Continuous Extrusion Forming Research Articles

Modification and strengthening of recycled Al-Mg-Si-based alloy upon continuous rheological extrusion (CRE) forming

With global warming and resource scarcity, it is crucial to devise a simple, energy-efficient, and low-emission recycling method for aluminum alloys. In the recycled Al-Mg-Si-based alloy, the coarse α-Al dendrites, the long plate-like β-Al5FeSi phase and bulk Mg2Si phase significantly impair the microstructure and mechanical properties of the alloys. In this works, combined the continuous rheological extrusion (CRE) technology with the addition of CRE Al-5.0Ti-1.0B (wt%) refiner, the recycled Al-Mg-Si-based alloy wires at extrusion ratios (ER) of 3, 5 and 7 were prepared. The refinement of Mg2Si and β-Al5FeSi phases and the grain refinement caused by the continuous dynamic recrystallization (CDRX) behavior in the CRE process were discussed. The strengthening mechanism of recycled Al-Mg-Si-based alloy was revealed. The results showed that, CRE technology and CRE Al-5.0Ti-1.0B (wt%) refiner can effectively refine Mg2Si and β-Al5FeSi phases, and even to the nanometer level. At the same time, the increase of ER and the addition of CRE Al-5.0Ti-1.0B (wt%) can promote the transformation of low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs), thereby promoting the occurrence of CDRX. In addition, the increase of dislocations and nanophases caused by the increase of ER and the addition of CRE Al-5.0Ti-1.0B can effectively refine CDRX grains. When 0.2 wt% CRE Al-5.0Ti-1.0B (wt%) refiner was added at ER of 7, the ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of recycled Al-Mg-Si-based alloy were 259.40 MPa, 140.80 MPa and 18.20%, respectively. Grain boundary strengthening and dislocation strengthening were the primary mechanisms in enhancing the YS of the recycled Al-Mg-Si-based alloy.

Microstructural Evolution and Mechanical Properties of a Continuously Cast Al–Mg–Si–Cu Alloy Processed by Repetitive Continuous Extrusion Forming

Microstructural Evolution and Mechanical Properties of a Continuously Cast Al–Mg–Si–Cu Alloy Processed by Repetitive Continuous Extrusion Forming

Microstructural evolution and strengthening mechanism of Al–Mg alloys with fine grains processed by accumulative continuous extrusion forming

• The response of mechanical property to the microstructure variation was analyzed. • The grain refinement induced by CDRX and secondary phases was illustrated. • The strengthening mechanism caused by microstructure evolution was revealed. • A strategy to produce Al–Mg alloys with high mechanical performance was provided. In this work, the mechanical properties and strengthening mechanisms induced by microstructural evolution in a rheo-extruded 5087 alloy processed via accumulative continuous extrusion forming (ACEF) were investigated. Electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) were utilized to characterize the microstructure of the alloy subjected to ACEF with various passes. The grain refinement caused by continuous dynamic recrystallization (CDRX) was discussed. The results demonstrated that after 3 passes of ACEF, there was a significant grain refinement effect on the alloy, and the average grain size decreased from 45.6 μm to 2.5 μm; the ultimate tensile strength (UTS) and yield strength (YS) of the alloy increased to 362.8 MPa and 234.6 MPa, respectively. Dislocation cells/walls generated during deformation promoted the formation of low angle grain boundaries (LAGBs). The accumulative strain accelerated the transformation of LAGBs to high angle grain boundaries (HAGBs). Dislocation pile-up enhanced the driving force of CDRX, and nano-sized Al 6 (Mn, Fe) phases at the grain boundaries inhibited the growth of grains due to the pinning effect. Based on the quantitative estimation, dislocation strengthening and grain boundary strengthening dominated the enhancement in YS of the ACEFed alloy.

