Higher Extrusion Ratio Research Articles

Processing and Characterization of Poly(Lactic Acid) Screw

Usage of the conventional bioabsorbable plastic bone fixation devices have been limited, because the mechanical characteristics of them are lower. In this study, poly-L-lactide ( PLA ) which is one of the bioabsorbable plastic was molded into the screw shape and the mechanical characteristics of the PLA screw was investigated. In order to strengthen by orientation of molecular chain, a PLA screw was prepared by extruding a rectangular PLA block followed by forging. The molding conditions were varied to evaluate the formability of PLA. The mechanical properties, such as pulled out strength, shearing strength and the twist strength were measured. The cross-sectional surface of the thread was observed and the crystallinity was measured. Decrease in void in the thread for the screw extruded using lubricants were observed. This results suggested void formation in the thread was caused at higher extrusion ratio. Decrease in shear strength and increase in twist strength were observed for the screw extruded using lubricants, which is due to lower extrusion ratio. Same tendency is observed for the screws molded at higher temperature. These results suggested the lubrication and higher molding temperature have similar effects. Decrease in twist strength at molding temperature of 120°C was obtained, which was caused by embrittlement due to crystallization.

Effects of Hot Extrusion Processes on Grain Size of ZK60 Alloy Tubes

Effects of hot extrusion processes on grain size of ZK60 alloy tubes was researched by combining numerical simulation with experimental research. The results show that grain size varies inversely as extrusion ratio and extrusion speed, with extrusion temperature being constant. In order to get the finer and homogeneous microstructure, higher extrusion ratio, higher extrusion speed and lower billet temperature should be chosen in the equipment's rated load. Isothermal extrusion is conducive to tube forming , and the smallest grain size and the better microstructure can be obtained at temperature of 300°C when other deformation conditions are constant.

Microstructural refinement and mechanical properties of direct extruded ZM21 magnesium alloys

Cast ZM21 magnesium alloys were subjected to symmetric extrusion at four different temperatures (200, 250, 300 and 350 °C) with three extrusion ratios of 4:1, 9:1 and 16:1, respectively. The effects of extrusion parameters such as temperature and extrusion ratio were studied by optical microscopy, X-ray diffraction (XRD) and tensile test. The optical micrographs exhibited various stages of recrystallization, i.e., partial to full recrystallization influencing mechanical properties to good extent. Higher extrusion temperature resulted in coarse grains, whereas finer grains were obtained at higher extrusion ratios. Ultimate tensile strength of this alloy was increased from 160 MPa to 316 MPa after extrusion at 250 °C with an extrusion ratio of 9:1.

A Comprehensive Model for Predicting Profile Exit Temperature of Industrially Extruded 6063 Aluminum Alloy

The effects of extrusion parameters on the resulting profile exit temperature of industrially extruded 6063 aluminum alloy have been studied using statistical design of experiments (DOE). Two operating parameters (initial billet temperature and ram speed) and three geometrical parameters (extrusion ratio, profile average thickness, and number of die cavities) were investigated. A statistical model was obtained for predicting profile exit temperature with very close agreement between predicted and measured values. Present results indicated that the main contribution towards profile exit temperature comes from plastic work promoted by high extrusion ratios, high initial billet temperatures, and high ram speeds. Further contributions are promoted by parameters affecting friction and redundant work components. In addition to single-factor effects, profile exit temperature was revealed to be affected by a set of complex two-factor and three-factor interactions between the different operating and geometrical parameters. The most remarkable two-factor interactions were shown to exist between extrusion ratio and number of die cavities and between initial billet temperature and ram speed. Complex three-factor interactions have been shown to exist between extrusion ratio, initial billet temperature, and ram speed. These interaction effects are quantified in the present model and are further qualitatively discussed in terms of their effects on the resulting profile exit temperature.

