Conventional Hot Extrusion Research Articles

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.

A scalable method for preparing Al–Mg–Si–Cu alloy profile with varies heterogeneous structures and their relationship with mechanical properties

This work reports a simple method for manufacturing heterogeneous structured Al–Mg–Si–Cu alloy profile modified by TiB2–TiC particles using conventional hot extrusion and solution heat treatment. The heterogeneous structures containing different proportions of coarse grains and fine grains can be regulated by the solution treatment time, and their relationships with the mechanical properties are studied. The results show that the formation of the heterogeneous structure in the alloy is attributed to the non-uniform distribution of the TiB2–TiC particles, which have strong inhibition effects on the recrystallization in the particle-rich zone. When the proportion of coarse/fine grains in the heterostructure is about 2:1, the mechanical properties of the solution-treated alloy profile achieved a high level: tensile strength and yield strength are 345 MPa and 227 MPa, respectively, which are 35% and 53% higher than those of the as-extruded alloy with almost no loss of elongation. This work provides a strategy to advance the scalable manufacturing of heterogeneous structured Al alloy profile for various applications.

Improving the Mechanical Properties of Mg-5Al-2Ca-1Mn-0.5Zn Alloy through Rotary Swaging.

To meet the demand for more extensive applications of Mg alloys, a Mg-5Al-2Ca-1Mn-0.5Zn alloy without RE was prepared in this paper, and its mechanical properties were further improved by conventional hot extrusion and subsequent rotary swaging. The results show that the hardness of the alloy decreases along the radial central region after rotary swaging. The strength and hardness of the central area are lower, but the ductility is higher. The yield strength and ultimate tensile strength of the alloy in the peripheral area after rotary swaging reach 352 MPa and 386 MPa, respectively, while the elongation remains at 9.6%, exhibiting better strength-ductility synergy. The grain refinement and dislocation increase caused by rotary swaging promoted strength improvement. The activation of non-basal slips during rotary swaging is an important reason for the alloy to maintain good plasticity while improving strength.

The Effect of Sub- and Near-Critical Carbon Dioxide Assisted Manufacturing on Medical Thermoplastic Polyurethane.

Incorporating thermally labile active pharmaceutical ingredients for manufacturing multifunctional polymeric medical devices is restricted due to their tendency to degrade in the hot melt extrusion process. In this study, the potential of sub- and near-critical carbon dioxide (CO2) as a reversible plasticiser was explored by injecting it into a twin-screw hot melt extrusion process of Pellethane thermoplastic polyurethane to decrease its melt process temperature. Its morphological, throughput, thermal, rheological, and mechanical performances were also evaluated. The resultant extrudates were characterised using scanning electron microscopy, parallel plate rotational rheometer, differential scanning calorimetry, thermogravimetric analysis, and tensile testing. The process temperature decreased from 185 to 160 °C. The rheology indicated that the reduction in melt viscosity was from 690 Pa.s to 439 Pa.s (36%) and 414 Pa.s (40%) at 4.14 and 6.89 MPa, respectively. The tensile modulus in the elastomeric region is enhanced from 5.93 MPa, without CO2 to 7.71 MPa with CO2 at both 4.14 and 6.89 MPa. The results indicate that the employment of both sub- and near-critical CO2 as a processing aid is a viable addition to conventional hot melt extrusion and that they offer more opportunities for thermosensitive drugs to be more stable in the molten stream of Pellethane thermoplastic polyurethane.

Bimodal microstructure evolution and strength-ductility co-enhancement of hot-extruded Al–La–Mg–Mn alloy

Novel heat-resistant Al-(La, Ce) alloys are strengthened via alloying with high Mg; however, their ductility deteriorates due to the formation of coarse intermetallics. In this work, a conventional hot extrusion process was used to refine the microstructures of Al–La alloy with a high Mg addition. Bimodal intermetallic and grain structures were observed in the as-extruded alloy. Of note, the coarse intermetallics were decorated with high-density microcracks. The as-extruded alloy achieved a good balance between strength and ductility, exhibiting a high ultimate tensile strength (360 ± 2 MPa) and good elongation (9.6 ± 0.6%). The high strength was mainly attributed to the strong strain-hardening ability and the load-transfer effect. Good elongation arises from the propagation of pre-existing microcracks, microstructure refinement, and increased strain-hardening ability. These findings reveal that a combination of pre-existing microcracks and a matrix with strong strain-hardening ability is a promising feature for microstructural design with increased ductility.