Enhanced electrical, mechanical and tribological properties of Cu-Cr-Zr alloys by continuous extrusion forming and subsequent aging treatment

• A high performance Cu-1Cr-0.1Zr alloy was obtained by continuous extrusion forming and subsequent aging treatment. • The strengthening contributions of the grain refinement, dislocation and precipitation were quantitatively calculated. • The wear behavior was studied by examining the evolution of wear surface morphology and subsurface microstructure. • The microhardness (H), H/E r ratio and H 3 /E r 2 ratio were considered to gage the wear resistance of Cu-Cr-Zr alloy. As a promising material for the new generation of high-speed railway contact wires, the comprehensive optimization of the electrical conductivity, strength, hardness and wear resistance of the Cu-Cr-Zr alloy has received extensive attention. In this paper, a high-performance Cu-1Cr-0.1Zr alloy with an ultimate tensile strength of 599.1 MPa, a uniform elongation of 8.6%, a microhardness of 195.7 HV 0.2 and an electrical conductivity of 80.07%IACS was achieved by the continuous extrusion forming (CEF) and subsequent peak-aging treatment. The grain refinement strengthening, dislocation strengthening and precipitation strengthening are identified to be responsible for the excellent electrical and mechanical properties of Cu-Cr-Zr alloy. The wear behavior of Cu-Cr-Zr alloy was investigated by examining the evolution of worn surface morphology and subsurface microstructure. The microhardness ( H ) and reduced elastic modulus ( E r ) of the subsurface below the worn surface measured by nanoindentation were calculated to gage the tribological performance of Cu-Cr-Zr alloy. Results show that the continuously extruded and subsequently peak-aged specimen has the best wear resistance, which indicates that the tribological properties of Cu-Cr-Zr alloy strongly depend on its strength and hardness. It can be concluded that the CEF and subsequent aging treatment process provides a new and high-efficiency procedure for the continuous preparation of Cu-Cr-Zr alloys.

Mechanisms of primary phase refinement and toughness improvement of Cu–2 wt% Ag–0.15 wt% La alloy through continuous extrusion forming

A new Cu–2 wt% Ag–0.15 wt% La alloy composed of large-size Ag-rich primary phases was processed into wire billets by successive drawing, annealing and continuous extrusion forming (CONFORM). The microstructural evolution and mechanical properties of the samples obtained by drawing, annealing and CONFORM were then investigated. The results indicate that a desirable combination of high ultimate tensile strength (300 MPa) and elongation (49.5%) was obtained after CONFORM. The latter allowed the microstructure to be significantly refined via an almost full dynamic recrystallization (DRX), with grain sizes of ~ 1 μm. In addition, the large-size primary phases were broken into dispersed nanophases with an average size of 800 nm. The dispersed phases promoted the DRX of the matrix via particle-stimulated nucleation. As a result, the enhanced toughness (11145.98 MPa·%) is contributed by grain refinement and dispersion strengthening of the nanosized phases.

High electrical conductivity Al-Ag-Sc-Zr alloy with ultrafine grains processed by accumulative continuous extrusion

Continuous preparation of high-conductivity and high-strength aluminium alloy cable remains a challenge. Here we reveal the scientific significance of high electrical conductivity Al-Ag-Sc-Zr alloy with ultrafine grains prepared by novel processing technologies, the combination of rheo-extrusion and accumulative continuous extrusion forming. Attributed to the continuous dynamic recrystallization during rheo-extrusion, equiaxial microstructure and significantly refined grains (2.8 ± 0.2 μm) were achieved. By means of partially replacing low conductive scandium and zirconium solute atoms with high conductive silver solute atoms, the processed alloy wires exhibit significant higher electrical conductivity (53.5 ± 0.4 %IACS) than the Al-Sc-Zr alloy with similar atomic concentration of alloying elements. Appropriate mechanical properties were also obtained due to the similar solution strengthening effects of silver atoms to scandium and zirconium atoms. These results highlight the potential of this high electrical conductivity Al-Ag-Sc-Zr alloy and its novel processing route.

