Higher Extrusion Ratio Research Articles

Effect of High Deformation without Preheating on Microstructure and Corrosion of Pure Mg

In this study, the relationship between the extrusion ratio and the corrosion resistance of pure Mg deformed using extrusion with an oscillating die (KoBo) without preheating of the initial billet was investigated. The materials investigated in this study were extruded at high deformation ratios, R1 5:1, R2 7:1, and R3 10:1, resulting in significant grain refinement from the very coarse grains formed in the initial billet to a few µm in the KoBo-extruded samples at room temperature, which is not typical for hexagonal structures. Our research clearly shows that KoBo extrusion improves the corrosion performance of pure Mg, but there is no straightforward dependence between the extrusion ratios and corrosion resistance improvement. Although it was expected that the smallest grain size should provide the highest corrosion resistance, the dislocation density accumulated in the grain interiors during deformation at the highest extrusion ratio, R3 10:1, supports dissolution reactions. This, in turn, provides the answers for the greater grain size observed after deformation at R2 7:1, where dynamic recovery prevailed over dynamic recrystallization. This situation led to the annihilation of dislocation, leading to better corrosion resistance of the respective alloy. Therefore, the alloy with the greatest grain size has the best corrosion resistance.

High Mechanical Property and Texture Degree of Hot-Extruded Bi0.905Sb0.095

Bi1−xSbx crystal is one of the best n-type thermoelectric materials below 200 K, but its weak mechanical strength hinders practical applications for deep refrigeration. Herein, we adopted the mechanical enhancement method of hot extrusion to investigate the comprehensive mechanical and thermoelectric properties of Bi0.905Sb0.095. It revealed that reducing the grain size of the matrix and increasing the extrusion ratio can improve the gain size uniformity and mechanical properties. Meanwhile, the thermoelectric performance depends on the texture, grain size, and local composition. The extruded sample prepared by ingot with the high extrusion ratio of 9:1 generated uniform small grains, which resulted in the high bending strength of Bi1−xSbx~130 Mpa and a high power factor of ~68 μW·cm−1·K−2@173 K, as well as the relatively high figure of merit of 0.25@173K. This work highlights the importance of the uniform distribution of the grain size and the compositions for Bi1−xSbx, as well as the required universal key parameter for the hot extrusion method.

Study on the microstructure and mechanical properties of VW73B alloy at high extrusion ratio

The microstructure and mechanical characteristics of VW73B prepared by a high extrusion ratio (70:1) were studied. High-strength plastic VW73B alloy containing long-period structural phase (LPSO) was obtained by extrusion process. OM, SEM, TEM, and EBSD were used to investigate the relationship between microstructure and mechanical characteristics of VW73B. The findings indicate that VW73B presents complete dynamic recrystallization after deformation, and there are 14H-LPSO phases, SFs, and a large amount of β´ phase, which are precipitated after aging treatment. The UTS, YS, and EL of VW73B in peak aging state are 406 MPa, 339 MPa, and 9%, respectively. The β´ phase, LPSO phase, poor texture, and fine grain strengthening of VW73B contribute to its exceptional characteristics.

Analysis of the influence of dies geometry on the process extrusion force and properties of the extrudate obtained in the process of cold extrusion of 7075 aluminum alloy by the KOBO method

Abstract The KOBO extrusion process is an unconventional method of extrusion based on the phenomenon of superplasticity as an effect of a special state caused by the oscillatory motion of the die at a certain angle a certain frequency. It significantly lowers the extrusion force and makes it possible to extrude lightweight metals and alloys (e.g. aluminum and magnesium alloys) in cold extrusion with high extrusion ratios compared to conventional hot extrusion. This work studies the influence of the tool (die) geometry on process realization parameters and the properties of the extrudate. Experimental studies of cold KOBO extrusion were performed using dies with different face portion geometry. The obtained extrudate obtained from EN-AW 7075 aluminum billets was examined for mechanical properties and macro/microstructure, showing that, with adequate modifications to the tool face part geometry, it is possible to lower the extrusion force and obtain extrudate with desired properties.