Achieving high strength and high ductility in ZK60 alloy with a heterogeneous lamella structure

Heterogeneous structure emerges as a novel design philosophy for metal materials to break through the strength-ductility tradeoff. Here we present a heterogeneous lamella (HL) structure in ZK60 alloy that was fabricated by conventional powder metallurgy techniques, i.e., powder pretreatment and hot extrusion. The distinctive structure consists of soft coarse-grained (CG) lamella embedded in the hard ultrafine-grained (UFG) matrix. Compared to the homogeneous CG and UFG counterparts, the HL ZK60 alloy exhibits an excellent combination of tensile yield strength (404.4 MPa) and uniform elongation (13.5 %). This strength-ductility synergy can be attributed to the hetero-deformation induced (HDI) strengthening and HDI strain hardening as a result of the deformation incompatibility and mutual constraint between the hetero-zones.

Microstructure, mechanical and tribological properties of (APC+B4C)/Al hybrid composites prepared by hydrothermal carbonized deposition on chips

A hybrid reinforced Al matrix composite (AMC) was prepared by hydrothermal carbonized deposition on chips (HTCDC) and a hot extrusion process. The microstructure, tensile strength, hardness and tribological properties of the (APC+B4C)/Al hybrid composites were investigated. The results reveal that nanosized B4C particulates (nano-B4Cp) can be used as nucleation sites to facilitate nucleation and growth of amorphous carbon (APC) by encapsulating nano-B4Cp. It was found that the strength of APC spheres formed by encapsulating nano-B4Cp is higher than that of the original APC spheres. The dislocation density of the Al matrix increases in the conventional hot extrusion process because of the presence of nano-B4Cp, which promotes recrystallisation nucleation. With increasing nano-B4Cp content, the grain size of the Al matrix decreases from 18.80 µm to 8.62 µm. The strength and hardness of the (APC+B4C)/Al hybrid composites first increase and then decrease. For a nano-B4Cp content of 3%, the (APC+B4C)/Al hybrid composite shows the highest strength and hardness of 95.8 ± 0.7 HV and 235.41 ± 1 MPa, respectively. The main reinforcement mechanisms for AMC were analysed, which include the grain refinement strengthening mechanism, the dislocation strengthening mechanism and the load transfer mechanism. The coefficient of friction (COF) and wear rate of the composites decrease with increasing nano-B4Cp content from 0.41 and 2.87 × 10−5 mm3/(Nm) to 0.296 and 0.82 × 10−5 mm3/(Nm), respectively. The increased wear resistance is attributed to the increase in hardness of the composites and the formation of an APC lubricating film and oxide layer between the wear surfaces.

Microstructural Assessment of a Multiple-Intermetallic-Strengthened Aluminum Alloy Produced from Gas-Atomized Powder by Hot Extrusion and Friction Extrusion.

An aluminum (Al) matrix with various transition metal (TM) additions is an effective alloying approach for developing high-specific-strength materials for use at elevated temperatures. Conventional fabrication processes such as casting or fusion-related methods are not capable of producing Al–TM alloys in bulk form. Solid phase processing techniques, such as extrusion, have been shown to maintain the microstructure of Al–TM alloys. In this study, extrusions are fabricated from gas-atomized aluminum powders (≈100–400 µm) that contain 12.4 wt % TM additives and an Al-based matrix reinforced by various Al–Fe–Cr–Ti intermetallic compounds (IMCs). Two different extrusion techniques, conventional hot extrusion and friction extrusion, are compared using fabricating rods. During extrusion, the strengthening IMC phases were extensively refined as a result of severe plastic deformation. Furthermore, the quasicrystal approximant IMC phase (70.4 wt % Al, 20.4 wt % Fe, 8.7 wt % Cr, 0.6 wt % Ti) observed in the powder precursor is replaced by new IMC phases such as Al3.2Fe and Al45Cr7-type IMCs. The Al3Ti-type IMC phase is partially dissolved into the Al matrix during extrusion. The combination of linear and rotational shear in the friction extrusion process caused severe deformation in the powders, which allowed for a higher extrusion ratio, eliminated linear voids, and resulted in higher ductility while maintaining strength comparable to that resulting from hot extrusion. Results from equilibrium thermodynamic calculations show that the strengthening IMC phases are stable at elevated temperatures (up to ≈ 600 °C), thus enhancing the high-temperature strength of the extrudates.