The role of Zr-rich cores in strength differential effect in an extruded Mg–Zn–Zr alloy

This work examines the effects of extrusion parameters namely ratio and temperature on recrystallization behavior of a Mg–Zn–Zr alloy, and their consequent effects on anisotropy in the mechanical properties. Upon extrusion, the characteristic Zr-rich cores that do not recrystallize form the so-called “soft stringers” which are deformed bands elongated in the extrusion direction and curled around the extrusion axis. At higher extrusion ratio, there is more twinning contribution and the DRX response is improved, making the recryatallized grains finer and increasing the proportion of recrystallized Zr-rich cores. A basal texture after extrusion and the directional activation of tensile twinning cause anisotropy in the mechanical properties. In addition, the microstructural features such as large unrecrystallized regions and coarse crystallized grains also contribute in the strength differential effect. Further slip in the strain-hardened unrecrystallized grains is inhibited while twin activation under favorable orientation becomes easier in the coarse recrystallized grains. A higher proportion of large unrecrystallized and coarse crystallized gains in the case of lower extrusion ratio result in a much higher strength differential effect (∼100 MPa) in comparison to the one caused by the crystallographic texture only (∼25 MPa).

Effect of Al-6063 Billet Quality on the Service Life of Hot Extrusion Die: Metallurgical and Statistical Investigation

The current paper presents results about the effect of Al-6063 billet quality on the service life of AISI-H13 hot extrusion dies based on microstructural and statistical investigation. In the first half of the paper, secondary (remelt) billet cast in-house at local extrusion plant is compared with two sources of primary (smelter) billet by applying different material characterization techniques including optical microscopy, hardness measurement, x-ray diffraction (XRD) analysis, and energy-dispersive spectroscopy (EDS). The second half of the paper evaluates the performance of primary and secondary billet types based on statistical analysis of data collected on 53 hollow-profile dies from a local commercial extrusion setup. It was observed that the secondary billet has a comparatively coarse grain structure, nonhomogeneous distribution of secondary phases, and high hardness that can be associated with poor casting and homogenization practice. Statistical analysis covers overall analysis of collected data followed by detailed study of percentagewise use of billet quality in terms of die profile complexity/extrusion ratio. Analysis has shown that dies extruding a high percentage of secondary billets are more susceptible to early die failure on overall basis. For more complex dies with high extrusion ratio, average die life further reduces with increased percentage of secondary billet usage. Regression models are also proposed for prediction of die life in terms of secondary billet usage and extrusion ratio. Considering results of present microstructural and statistical analysis, some suggestions during in-house billet preparation of secondary billets have been formulated to prevent early die failure.

Comparison of Microstructure and Mechanical Properties between ZM21 and ZME210 with Different Hot Extrusion Ratios

The mechanical properties and microstructure of the as-extruded ZM21 magnesium alloy and its modified alloy ZME210 with addition of 0.35wt% cerium were investigated with different extrusion ratios from 14 to 182 by using mechanical property test, microscopic structure quantitative analysis, SEM observation and energy spectrum analysis. The results showed that both ZM21 and ZME210 had an extrusion ratio limit for grain refining, and the grains were found to be finer with higher extrusion ratio when the ratio was not higher than the limit value. The extrusion ratio limit for the best effect for grain refining of ZME210 is lower than that of ZM21. It was found that the Ce can refine the grains effectively after hot extrusion with different extrusion ratios. The effects of Ce on the microstructure and mechanical properties were analyzed.

Structure and properties of 6061 + 26 mass% Si aluminum alloy produced via coupled rapid solidification and KOBO-extrusion of powder

Experiments on mechanical consolidation of rapidly solidified (RS) powder of 6061 + 26 mass% Si alloy were performed using the oscillating-die extrusion method. The RS powder was wrapped in thin-wall 6061-alloy cup 35 mm in diameter and vacuum-compressed by means of 100 ton press. Bars 8 mm in diameter were extruded with cross-section reduction of λ = 19 without any preheating of the charge. Tubes with a diameter/wall thickness of 14 mm/1 mm and cross-section reduction of λ = 33 were also manufactured with success. TEM/STEM observations revealed a very fine structure of as-extruded material and bimodal distribution of quasi-spherical silicon particles. Statistical analysis revealed a silicon fine fraction of 0.1–0.7 μm and a coarse fraction 2.1–2.5 μm in diameter. Examination by means of TEM did not reveal any significant changes in the morphology of the silicon particles, even when a high extrusion ratio and the material annealing after deformation were used. Hot compression tests on as-extruded rods ( λ = 19) and preliminary annealed samples were performed at a constant true strain rate of 5 × 10 −3 s −1 within the temperature range of 293–823 K. High strength of the material and relatively high ductility of samples deformed by compression up to ɛ t ≅ 0.4 were observed. The maximum flow stress value for as-extruded material was reduced with deformation temperature from ∼390 to ∼3.5 MPa for 293 and 823 K, respectively. Annealing of the samples at 773 K/30 min was found to reduce the maximum flow stress by 30–40%. Tensile strengths of similar as-cast alloys and materials manufactured by means of other powder metallurgy methods were shown for the purpose of comparison.