Microstructural Evolution of Al-1Fe (Weight Percent) Alloy During Accumulative Continuous Extrusion Forming

As a new microstructure refining method, accumulative continuous extrusion forming (ACEF) cannot only refine metal matrix but also refine the phases that exist in it. In order to detect the refinements of grain and second phase during the process, Al-1Fe (wt pct) alloy was processed by ACEF, and the microstructural evolution was analyzed by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Results revealed that the average grain size of Al-1Fe (wt pct) alloy decreased from 13 to 1.2 μm, and blocky Al3Fe phase with an average length of 300 nm was granulated to Al3Fe particle with an average diameter of 200 nm, after one pass of ACEF. Refinement of grain was attributed to continuous dynamic recrystallization (CDRX), and the granulation of Al3Fe phase included the spheroidization resulting from deformation heat and the fragmentation caused by the coupling effects of strain and thermal effect. The spheroidization worked in almost the entire deformation process, while the fragmentation required strain accumulation. However, fragmentation contributed more than spheroidization. Al3Fe particle stimulated the formation of substructure and retarded the migration of recrystallized grain boundary, but the effect of Al3Fe phase on refinement of grain could only be determined by the contrastive investigation of Al-1Fe (wt pct) alloy and pure Al.

Microstructure Evolution of Copper Strip during Continuous Extrusion and Rolling Forming

During the continuous extrusion and rolling forming process, the microstructure evolution of copper strip was investigated by the optical microscope and transmission electron microscope. The results indicated that the grains in the centre of as-cast rod billet were squashed in the clamping zone and were elongated in the rigid mobile zone. The fibrous structure formed in the upsetting zone. In the adhesion zone, the dynamic recrystallization occurred and the shear band was found. In the right-angle bending zone, the fibrous structure, recrystallized grains and shear bands existed together. The full dynamic recrystallization occurred in the extending extrusion zone. After continuous extrusion forming, the size of the grains of copper strip was larger than that in the extending extrusion zone. After rolling, the grains in copper strip were evidently stretched along the rolling direction, which resulted in the formation of stable direction. With the increase of rolling reduction, the grains were squashed gradually. When the rolling reduction increased from 2 to 6 mm, the tensile strength increased from 250 to 400 MPa, and the elongation decreased from 48% to 13%.

Effect of Billet Preheating Temperature on Continuous Extrusion Forming of Al-Sr Alloy

Abstract Based on numerical simulation and process experiment, this study investigates the effect of billet preheating temperature on continuous extrusion forming of Al-Sr alloy and the microstructure and mechanical properties of products. The numerical simulation results show that the temperature starts to rise after the billet enters into the cavity during the continuous extrusion of Al-Sr alloy, and the maximum temperature appears at the die exit. Moreover, the maximum equivalent stress appears in the right-angle bending zone. The billet preheating temperature increases from 300 °C to 480 °C, the maximum temperature of billet in cavity increases from 483 °C to 512 °C and the temperature at the die exit increases from 493 °C to 522 °C. The experiment results show that the Al4Sr phase morphology in products changes from granular to blocky and increases in size. The tensile strength decreases from 114 MPa to 104 MPa, and the elongation increases from 8.4% to 10.5%.

Microstructures and Properties of Aluminum Alloys during Repetitive Continuous Extrusion Forming

Repetitive continuous extrusion forming was employed as a continuous severe plastic deformation route and both Al-Fe-Cu alloy and Al-Mg-Si alloy were involved. Evolution of microstructures and properties during this process is investigated by optical microscope, electron-backscatter diffraction, transmission electron microscope, and tensile testing. The results show that in the Al-Fe-Cu alloy an obvious mechanical softening and grain refinement were observed, while in the Al-Mg-Si alloy it shows a slightly rising in strength and ductility as the extrusion passes increasing.

The effects of eutectic silicon on grain refinement in an Al–Si alloy processed by accumulative continuous extrusion forming

Grains of Al–1Si(wt%) alloy were refined by accumulative continuous extrusion forming (ACEF). Electron backscatter diffraction and transmission electron microscopy were used to analyze the microstructure evolution of the Al–1Si(wt%) alloy. The grain size of the alloy decreased from 54.36 to 2.59 μm after four passes of ACEF. The grain refinement was attributed to continuous dynamic recrystallization (CDRX). The enhanced effect of nanosized precipitates on CDRX was pronounced. Nanosized eutectic Si precipitates retained a high density of dislocations in the alloy by promoting their generation and pile-up, resulting in an increase in the driving force for CDRX and a consequent promotion of grain refinement. After 4 ACEF passes, the tensile yield strength of the alloy at room temperature increased from 102 MPa to 117 MPa. Further, the elongation of the alloy at room temperature decreased from 38 to 17 % after 3 ACEF passes and subsequently increased to 23 % after 4 ACEF passes.