Controlled Grain Refinement of Biodegradable Zn-Mg Alloy: The Effect of Magnesium Alloying and Multi-Pass Hydrostatic Extrusion Preceded by Hot Extrusion

To satisfy the most stringent criteria in terms of new cardiovascular stents, pure Zn was alloyed with 1 wt pct of Mg and subsequently subjected to plastic deformation, using conventional hot extrusion followed by multi-pass hydrostatic extrusion. A detailed microstructural and textural characterization of the obtained materials was conducted, and mechanical properties were assessed at each pass of deformation process. In contrast to pure Zn, hydrostatically extruded low-alloyed Zn is characterized by a remarkable increase in strength and ductility (YS = 383 MPa, E = 23 pct), exceeding the values needed for stents. Such behavior is associated with a dual microstructure containing fine-grained Zn, alternatively arranged with bands of a fragmented eutectic. Extensive grain refinement was achieved due to the process of continuous dynamic recrystallization. Hydrostatic extrusion changes the initial langle 10bar{1}0rangle fiber texture to a 〈0002〉 and langle 10bar{1}1rangle double fiber texture in which the 〈0002〉 component decreases with each pass of hydrostatic extrusion. The gradual evolution of texture components was simulated using a visco-plastic self-consistent model, which confirmed that, during hydrostatic extrusion, secondary slip systems were activated involving mostly the pyramidal one.

The Fundamental Comparison of Zn-2Mg and Mg-4Y-3RE Alloys as a Perspective Biodegradable Materials.

Biodegradable materials are of interest for temporary medical implants like stents for restoring damaged blood vessels, plates, screws, nails for fixing fractured bones. In the present paper new biodegradable Zn–2Mg alloy prepared by conventional casting and hot extrusion was tested in in vitro and in vivo conditions. Structure characterization and mechanical properties in tension and compression have been evaluated. For in vivo tests, hemispherical implants were placed into a rat cranium. Visual observation of the living animals, an inspection of implant location and computed tomography CT imaging 12 weeks after implantation were performed. Extracted implants were studied using scanning electron microscopy (SEM) on perpendicular cuts through corrosion products. The behaviour of zinc alloy both in in vitro and in vivo conditions was compared with commercially used Mg-based alloy (Mg–4Y–3RE) prepared by conventional casting and hot extrusion. Both compressive and tensile yield strengths of Zn and Mg-based alloys were similar; however, the brittleness of Mg–4Y–3RE was lower. Zn and Mg-based implants have no adverse effects on the behaviour or physical condition of rats. Moreover, gas bubbles and the inflammatory reaction of the living tissue were not detected after the 12-week period.

Predicting weld-quality in direct hot extrusion of aluminium chips

Based on a physically motivated weld strength model by Cooper and Allwood a weld quality model for the prediction of the process success in direct hot extrusion of aluminium chips is presented. The results are validated against a variety of literature results as well as against the results of additional hot extrusion experiments utilizing flat-face dies for the production of round bars and porthole dies for the production of hollow profiles. A procedure is presented to determine the minimum required weld quality value necessary to provide a process success by the example of chips made of the aluminium alloy AA6060. The weld model can be used to save time- and cost-consuming experimental try-outs, which may make the process an alternative to conventional hot extrusion due to its clear environmental benefits in the production of complex profiles.

Extrusion of Al-Si alloy compacts under conventional conditions and in the semi-solid state

.In this research work the results of hot extrusion process of aluminium alloy compacts conducted at the temperature of conventional hot extrusion as well as at the temperature range corresponding to the semi-solid state were presented. Initial material was prepared by uniaxial pressing of Al17Si5Fe3Cu1.1Mg0.6Zr alloy powder. The extrusion process was carried out under isothermal conditions, and the temperature stability was strictly controlled. The changes of extrusion force in relation to punch displacement were recorded during hot deformation to demonstrate the effects associated with the appearance of the liquid phase in the volume of the processed material. After extrusion the samples were cooled in water as well as at room temperature. The influence of temperature of extrusion and the resulting fraction of the liquid phase in the processed material on its microstructure and chosen mechanical properties were determined. Mechanical properties of the examined alloy after deformation were carried out by measuring the hardness and in uniaxial compression tests. Additionally, one of the compacts was remelted and cast, what made possible comparison of the microstructure and chosen properties of the obtained products. In the result of the investigations it has been proved, that extrusion in semi-sold state results in reduction of forces necessary to complete deformation process and leads to obtaining the material with good mechanical properties and fine-grained, favourable microstructure.