A study on reheating characteristics for thixo die casting process with electromagnetic stirring and extruded aluminum alloys and their mechanical properties

In this paper, the reheating process and mechanical properties of thixo die cast A356 alloy, using electromagnetic stirring (EMS) and extrusion before thixo die casting, were discussed. The EMS is used mainly to manufacture raw materials with a globular microstructure. If relevant reheating is carried out, products with excellent mechanical properties can be manufactured by EMS. Contrarily, extruded material has a fine dendrite microstructure and has rarely been assumed to be suitable for the thixo die casting process. This study demonstrated that the microstructure of extruded material could be globularized and applied to the thixo die casting process only with the relevant reheating parameters. This applicability was estimated through image analysis obtaining the solid fraction, the mean equivalent diameter, and roundness under various reheating conditions. After thixo die casting experiments using three materials, which were EMS, low-extrusion material (LER), and high-extrusion ratio materials (HER), mechanical properties were comparatively analyzed. EMS and HER materials show better mechanical properties than LER.

Superplasticity in Mg–Li–Zn Alloys Processed by High Ratio Extrusion

Superplastic behavior of Mg-8.5Li-1Zn and Mg-8.5Li-3Zn alloys has been investigated. Dynamic recrystallization occurs in the Mg–Li–Zn alloys during extruding with high ratio after stir casting. Mg-8.5Li-1Zn alloy exhibits an elongation of about 400% at the high strain rate of 1.1 × 10−2 S−1 at 623 K, while the Mg-8.5Li-3Zn alloy shows maximum elongation of more than 540%. The apparent activation energy for superplastic flow of both Mg-8.5Li-1Zn and Mg-8.5Li-3Zn alloys at 573–673 K is about 86 kJ/mol and 79 kJ/mol, respectively, so that the dominant deformation mechanism in Mg–Li–Zn alloys is grain boundary sliding (GBS) controlled by grain boundary diffusion.

Application of fuzzy theory to predict deformation behaviors of magnesium alloy sheets under hot extrusion

Abstract The study predicts forming behaviors and tensile strength of the magnesium alloy sheet under extrusion in converging dies using fuzzy theory. The variable speed method was used to extrude perfect magnesium alloy sheets with a high extrusion ratio. However, the selection of adjustment timing would affects the success of sheet forming. Therefore, if fuzzy theory can be applied to predict the adjustment timing, then the experimental effectiveness of the trial and error method for adjustment timing will definitely increase. The billets used in this study were AZ31 and AZ61 magnesium alloys, and the two corresponding sets of converging dies had semi-die angles of 20° and 40°, respectively. The process parameters are set using orthogonal arrays (OA), which are used in the experiments. The experimental results are then used to establish the predictive model based on fuzzy theory. The variable speed timing and the tensile strength of the final product are then predicted at semi-die angles of 20°, 30° and 40°, and at heating temperatures of the billet between 320 °C and 360 °C. Further experiments are performed to verify the accuracy of the approach.