Evolution of grain characteristics and dynamic recrystallization behavior of Cu–15Ni–8Sn alloy under different extrusion ratios

For atmospheric melting cast Cu–15Ni–8Sn alloy, hot extrusion tests were conducted on ingots of Cu–15Ni–8Sn alloy with varying extrusion ratios (5, 12 and 16) following homogenization and annealing. The investigation employed mechanical property tests, scanning electron microscopy and transmission electron microscopy to analyze the mechanical characteristics, dynamic recrystallization and twinning behaviors of the alloys subjected to different extrusion ratios. The findings revealed a reduction in the average grain size of the alloy as the extrusion ratio increased. The alloy undergoes dynamic recrystallization during hot extrusion, and the degree of recrystallization of the alloy escalated with higher extrusion ratios. The alloy underwent completely recrystallized at an extrusion ratio of 16, primarily driven by discontinuous dynamic recrystallization (DDRX). In addition, the alloy generated twins during the DRX process, and the twin boundaries provided favorable sites for the nucleation of DRX grains, which promoted the DRX of the alloy. Notably, at an extrusion ratio of 16, the alloy demonstrated impressive mechanical properties, with an ultimate tensile strength of 836 MPa and an elongation of 13.5 %. These results presented a substantial enhancement, showcasing a 54 % increase in the extruded ultimate tensile strength and a 350 % increase in the elongation compared to that of the alloy in the homogenized annealed state.

Microstructural, corrosion and mechanical properties of a WE43 alloy: conventional extrusion versus SPD

A hexagonal close-packed-structure WE43 alloy was extruded without any preheating of the initial billet using extrusion with an oscillating die to improve the corrosion and mechanical properties. The WE43 alloy was extruded at high ratios of R1 5:1, R2 7:1 and R3 10:1. Electron back-scatter diffraction and transmission electron microscopy were used to determine the microstructural properties of the alloys. The influence of the extrusion method and the extrusion ratios on the corrosion and mechanical properties were investigated. Electrochemical tests were performed, and the corrosion damage was inspected. Tensile tests were made using micro specimens. When compared to conventional extrusion, the microstructural changes obtained with the KoBo method at R1 5:1 increased the corrosion resistance, which was not only due to the grain refinement, but also due to the intensity of the texture. A decline in the corrosion resistance of the alloys deformed at higher extrusion ratios was observed. This was a result of the massive plastic strain imposed by the KoBo die. The room-temperature mechanical properties of the KoBo-extruded alloys were improved. However, at higher temperatures the mechanical properties decreased due to the solutioning of tiny triple precipitates.

Effect of extrusion parameters on microstructure and mechanical properties of Mg–6Zn–1Mn–0.2Gd alloy

The microstructure, dynamic recrystallization behavior and texture evolution of an as-extruded Mg–6Zn–1Mn–0.2Gd (ZMG610) alloy at different extrusion conditions (extrusion ratios of 25 and 45, temperatures of 350 and 400°C) were investigated. The as-cast ZMG610 alloy was mainly composed of the α-magnesium (α-Mg) matrix, the Mg7Zn3 phase and Mg3Zn6Gd (I phase). A large number of I-phase particles remained in the matrix after homogenization treatment at 330°C up to 24 h. The as-extruded ZMG610 alloy exhibited a bimodal structure consisting of fine dynamically recrystallized grains with a wide orientation spread and coarse undynamically recrystallized grains with a strong basal texture. All as-extruded samples exhibited a typical basal texture with the basal plane of most grains parallel to the extrusion direction. A lower texture intensity could be obtained by increasing both the extrusion ratio and temperature. Optimal mechanical properties (yield strength of 267 MPa, ultimate tensile strength of 360 MPa and elongation of 14.2%) were obtained through the combination of a low temperature (350°C) and a high extrusion ratio (45). Amelioration of mechanical properties highly depended on the synergistic effect of dynamically recrystallized grains, I-phase particles and texture.

Ultrathin aluminum-graphite composite foil with high thermal conductivity prepared by hot-extrusion technique

Heat dissipation film/ foil materials with high thermal conductivity in the through-plane direction are in high demand for improving the heat dissipation in the integrated circuits (IC) with high level of integration. In this letter, ultrathin aluminum-graphite (Al-Gr) composite foil with high through-plane thermal conductivity (46 W/m·K) was fabricated using the hot-extrusion technique. Specifically, the ultrathin Al-Gr composite foil was obtained through a high extrusion ratio (∼13:1) using the Al-Gr cylinder, during which the graphite sheets act as an effective self-lubrication media. The high through-plane thermal conductivity of the ultrathin Al-Gr composite foil is attributed to the coupled effects of the clean and tight interfacial bonding state between the Al and graphite sheets as well as the interconnected graphite sheets in the through-plane direction. Ultrathin Al-Gr composite foil with high through-plane thermal conductivity is expected as a competitive candidate for enhancing the heat dissipation capacity of the IC system.