Fabrication of high-strength Mg-Y-Sm-Zn-Zr alloy by conventional hot extrusion and aging

A high-strength Mg-7Y-5Sm-0.5Zn-0.3Zr alloy was developed successfully by hot extrusion and subsequent aging treatment. The results showed that the as-solutionized alloy mainly contained α-Mg matrix and 14H LPSO phase distributed at grain boundaries. Lamellar LPSO and γ′ phases were dynamically precipitated during hot extrusion and retained after artificial aging treatment at 200°C. After peak-aged treatment, the alloy exhibited excellent mechanical properties with ultimate tensile strength of 465 MPa, 0.2% proof stress of 413 MPa and elongation to failure of 6.5% at room temperature. The high yield strength was attributed to the combined action of 14H-LPSO phase, basal γ′ precipitates and dense distribution of β′ precipitates at prismatic plane.

Mechanical Properties of Al/BN Nanocomposites Fabricated by Planetary Ball Milling and Conventional Hot Extrusion

In this study, Al matrix nanocomposites containing 1, 2 and 4 wt% nano-boron nitride were fabricated by mechanical milling and hot extrusion. The mechanical properties of all extruded samples were evaluated. Also, the morphology and microstructure of the milled composite powders were characterized using two types of electron microscope. The results showed that a high fraction of the boron nitride nanoparticles dissolved and formed a solid solution in Al matrix during the milling process. Through the process of solid solution formation, the work hardening rate of the composite powders increased. This led to a morphological change in the composite powders and resulted in equiaxed shape. The powder particle size also decreased after the milling process. By increasing boron nitride content within a range of 0–4 wt% in the hot extruded samples, tensile stress increased from 212 to 333 MPa. The hardness of the nanocomposite samples including 1, 2 and 4 wt% boron nitride improved approximately 55, 70 and 90% in comparison with pure Al, respectively.

Effect of tube processing methods on microstructure, mechanical properties and irradiation response of 14YWT nanostructured ferritic alloys

In this research, innovative thermal spray deposition (Process I) and conventional hot extrusion processing (Process II) methods have been used to produce thin walled tubing (∼0.5 mm wall thickness) out of 14YWT, a nanostructured ferritic alloy. The effects of processing methods on the microstructure, mechanical properties and irradiation response have been investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and, micro- and nano-hardness techniques. It has been found that these two processes have a significant effect on the microstructure and mechanical properties of the as-fabricated 14YWT tubes. Even though both processing methods yield the formation of various size Y-Ti-O particles, the conventional hot extrusion method results in a microstructure with smaller, homogenously distributed nano-oxides (NOs, Y-Ti-O particles < 5 nm) with higher density. Therefore, Process II tubes exhibit twice the hardness of Process I tubes. It has also been found that these two tremendously different initial microstructures strongly affect irradiation response in these tubes under extremely high dose ion irradiations up to 1100 peak dpa at 450 °C. The finer, denser and homogenously distributed NOs in the Process II tube result in a reduction in swelling by two orders of magnitude. On the other hand, inhomogeneity of the initial microstructure in the Process I tube leads to large variations in both swelling and irradiation induced hardening. Moreover, hardening mechanisms before and after irradiation were measured and compared with detailed calculations. This study clearly indicates the crucial effect of initial microstructure on radiation response of 14YWT alloys.

Consolidation of AA 7075-2 wt% ZrO2 Composite Powders by Severe Plastic Deformation via ECAP

The powders of the AA 7075-ZrO2 were mixed by mechanical milling, but it was found that the system presents a few disadvantages when processed by conventional sintering and hot extrusion, since intermetallic phases between ZrO2 particles and alloying elements were formed. Equal channel angular pressing (ECAP) processing was proposed as an alternative method to consolidate the composite where there is no intermetallic formation. The analysis of the ECAP process showed that the intermediate temperature (220 °C) produced a higher consolidation level than conventional sintering and hot extrusion (400 and 500 °C, respectively). This fact was supported by relative density analysis. In the case of the sintered and hot-extruded sample, the relative density exhibited a value of 0.95, while ECAP sample showed a value of 0.98. Hardness values show that microstructural refinement obtained during mechanical milling was preserved during ECAP processing even when it was carried out at 220 °C.