Microstructural Characteristic of the Al-Fe-Cu Alloy During High-Speed Repetitive Continuous Extrusion Forming

High-speed repetitive continuous extrusion forming process (R-Conform process) was performed on the Al-Fe-Cu alloy. The microstructural evolution and mechanical properties were studied by x-ray diffraction, electron backscatter diffraction, transmission electron microscopy and tensile testing. The results show that a significant improvement of tensile ductility concurs with a considerable loss of tensile strength before four passes, after that the process on mechanical properties variation tends to be steady, indicating an accelerated mechanical softening occurs when comparing to low-speed R-Conform process. Microstructure characterization indicates that the accumulated strain promotes the transformation of low angle boundaries to high angle boundaries, thus leading to the acceleration of continuous dynamic recrystallization process, and the precipitates are broken, spheroidized and homogeneously distribute in Al matrix as increasing R-Conform passes. Massive microshear bands are observed after initial passes of R-Conform process, which may promote continuous dynamic recrystallization and further grain refinement during high-speed R-Conform process.

Microstructure and Properties of 7075Al Alloy Fabricated by Directly Combined of Spray Forming and Continuous Extrusion Forming under Different Atomization Gas Pressures

A new process consisting of the spray forming and the continuous extrusion forming for manufacturing 7075Al alloy was proposed. The microstructure evolution, mechanical properties and the resistance to stress corrosion cracking of the alloy were studied. The results indicate that the spray forming process induces obviously grain refinement and greatly lower segregation microstructure. Besides, the Conform process produces finer grains and conduces to more uniform distribution of the precipitates of AlCu and MgZn2 phases. The fabricated alloy shows good comprehensive mechanical properties and superb performance of stress corrosion resistance. Moreover, a better combination of the mechanical properties and the resistance to stress corrosion cracking could then be obtained under a certain condition of atomization gas pressure of 0.19 MPa. The enhanced properties are attributed to the following factors, which include the grain refinement, the fine and homogeneous distribution of AlCu and MgZn2 phases, the high density of the extruded products, as well as the discontinuous distribution of the grain boundaries after retrogression and reaging (RRA) heat treatment.

Grain refinement in an Al[sbnd]Er alloy during accumulative continuous extrusion forming

The grain of an Al0.2Er alloy (wt%) was refined by accumulative continuous extrusion forming (ACEF). Microstructure of the AlEr alloy subjected to ACEF was investigated through electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results revealed that the formation of ultra-fine grains results from a type of continuous dynamic recrystallization (CDRX) that is induced by large strains. With the accumulation of strain, LAGBs gradually introduced and transformed into HAGBs, which leads to an increase in the average orientation angle. The micro-grain alloy is refined through repeated passes of the continuous extrusion forming process and the average grain size of the Al0.2Er (wt%) alloy decreased from 26.01 μm to 1.3 μm in four passes. The Al0.2Er (wt%) alloy had a smaller average grain size than that of pure aluminum. The formation of precipitates in AlEr alloy can stimulate the nucleation of CDRX by increasing the local strain energy and slow the growth of recrystallization grains by limiting grain boundary migration that causing grain refinement.

Continuous extrusion and rolling forming of copper strips

Continuous extrusion and rolling technology was proposed as a new strip production technology. It conducts a hot rolling process using waste heat after continuous extrusion. The continuous extrusion and rolling forming was simulated with DEFORM-3D T . Influences of extrusion wheel velocity and rolling reduction on the continuous extrusion and rolling forming were analyzed. It was shown that as extrusion wheel velocity increases, torque of extrusion wheel, chamber force and rolling force, will drop; temperature of the billet in the area of abutment which is highest will increase. As the rolling reduction is increased, torque of the extrusion wheel and force acting on the chamber decrease, while torque and force of the rolls increase. The experimental results showed that a homogeneously distributed and equiaxed grains microstructure can be formed in copper strip billets with an average grain size of about 80 μm, after continuous extrusion. Grains of the copper strips are stretched clearly, during rolling, along the rolling direction, to form a stable orientation. Nevertheless, the grain boundaries are still relatively clear to see.