Role of dynamic recrystallization and grain growth on the formation of abnormal basal texture in a high-alloyed Mg-Al-Zn extruded alloy

A commercial Mg-8.1Al-0.58Zn-0.27Mn alloy (mass%, AZ80) was extruded using different temperature and extrusion ratio. The microstructural development was thoroughly investigated by electron backscatter diffraction. A typical basal texture with the vertical alignment of the (0001) poles to the extrusion direction became main texture component regardless of the extrusion conditions. Notably, dynamically recrystallized grains, which had the parallel alignment of the (0001) poles to the extrusion direction, were formed at the initial stage of extrusion. However, such abnormally textured grains were consumed by basal-textured grains when the extrusion was performed at a relatively low temperature or using a high extrusion ratio of 50. In contrast, apparent intensity corresponding to the abnormal texture component was preserved during the extrusion at 400 °C using a relatively low extrusion ratio of 10. The low extrusion ratio facilitated the growth of the abnormally textured grains, which maintained a certain amount of the texture component having the parallel alignment of the (0001) poles to the extrusion direction.

Appearance of textures with a c-axis parallel to the extrusion direction in Mg alloys

The appearance of an unusual texture with the crystallographic c-axis parallel to the extrusion direction (‘C-texture’) occurs in bands in extruded and fully recrystallized Mg-6.5Zn alloy. This texture was previously only reported in rare-earth-containing Mg alloys. Based on our results and the available literature, it seems that this texture requires heavy alloying, and it is not linked exclusively to the presence of second phase particles. Moreover, it appears to be associated with higher extrusion ratios. Also, the starting texture seems not essential for its formation. The most likely mechanism would be the promoted pyramidal <c+a> slip stimulated by high solute levels that provides the necessary lattice rotation, along with the easy activation of prismatic <a> slip.

Effect of extrusion ratios on hardness, microstructure, and crystal texture anisotropy in pure niobium tubes subjected to hydrostatic extrusion

Nb tubes were fabricated through hydrostatic extrusion at extrusion ratios of 3.1 and 6.1 at ambient temperature, and then their microstructure, texture, and Vickers hardness were investigated based on electron back-scattered diffraction (EBSD) data. The fraction of low-angle boundaries (LABs) largely decreased with a sharp decrease in mean grain sizes after hydrostatic extrusion and was not proportional to extrusion ratios, assuming that mixed-asymmetrical junctions forming LABs dissociate at high extrusion ratios from the external stress (>981 MPa) with thermal activation by the generated heat. The correlation between grain size and Vickers hardness followed the Hall−Petch relationship despite the texture gradient of the 〈111〉 cyclic fiber textural microstructure at low extrusion ratios and the 〈100〉 true fiber textural microstructure at high extrusion ratios. The increase in hydrostatic pressure on the Nb tubes contributed to texture evolution in terms of extrusion ratios due to the difference between {110}〈111〉 and {112}〈111〉 components based on EBSD data.

Microstructural Stability of Extruded Mg-Mn-Ce Hollow Profiles with Weld Seams

Despite aluminum profiles, magnesium profiles have not been well developed due to the low formability. Furthermore, extruded magnesium profiles show a strong dependence on the mechanical properties, according to the loading direction. This is caused by a strong basal texture, which is directly dependent on the process parameters during the extrusion and the subsequent aging. Thus, the present paper focuses on the analysis of the microstructure and its evolution of extruded magnesium hollow profiles, which were subjected to a series of heat treatments at 475 °C up to one hour. The hollow profiles were extruded through a porthole die, thus, containing longitudinal weld seams. These were formed by material that underwent heavy shearing along the tool surface based on the friction conditions in the porthole die. Three extrusion ratios (ER = 8:1, ER = 16:1, ER = 30:1) were applied, resulting in three different wall thicknesses of the profiles. The microstructure of the profiles was analyzed using light-optical microscopy (LOM) and scanning electron microscopy (SEM) coupled with electron backscatter diffraction (EBSD). The analysis revealed no change of the microstructure of the profiles extruded at the two higher extrusion ratios within the time frame of the heat treatment. In contrast, the microstructure and, thus, the micro-texture of the profile with the lowest extrusion ratio (ER = 8:1) has been affected to a great extent. While only small changes in microstructure in the weld-free area were observed, the initial microstructure in the weld seam was transformed from fine recrystallized grains into a significantly bimodal microstructure mainly due to an abnormal grain growth (AGG). These changes were accompanied by a promotion of the rare-earth (RE) texture component for the weld-free material and a change of the overall texture from RE to a typical non-RE double fiber texture for the weld seam due to the intense AGG within the short-time heat treatments. In addition, the influence of the extrusion ratio on particle size and distribution as well as the character of the microstructure governing the behavior during heat treatments was analyzed and discussed.

