness and without the altitude intercept at back side. The LBJ was produced by the smooth material flow and plastic deformation of the top sheet. An interlayer consisting of Fe and Fe3Zn10 was observed at the interface. The dynamic recrystallization zone (DRZ) and heat affected zone (HAZ) were observed in the LBJs. The influences of FLW parameters on microstructural change and shear strength were investigated. The maximum fracture load of LBJ is equivalent to 95% fracture load of the base metal. The grain refinement induced by dynamic recrystallization increased the strength of top sheet.

Dynamic response and microstructure evolution of the finite steel target subjected to high velocity impact by copper explosively formed projectile

AbstractThe dynamic deformation of the finite steel target subjected to high velocity impact of copper explosively formed projectile is investigated by optical, scanning, and transmission electron microscopy. Morphology analysis of fracture surfaces indicates that the copper remainder plated to the crater wall shows extremely plastic deformation, which consists of elongated parabolic dimples, and the mild carbon steel target exhibits excellent brittle features that material fails mainly along the cleavage facets on the rear surface of target under strong impact of explosively formed projectile. In the surface of crater, the whole part of copper remainder and partial material of steel target undergoes completely dynamic recrystallization. The layer thickness of dynamic recrystallization zone, which displays an extreme plastic flow in solid state, is about 21.3 μm in steel target, and the average size of the refined grains significantly decreases to approximately 200 nm. Theoretically calculated results indicate that the temperature increase is associated with shock wave and plastic deformation of steel target and can reach 1352 K, which is 0.75Tm (where Tm is the melting temperature of steel target). The change in microhardness from the crater wall to the matrix of target is consistent with micro‐deformation of grains, and maximum microhardness is observed on the interface between dynamic recrystallization and severe plastic deformation zones of steel target.

Hot deformation behavior and processing maps of Ti–15Al–12Nb alloy

The isothermal hot compression tests of Ti–15Al–12Nb alloy under wide range of strain rates (0.01–10.00 s−1) and deformation temperatures (950, 1000, 1050, and 1100 °C) were carried out using Gleeble-3500 thermo-simulation machine. A constitutive equation represented as a function of temperature, strain rate and true strain was developed, and the hot deformation apparent activation energy is calculated to be about 453 kJ·mol−1. By employing dynamic material model (DMM), the processing maps of Ti–15Al–12Nb alloy at various strains were established. Maximum efficiency of about 57 % for power dissipation is obtained at high temperature and low strain rate. Owing to the high power dissipation efficiency and excellent processing ability in dynamic recrystallization (DRX) zone for metal material, the optimum processing conditions are selected as the temperature range of 1050–1100 °C and the strain rate range of 0.01–0.10 s−1. Using transmission electron microscopy (TEM) studies, it is found that the dislocation density is directly associated with the value of processing efficiency. It is observed that when the processing efficiency is about 22 %, the dislocation density is reasonably large. The flow instability region occurs at strain rate of 10.00 s−1 with cracks, which should be avoided during hot processing to obtain the required mechanical properties.

An Investigation into Hot Deformation Characteristics and Processing Maps of High-Strength Armor Steel

The isothermal hot compression tests of high-strength armor steel over wide ranges of strain rates (0.01-10 /s) and deformation temperatures (950-1100 °C) are carried out using Gleeble thermo-simulation machine. The true stress-strain data obtained from the experiments are employed to establish the constitutive equations based on the strain-compensated Arrhenius model. With strain-compensated Arrhenius model, good agreement between the experimental and predicted values is achieved, which represents the highest accuracy in comparison with the other models. The hot deformation activation energy is estimated to be 512 kJ/mol. By employing dynamic material model, the processing maps of high-strength armor steel at various strains are established. A maximum efficiency of about 45% of power dissipation is obtained at high temperature and low strain rate. Due to the high power dissipation efficiency and excellent processing ability in dynamic recrystallization zone for metal material, the optimum processing conditions are selected such that the temperature range is between 1050 and 1100°C and the strain rate range is between 0.01 and 0.1/s. Transmission electron microscopy observations show that the dislocation density is directly associated with the value of processing efficiency.

Investigation of Hot Deformation Characteristics of AISI 4340 Steel Using Processing Map

Uniaxial compression tests at various temperatures from 850°C to 1200°C and strain rates between 0.01 s-1 and 10 s-1 were carried out in order to determine hot working characteristic of the AISI 4340 steel. The plastic stress-strain responses at high temperatures of the steel were provided. Constitutive relationship between the flow stresses and the Zener–Hollomon parameters was primarily established by means of a hyperbolic sine function for the entire range of the investigated conditions. Afterwards, the power dissipation map and instability map were developed on the basis of the Dynamic Materials Model (DMM). The variation of efficiency of the power dissipation calculated as a function of strain rate sensitivity represented material behaviors according to the microstructure evolution. The peak efficiency indicated an optimum processing window for hot working. In this study, processing map was obtained by a superimposition of the power dissipation and the instability criterion. The domains of temperature and strain rate, in which material flow stability occurred, were determined. For the AISI 4340 steel, the processing maps exhibited a distinct domain with its peak efficiency at about 1050-1200°C and 0.01-0.1 s-1, in which the peak efficiencies of about 40-50% were shown for different strains. In combination with microstructure observations after hot deformation, dynamic recrystallization zone could be identified in the processing map at a certain strain.

Experimental Investigation of Fatigue Crack Growth in the Welding Nugget of FSW Joints of a 6060 Aluminum Alloy

The work investigates the fatigue behavior of friction stir welded butt joints by means of fracture mechanics techniques. FSW joints of artificially aged AA6060 T6 aluminum alloy were studied. The welding was performed on 8 mm thick butt joined sheets by means of a CNC machine tool. Welding speed in the range between 117 and 683 mm/min and tool rotational speed between 838 and 1262 rpm were considered. Fatigue crack growth tests were performed according to ASTM E647 standard on CT specimens, under constant load amplitude conditions, at 0.1 minimum to maximum load ratio, with the notch placed in the dynamic recrystallization zone of weld nugget, oriented along the welding direction. The comparison of results demonstrates the crack growth rate is always equal or lower than the base material at low values of stress intensity range. At ΔK values above 12 MPa√m, crack growth rate was found to be higher than base material for high feed, low speed and high feed/speed ratio.