An investigation of cold extruding hollow flanged parts from sheet metals

Hole flanging with cold extrusion can avoid necking or fracture as encountered in conventional sheet metal-forming operations. Substantial flange height and lip thickness can be achieved with flange extrusion because the forming load is compressive. Using a hydraulic press, flange extrusions of 5 and 10 mm inner diameters were produced in pieces of cup-shaped galvanized steel, as well as aluminum 5052 workpieces with a thickness of 0.8 mm, both of which had a pre-hole on the cup bottom. As the punch load was exerted on the cup rim, a clamping force was applied to suppress dilation on the cup bottom. The experiments showed that with sufficient clamping force, significant flange height could be extruded. The utmost extruded flange of 5 mm i.d. was 6 times larger than that drawn from the conventional method, whereas that of 10 mm i.d. was 3.8 times larger than that drawn from the conventional method. However, no flange was extruded and buckling occurred on the cup bottom when the clamping force was insufficient. The experiments confirmed the results predicted by the FE simulation. For a selected flange inner diameter, the ratio of the extruded flange height to the increase in cup bottom thickness was directly related to the normalized clamping pressure, i.e. the ratio of clamping pressure to workpiece yield strength. Therefore, both the application of a larger clamping force or the use of low-strength workpiece materials facilitated the extrusion of flange while suppressing the dilation of the cup bottom. Flange extrusions with a larger diameter correspond to a smaller extrusion ratio or reduction of area. Experiments showed that a significant flange height could be extruded with a 10 mm inner diameter for both galvanized-steel and aluminum 5052, while results for extrusions with a 5 mm inner diameter were unfavorable when using galvanized-steel. High-strength materials and a high extrusion ratio required greater clamping force for the flange extrusion process, and consequently caused excessive forming load on the forming dies as well as on the hydraulic press, thus rendering the process less effective.

Superplasticity evaluation in an extruded Mg–8.5Li alloy

With the remarkable feature of a combination of ultra lightness and improved formability at room temperature, magnesium–lithium (Mg–Li) base alloys are deserving increased attention among the high-performance Mg alloys for either academic or technical interest [1, 2]. It has been reported that Mg–Li base alloys in the eutectic composition range, with their microstructure consisting of two phases of hexagonal a (Mg-rich phase) and centered cubic b (Li-rich phase), can produce superplasticity under appropriate thermo-mechanical processing and testing conditions [3–7]. But to date, only few of them were found to show large elongation at high strain rates more than 10 s –1 [8]. Similar to aluminum alloys and other metal-based materials, developing high strain rate superplasticity in magnesium alloys would be of benefit for their commercial forming applications [9]. An attempt to obtain superplasticity in a Mg–8.5Li alloy prepared by stir casting and high ratio extrusion has been made in this work and the results will be introduced herewith. The composition of the studied binary Mg–Li alloy was selected as Mg–8.5Li (wt. %) which is within the typical eutectic range and has been proved to make a (a + b) twophase mixture microstructure [10, 11]. The alloy was cast by a stirring route followed by high ratio (100:1) extrusion at 623 K. Round tension specimens with a 2.5 mm diameter and a 15 mm gage length were directly made from the extruded rods of 4 mm in diameter. Tension test specimens were deformed at initial strain rates ranging from 9 · 10 to 9 · 10 sand at 573 K, 623 K and 673 K, respectively. Microstructure of the specimens before and after deformation was examined by optical microscopy. Superplastic characteristics of the Mg–8.5Li alloy at the examined temperatures are shown in Fig. 1. As seen from Fig. 1 (a), the flow stress of the Mg–8.5Li alloy increases as the strain rate increases or as the testing temperature decreases. The strain rate sensitivity exponent, m value, is about 0.40 at 623 ~ 673 K at strain rates ranging from 10 to 10 s, and decreases to 0.20 at the strain rate higher than 10 s .The variation of total elongation in the Mg–8.5Li alloy with strain rate is illustrated at Fig. 1 (b). At the same strain rate, the Mg–8.5Li alloy exhibits higher an elongation value at 623 K that at 573 K and 673 K. A maximum elongation of more than 500% is obtained at the strain rate of 1 · 10 s at 623 K, indicating that the studied Mg–8.5Li alloy has the potential to produce superplasticity at higher strain rate. Typical deformed specimens along with the tension specimen before test are shown in Fig. 2. The superplastic behaviors reported to date in the Mg–Li based alloys depend much on the fabrication and processing history and the resulting microstructure of the alloys, and almost all involve a rolling process [3–6]. The Mg-8.5– 9%Li laminates prepared by a foil metallurgy route exhibited a larger elongation of 450% ~ 460% at initial S. L. Dong School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China

Superior Corrosion Resistance and Mechanical Properties of a Mg Alloy Recycled by Solid-State Process

Superior mechanical properties of the recycled specimen by solid-state recycling were introduced at first. AZ31 Mg machined chips were recycled by extrusion at 673 K with the different extrusion ratios. The oxide contaminants were dispersed more uniformly in the recycled specimen with the high extrusion ratio (1600:1). There was a remarkable increase in tensile strength and 0.2% yield stress for the recycled specimen with the high extrusion ratio compared with an extrusion reference subjected to the same deformation history. Next, superior corrosion resistance of the recycled specimen was introduced. The recycled specimen with low extrusion ratio (45:1) possessed superior corrosion resistance compared with the extrusion reference. The enhancement of corrosion resistance for the recycled specimens was attributed to the presence of oxide contaminants which were distributed parallel to the extrusion direction.