Energy Consideration in the Microextrusion of Aluminum Alloy 6063

Abstract This paper investigated key factors influencing energy consumption in the microextrusion process. The considered factors were: extrusion ratio (ER), die angle (α), billet length (BL), bearing length (LB), coefficient of friction (COF), and die shift (DS). The finite element simulation was carried out to determine the extrusion energy required to complete one extrusion cycle. The simulation results showed that the increased values of all the considered factors (except the die shift) led to increased extrusion energy. The results also provided percentages of energy variation in steps, which helped evaluate the energy savings with regards to the crucial other production considerations. The percentage increase in energy consumption in the lower ER values was considered higher than those of, the higher ER values. Increasing die angle (α) from 60 to 90 deg barely affected the consumed energy. The highest increase percentage of extrusion energy was found while increasing billet lengths (BL) from 3.00 mm to 4.00 mm. The lower bearing length (LB) values offered lower consumed energy. The consumed extrusion energy linearly increased with COF. The die shift (DS) did not affect the extrusion energy, but the final part geometry (curved pins). The results and analysis from this study could be used to potential energy savings and overall production costs of the microextrusion process.

Carbon nanotubes reinforced aluminum matrix composites with high elongation prepared by flake powder metallurgy

High elongation aluminum matrix composites reinforced with carbon nanotubes (CNTs) were prepared by flake powder metallurgy, and densified by hot extrusion with a high extrusion ratio. After hot extrusion, fine and equiaxed grains were obtained in 2 wt% CNT/Al composite, and interfacial product (Al4C3) as well as bridge-connected CNTs aligned along the extrusion direction were found both in 1 wt% CNT/Al and 2 wt% CNT/Al composites. Both composites obtained high elongation while their strength was enhanced. Especially the elongation of 2 wt% CNT/Al composite is comparable to that of pure Al prepared by the same method, which reached about 30%. The good ductility mainly attributes to firm interfacial combination between CNTs and matrix, fine and equiaxed grains formed by dynamic recrystallization during hot extrusion, and bridge-connected CNTs aligned along the extrusion direction.

Microstructural Characteristics and Mechanical Properties of a Novel Extruded Dilute Mg–Sn–Mn–Ca Alloy

A novel dilute Mg-Sn-Mn-Ca (TMX) alloy system was developed and subjected to extrusion with a relatively high extrusion ratio of 36. The grain structure, nanoscale precipitates, texture, and tensile properties of the extruded dilute alloy were investigated. The results indicated that complete dynamic recrystallization (DRX) together with some nanoscale and/or sub-microscale Mg2Sn and Mg2Ca precipitates could be obtained after extrusion. The tensile yield strength, ultimate tensile strength and elongation of the extruded dilute alloy were 213 and 266 MPa, and 21%, respectively. The correlation between microstructural characteristics and properties was also discussed.

Effects of Extrusion Processing on Microstructure of 7075Al Alloy in the Semi-solid State

A recrystallization and partial melting (RAP) process was introduced to prepare the semi-solid 7075 aluminum alloy used for thixoforming. In order to obtain an ideal semi-solid microstructure, a series of extrusion experiments were conducted to comparatively investigate the optimum extrusion process parameters. Commercial 7075Al alloy samples were frstly extruded with varying extrusion ratios below the recrystallization temperature followed by homogenization, then these samples were reheated to the semi-solid state and held in the range of 5 to 50 minutes. The experimental results show that varying process cause the difference in the deformation degree and microstructure for as-extruded samples, resulting in various semi-solid microstructure. It is verifed that the formation of equiaxed grains in semi-solid microstructure depends on recrystallization behavior of extruded samples during partial melting. Both relative high extrusion temperature and low extrusion ratio lead to high volume fraction of recrystallized area, thus entirely equiaxed solid grains in semi-solid 7075Al alloy samples can be obtained finally. In addition, Ostwald ripening was determined as the dominate coarsening mechanism of solid grains in semi-solid state for this 7075 Al alloy during the RAP route. The infuence of pre-deformation on recrystallization behavior of this 7075 Al alloy was discussed in detail.