Cold extrusion of hot extruded aluminum chips

The direct conversion of aluminum alloy machining chips into finished parts by hot extrusion with subsequent cold extrusion was investigated. While the process of hot extrusion was utilized to break the oxides covering the individual chips and to lead to bonding of the pure metal, the processes of cold forward rod extrusion as well as cold backward can extrusion were used for the production of chip-based finished parts. For the hot extrusion process, a flat face die and a die with integrated equal channel angular pressing (iECAP die) were used in order to investigate the influence of the deformation route on the quality of the chip-based finished parts. The flat-face die is a conventional tool for the fabrication of solid sections, while the iECAP die is an experimental tool that integrates the severe plastic deformation process of equal channel angular pressing into a conventional hot extrusion die. Tensile tests revealed superior mechanical properties of chips extruded through the iECAP die compared to those of chips extruded through the flat-face die. The hot extruded chips were further processed at room temperature by either backward can extrusion to cans with different wall thicknesses or by forward rod extrusion to shafts with different values of extrusion ratio and cone angle. For all fabricated chip-based finished parts, the mechanical properties and the microstructure were analyzed. Backward can extrusion of chip-based extrudates fabricated with the iECAP die resulted in defect-free cans for all investigated wall thicknesses, while the cans obtained from flat-face die processed chips showed cracks within the walls. Shafts without visible internal defects could be produced by forward rod extrusion of previously hot extruded chips, independent of the hot extrusion die design. However, subsequent compression tests revealed a dependency of the mechanical properties of chip-based shafts on the hot extrusion die design.

Effects of Extrusion Parameters by KoBo Method on the Mechanical Properties and Microstructure of Aluminum

Abstract Commercial purity aluminum was extruded by means of KoBo method at varied processing parameters. Received extrudates, with different mechanical and electrical properties and work hardening behavior, were obtained. It was found, that some conditions of KoBo extrusion process such as low initial billet temperature, low extrusion rate and low frequency of oscillating die lead to extremely high strength and high electrical resistivity of the material. The absence of work hardening (up to 40% strain) during subsequent groove rolling is also a specific feature of received materials. It was suggested that mentioned features are related to the development of overbalance concentration of point defects (clusters) generated during the extrusion process. During following cold rolling of the extrudate, mentioned defects annihilate at gliding dislocations and make the dislocation climbing and their rearrangement easier. Therefore, until the exhaustion of this mechanism, the hardening of material during cold rolling is very limited. Following increase of the material strengthening at higher rolling strains point to the return of the material to its typical behavior observed for cold deformed aluminum produced by conventional hot extrusion.

Effect of shaping methods on the mechanical properties of Al-SiC composite

Al-SiC composites were successfully produced with improved mechanical properties. Effect of SiC content, its particles size and shaping method were investigated. Three shaping methods of conventional powder metallurgy (PM), hot press (HP) and hot extrusion (EX) were used. The hardness of the samples was measured by Vickers method. Tensile and compression tests were performed for the characterization of mechanical properties. Microstructure was monitored by optical microscopy. Maximum relative density (RD) was obtained for hot pressed samples. Higher SiC content with smaller particles size had the best effect on the mechanical properties such as yielding point (YP), ultimate tensile strength (UTS) and hardness. Maximum hardness (6.57 GPa) and UTS (212 MPa) were obtained for Al-20%SiC with SiC mesh size of 1000. Maximum YP was obtained for Al-20%SiC in compression test (143.64 MPa) that is larger than it in tensile test (117.96 MPa). Remarkable difference exists between HP and extrusion methods at higher SiC contents. The YP of EX samples are larger than HP samples. Strains at known stress (562 MPa) of EX samples are smaller than HP samples.

Mechanical properties and corrosion resistance of Mg–10Gd–2Y–0.5Zr alloy by hot extrusion solid-state recycling

A solid-recycled Mg–10Gd–2Y–0.5Zr alloy is fabricated by hot deforming of machined chips and conventional hot extrusion. All the recycled specimens exhibit higher yield strength compared with the extruded reference ingots under the same extrusion condition, which is mainly ascribed to fine-grain size, dispersive distribution of oxide and the second phase of recycled specimens. When extruded at 450°C, the ultimate tensile strength and elongation of solid-recycled specimen are higher than reference specimen. As for the corrosion resistance, the corrosion rate of 450°C solid-recycled specimen is slightly higher than reference specimen extruded at the same condition. The 400 and 450°C recycled specimens are corroded uniformly, which is better than the pitting of reference specimens. In 450°C recycled specimen, the dispersive distribution of oxide induces that the corrosion products could hinder the progress of corrosion effectively. Meanwhile, the second phase precipitates easily concentrate along the grain boundary in the reference specimens. The aggregates of precipitates induce the appearance of pitting and deep etch pits.