Effects of extrusion ratio on the microstructure and mechanical properties of AZ31 Mg alloy

Experiments were conducted to evaluate the effects of extrusion ratio on grain refinement and subsequent mechanical properties at room temperature of AZ31 Mg alloy by backward extrusion. The backward extrusion was undertaken with extrusion ratio of 7, 24, 39, 70 and 100 at 250 °C. The results indicate with increasing extrusion ratio the grain of AZ31 Mg alloy is refined and the mechanical properties at room temperature are improved effectively. Further investigation shows that higher extrusion ratio (≥39) is more effective than lower extrusion ratio (≤24) to refine the grains. However, the efficiency of mechanical properties improvement at room temperature for high extrusion ratio is lower than that of low extrusion ratio. This study supports the idea that there exists a critical extrusion ratio for grain refinement and improvement of mechanical properties on certain conditions. Dynamic recrystallization and texture during extrusion are introduced to explain the effects of extrusion ratio on the microstructure and mechanical properties of AZ31 Mg alloy.

Effect of extrusion conditions on grain refinement and fatigue behaviour in magnesium alloys

This paper describes the grain refinement due to controlled extrusion and the fatigue behaviour of the extruded materials in three magnesium alloys, AZ31B, AZ61A and AZ80. First, in order to investigate the effect of working temperature, billets of AZ31B and AZ61A were extruded at an extrusion ratio of 67 under controlled conditions with three different working temperatures. It was found that grain refinement was attained in both alloys whose grain size decreased with decreasing working temperature. Rotary bending fatigue tests were performed using smooth specimens. In AZ31B, fatigue strength increased with decreasing grain size, but in AZ61A, it did not depend on grain size. Fatigue crack initiation and subsequent small crack growth were examined in AZ31B. Consequently, grain refinement improved both crack initiation resistance and small crack growth resistance, resulting in the increase in fatigue strength. Furthermore, it was indicated that fatigue strength was expressed properly by the Hall–Petch relationship in AZ31B, but not in AZ61A. Then, in order to investigate the effect of extrusion ratio, billets of AZ61A and AZ80 were extruded at three different extrusion ratios under controlled conditions. It was found that grain size decreased with increasing extrusion ratio in both alloys, but mechanical properties were not affected significantly by extrusion ratio, i.e. grain size, and the grain size dependence of fatigue strength was different between alloys. In AZ61A, fatigue strength was higher in the material extruded at lower extrusion ratio (coarser grain), but in AZ80, in the material extruded at higher extrusion ratio (finer grain). Fatigue crack initiation behaviour was consistent with the tendency of fatigue strength, where crack initiation delayed in the material extruded at lower extrusion ratio in AZ61A and in the material at higher extrusion ratio in AZ80. Furthermore, the observed grain size dependence of fatigue strength in both alloys was discussed on the basis of a texture formed by extrusion and the presence of inclusions from which cracks generated.

Mechanical properties of AZ31 Mg alloy recycled by severe deformation

AZ31 Mg machined chips were recycled by extrusion at 673 K with a low extrusion ratio of 45:1 and a high extrusion ratio of 1600:1. Oxide contaminants were dispersed more uniformly in the recycled specimen with the high extrusion ratio than in that with the low extrusion ratio. In tensile tests, the recycled specimens with the high extrusion ratio showed about 50% higher 0.2% yield stress and about 20% higher tensile strength compared with those of the reference specimens, which were the extruded AZ31 Mg blocks under the same conditions as the recycled specimens. The improvement of the tensile properties was attributed not only to the small grain size, but also to the dispersed oxide contaminants.