Strength properties and structure of CuCrZr alloy subjected to low-temperature KOBO extrusion and heat treatment

KOBO extrusion of metals and alloys strongly activates the point defect generation processes, as a result of which they reach a concentration exceeding the equilibrium level by many orders of magnitude. This leads to significant acceleration of diffusion phenomena which in heat-treatable alloys may cause disturbance of the thermodynamic equilibrium between the solid solution decomposition and dissolution of precipitates. In this work, measurements of mechanical and electrical properties and structural observations Cu1Cr0.1Zr alloy subjected to low-temperature KOBO extrusion at different stages of multi-variant heat treatment were conducted. In addition, the geometry of the extruded alloy’s flow zone was analyzed and the obtained results made it possible to assess the effectiveness of experimental procedures, including product formation with high extrusion ratio λ, aimed at achieving of high and thermally stable functional properties of the material.

Effect of extrusion ratios on microstructural evolution, textural evolution, and grain boundary character distributions of pure copper tubes during hydrostatic extrusion

This study fabricated Cu tubes by hydrostatic extrusion at various extrusion ratios from 2.7 to 6.5 at ambient temperature and then investigated the effects of the extrusion ratios on the microstructural evolution, textural evolution, and coincidence site lattice (CSL) boundary distribution. The hydrostatic extrusion process affected the grain recovery when the Cu tube was hydrostatically extruded at a certain extrusion ratio, resulting from the decrease in dislocation density calculated by the kernel average misorientation (KAM) values based on EBSD data. The fraction of the low-energy Σ 3 boundaries increased sharply at the highest extrusion ratio, resulting in grain recrystallization, followed by grain growth. The rolling texture components present in microstructure of Cu tubes are a function of the extrusion ratio. This study reports for the first time that the microstructure of Cu tubes can be developed by grain recovery and recrystallization, as well as by increasing the content of the rolling texture components. This is attributed to the heat generated during severe plastic deformation (SPD) at an extrusion ratio of 6.4, and the adiabatic heat plays a key role in dislocations, thus overcoming the obstacles faced during thermal activation and boundary migration under specific conditions of hydrostatic extrusion.

The effect of Ce addition (up to 3%) and extrusion ratio on the microstructure and tensile properties of ZK60 Mg alloy

In this study, attempts have been made to investigate the effects of both Ce addition and Extrusion Ratio (ER) on the microstructure and tensile properties of ZK60 alloy. With this aim, different amounts (1, 2 and 3 wt%) of Ce were added to a based ZK60 alloy and then the investigated alloys experienced the hot extrusion process with different ERs (12:1 and 18:1). It was found out that Ce addition could refine the cast (non-deformed) microstructure as the finest grain size (35 μm) was obtained in Ce-containing (3 wt%) alloy. Besides, the results of XRD demonstrated that, in addition to Mg7Zn3 that already existed in the base alloy, a new precipitate (MgZn2Ce) would form in the presence of Ce. This led to an increase in fraction of the precipitates with Ce addition. Microstructural observations showed that applying the extrusion process on the cast alloys, especially with higher ER, would significantly refine the size of grains and precipitates. The grain refinement might be due to the microstructural evolutions taken place during exerting the extrusion forces as well as the dynamic recrystallization. It was found out that Ce addition in both cast and deformed conditions could enhance the hardness and strength of the alloys, while it would have no or negative effect on their elongation. Compared to the cast condition, extruded alloys exhibited far better mechanical properties, especially when higher ER (18:1) has been employed; as the highest hardness (88 HV), yield (308 MPa) and tensile strengths (354 MPa) have been obtained in 3 wt% Ce-containing alloy extruded with ER of 18:1. However, higher ER resulted in lower elongation of the studied alloys.

Effect of Extrusion Ratio on the Microstructure and Mechanical Properties in an Al-Cu-Mg-Ag Alloy

In order to examine the effect of extrusion ratio on the microstructure and mechanical behavior in Al-Cu-Mg-Ag alloy, the Al-6.3Cu-0.48Mg-0.4Ag alloy was subjected to extruding with different extrusion ratios of 17, 30 and 67. The results indicate that the grains are refined and the strength is improved effectively with increasing extrusion ratio. However, further investigation shows that the extrusion ratio of 30 is more effective than the lower extrusion ratio (17) and the higher extrusion ratio (67) to refine the grains in the T6-temper alloy. Moreover, the sample with an extrusion ratio of 30 obtains more precipitates and superior mechanical properties after T6 treatment. This study supports the idea that there exists a critical extrusion ratio for grain refinement and improvement of mechanical properties for the T6-temper alloy. Recrystallization and precipitation during T6 treatment were introduced to explain the effects of extrusion ratio on the microstructure and mechanical properties of the Al-Cu-Mg-Ag alloys.