Microstructures and properties of Al–Mg–SI alloy overhead conductor by horizontal continuous casting and continuous extrusion forming process

Al–Mg–Si alloy overhead conductor was prepared by horizontal continuous casting and subsequent continuous extrusion forming. The mechanical properties, electrical conductivity and microstructural evolution of the processed conductor were characterized. It was indicated that improved combined mechanical and electrical conductivity properties were obtained for the processed alloy wires when compared with previously reported results. The enhanced properties were associated with the continuous in-line solution treatment and the refined and homogeneous (sub)grains during horizontal continuous casting and subsequence continuous extrusion forming, as well as a high density of dislocations and finer Mg2Si precipitates formed after drawn and followed by aging at 155°C for 3h.

Microstructure and properties of Al–0.70Fe–0.24Cu alloy conductor prepared by horizontal continuous casting and subsequent continuous extrusion forming

A novel process for manufacturing Al–0.70Fe–0.24Cu alloy conductor was proposed, which includes horizontal continuous casting and subsequent continuous extrusion forming (Conform). The mechanical properties, electrical conductivity and the compressed creep behaviour of the alloy were studied. The results indicate that the Conform process induces obvious grain refinement, strain-induced precipitation of Al7Cu2Fe phase and the transformation of crystal orientation distribution. The processed alloy has good comprehensive mechanical properties and electrical conductivity. Moreover, a better creep resistance under the conditions of 90 °C and 76 MPa is shown compared with pure Al and annealed copper, and the relationship between primary creep strain and time may comply with the logarithmic law. The enhanced properties are attributed to the grain refinement as well as the fine and homogeneously distributed thermally stable AlFe and Al7Cu2Fe precipitation phases.

Continuous extrusion and rolling forming technology of copper strip manufacture

Continuous extrusion and rolling technology was proposed as a new strip production technology. It finished hot rolling process using the waste heat of the continuous extrusion forming. The continuous extrusion and rolling forming process was simulated by DEFORM-3DT software. The influence of extrusion wheel velocity and strip size on the continuous extrusion and rolling forming process was analyzed. The experiment was carried out according to optimized results of numerical simulation, the microstructure and property of copper strip were fine.

Microstructures and mechanical properties evolution of an Al–Fe–Cu alloy processed by repetitive continuous extrusion forming

Repetitive continuous extrusion forming process (R-Conform process), as a continuous severe plastic deformation method, was performed on a horizontal continuous casting Al–0.74Fe–0.23Cu alloy. The microstructural evolution and mechanical properties were studied by optical microscope, X-ray diffraction, scanning electron microscope, transmission electron microscope, and tensile testing. The results show that tensile ductility of the Al–0.74Fe–0.23Cu alloy is greatly improved but tensile strength is gradually decreased after repetitive Conform processing. The necking is more intense and the size of dimples becomes bigger with increasing Conform passes. The first pass Conform process induces obviously grains refining, dissolution of AlFe, AlFeSi and AlSi primary phases, strain-induced precipitation and transformation of crystal orientation distributions, but further Conform deformation only changes the redistribution of precipitates. The changes of mechanical properties may be attributed to a complex progress of recovery, recrystallization and redistribution of precipitates during repetitive Conform process.

Microstructure and Mechanical Properties of a CuCrZr Welding Joint After Continuous Extrusion

The effect of continuous extrusion forming (CEF) process on the microstructure and mechanical properties of a CuCrZr welding joint was investigated. The experimental results showed that after the CEF process the grains were refined to submicron-scale through dynamic recrystallization, which improved the mechanical properties of the welding joint as well as the base material. Meanwhile, the micron-scale precipitates aggregated at the grain boundaries in the welding process were broken down to smaller ones and recrystallized grains of several micrometers formed around the precipitates after CEF process, which could alleviate the negative effect induced by the micron-scale precipitates during plastic deforming process. Finer grains and smaller micron-scale precipitates made contributions to improve the properties of a CuCrZr alloy with a welding joint.