Improving the Mechanical Properties of AZ31 Mg Alloy by High Ratio Extrusion

Experiments were conducted both to evaluate the potential for grain refinement, the subsequent mechanical properties at room temperature in samples of AZ31 Mg alloy and also to investigate the relationship between one-step and two-step high ratio extrusion (HRE). The one-step HRE was undertaken using a high extrusion ratio of 70:1 at 250, 300 and 350°C. And the two-step HRE was conducted with an extrusion ratio of 7 for the first step at 250, 300 and 350°C, followed by a second-step extrusion with an extrusion ratio of 10 at 250, 300 and 350°C. The initial grain size in the AZ31 ingot was 100μm and that after one-step HRE became similar to 5μm, after two-step HRE at 250, 300 and 350°C were 2, 4, 7μm, respectively, resulting in superior mechanical properties at ambient temperature. The microstructure of two-step HRE was finer and uniformer than that of one-step HRE and the strength of one-step and two-step HRE were similar, moreover, the elongation of one-step HRE was improved markedly than that of two-step HRE. Dynamic recrystallization and adjacent grain broking during HRE is introduced to explain the effects of one-step and two-step HRE on the microstructure and mechanical properties of AZ31 Mg alloy. The current results imply that the simple HRE method might be a feasible processing method for industry applications, and the multiply steps extrusion are effective to fabricate high strength of fine grained hcp metals.

Hydrostatic Extrusion of Poly(L‐Lactide)

AbstractPoly‐L‐Lactide(PLLA) has been used as a bone fracture fixation material for several years. However, its mechanical properties are still not satisfied. To improve its mechanical properties, we examined the hydrostatic extrusion procedure on the PLLA rods made by Injection Molding process. The extrusion ratio was adjusted to 3, 6, 9, and 12. The molecular weight of the PLLA decreased from 260,000 to 200,000 after injection molding process, but it did not change during the hydrostatic extrusion procedure. The melting point of PLLA hydrostatic extrusion products were increased with the extrusion ratio, but the increment was not obviouse. Extrusion products having low extrusion ratio had α‐form crystal in them, extrusion products having high extrusion ratio had both of α and β‐form crystall in them. At extrusion temperature of 145°C, PLLA rods showed the best flowing trends in the pressure medium of PEG 400. Extrusion temperature is placed in the range of crystalline transition temperature and melting point of PLLA. At extrusion ratio 9∼12, the extrusion products showed the best mechanical properties. The highest bending strength of the extrusion product was over than 350MPa. It is far stronger than that of the human cortical bone (200MPa). SEM observations showed that the fiber structure began to appear at an extrusion ratio ER=3, and at the extrusion ratio ER=6, the chain axes of PLLA became aligned to the extrusion direction. The structure of extrusion products at the high extrusion ratio showed highly oriented fiber structure composed of micro‐fibril. At high extrusion ratio tranformation from α‐crystal to β‐crystal was also observed.

Application of ANN to the hot extrusion of magnesium alloy sheets

During the hot extrusion of magnesium alloy, its structure is hexagonal close-packed, which has fewer slide surfaces than aluminium alloy. Experiments show that if the hot extrusion of magnesium alloy sheets is performed under a die that has a high extrusion ratio of 35.9, and a fixed speed is adopted, all of the final products carry defects. Restated, sound sheets with zero-defects cannot be obtained. Further experiments were performed on the extrusion of magnesium alloy sheets by the multi-speed method (MSM), and sound sheets were obtained. However, when the multi-speed method of extruding was used, adjusting the initial speed at the appropriate time directly affected the results of experiments. This paper addresses an experiment designed by the method of orthogonal array (OA), and uses magnesium alloy AZ31 and AZ61 as outer OAs, whereas the factors selected as inner OAs are the temperature of the container, the temperature of the material, the initial speed of extrusion, the final speed and the lubricant. Moreover, the OA of L18 is selected to conduct experiments repeatedly and then apply artificial neural networks (ANN) to learn the results of the experiment. To forecast the temperature of the material for an experiment between 340 and 390 °C, curves of the timing of an adjustment of the initial speed of extrusion by the multi-speed method with increments of 5 °C should be plotted. Experiments are performed to confirm the accuracy of ANN analysis.