As-extruded State Research Articles

Effects of Sn on microstructure of as-cast and as-extruded Mg–9Li alloys

The effects of Sn addition on the microstructure of as-cast and as-extruded Mg–9Li alloys were investigated. The results show that α-Mg, β-Li, Li2MgSn, and Mg2Sn are primary phases in the microstructures of the as-cast and as-extruded Mg–9Li–xSn (x=0, 5; in mass fraction, %) alloys. Li2MgSn phase evolves from continuously net-like structure in the as-cast state to fine granular in the as-extruded state. After the extrusion, Mg–9Li–5Sn alloy has finer microstructures. Li2MgSn or Mg2Sn compound can act as the heterogeneous nucleation sites for dynamic recrystallization during the extrusion due to the crystallography matching relationship. Extrusion deformation leads to dynamic recrystallization, which results in the grain refinement and uniform distribution. The as-extruded Mg–9Li–5Sn alloy possesses the lowest grain size of 45.9 μm.

Microstructure, mechanical properties, in vitro degradation and cytotoxicity evaluations of Mg–1.5Y–1.2Zn–0.44Zr alloys for biodegradable metallic implants

Mg–1.5Y–1.2Zn–0.44Zr alloys were newly developed as degradable metallic biomaterials. A comprehensive investigation of the microstructure, mechanical properties, in vitro degradation assessments and in vitro cytotoxicity evaluations of the as-cast state, as-heat treated state and as-extruded state alloys was done. The microstructure observations show that the Mg–1.5Y–1.2Zn–0.44Zr alloys are mainly composed of the matrix α-Mg phases and the Mg12ZnY secondary phases (LPS structure). The hot extrusion method significantly refined the grains and eliminated the defects of both as-cast and heat treated alloys and thereby contributed to the better mechanical properties and biodegradation resistance. The values of tensile strength and tensile yield strength of the alloy in the as-extruded condition are about 236 and 178MPa respectively, with an excellent elongation of 28%. Meanwhile, the value of compressive strength is about 471MPa and the value of bending strength is about 501MPa. The superior bending strength further demonstrates the excellent ductility of the hot extruded alloys. The results of immersion tests and electrochemical measurements in the SBF indicate that a protective film precipitated on the alloy's surface with the extension of degradation. The protective film contains Mg(OH)2 and hydroxyapatite (HA) which can reinforce osteoblast activity and promote good biocompatibility. No significant cytotoxicity towards L-929 cells was detected and the immersion extracts of alloy samples could enhance the cell proliferation with time in the cytotoxicity evaluations, implying that the Mg–1.5Y–1.2Zn–0.44Zr alloys have the potential to be used for biomedical applications.

Effect of Cold Deformation on Microstructure and Mechanical Properties of Mg-8Gd-3Y-0.5Zr Alloy

Pre-cold rolling with the reduction of 15% was employed on Mg-8Gd-3Y-0.5Zr (wt.%) (GW83K) alloy in different initial states: as-extruded (state 1) and extruded followed by annealing (state 2) with the aim to investigate the effects on microstructure and mechanical properties. Microstructure observation revealed that there are more amounts of mechanical twins in the alloy in state 2 than that of the alloy in state 1 after cold rolling, which indicates the different deformation mechanisms. Further investigation through EBSD has elucidated the grain boundary structure and types of twins in the alloys. Pre-cold deformation greatly promotes the age hardening response and the peak aging time at 200°C was found to be nearly 12h for the alloy in both state 1 and state 2, which were about 24h and 80h less than that of their non-deformed counterparts, respectively. Tensile tests at temperatures lower than 250°C showed that the alloy in state 1 has a predominant mechanical property than that of the alloy in state 2, while at 300°C, it displayed a reverse tendency.

In vitro degradation performance and biological response of a Mg–Zn–Zr alloy

Abstract The feasibility of a Mg–Zn–Zr alloy for biomedical applications was studied through microstructure characterization, corrosion tests in different biological media, and cell proliferation, differentiation and adhesion tests. Corrosion tests showed that the ZK60 alloy in the as-extruded state with finer grain sizes exhibited slower corrosion rates than the same alloy in the as-cast state. The tests in different biological fluids showed that the corrosion rates of the as-cast and as-extruded ZK60 alloy in DMEM + FBS were the highest, while those in Hank's solution were the lowest. The corrosion rate of the as-extruded ZK60 alloy was similar to the corrosion rates of other commercial magnesium alloys, namely the die-cast AZ91D, die-cast AM50, extruded AZ31 and extruded WE43 alloys. The results obtained from the indirect cytotoxicity evaluation showed that the 100% concentrated cast and extruded ZK60 alloy extracts resulted in significantly reduced cell numbers and total protein amounts, as compared to the negative control. The cell number and total protein amount increased with the gradual dilution of the extracts, but the protein normalized ALP activity showed an opposite trend. For the direct assay, L-929 and MG63 cells exhibited good adhesion with spread pseudopod on the surface of extruded ZK60 alloy samples after 24 h culture. In short, the as-extruded ZK60 alloy could be a good candidate material for biodegradable implants.

Influence of Thermal and Thermo-Mechanical Processing on the Creep Resistance of Mg-10Gd-3Y-0,4Zr Alloy

Alloy Mg-10Gd-3Y-0,4Zr in as-cast, as-extruded, cast-T6 (peak aged) and extruded-T5 (peak aged) state was tensile creep tested at 200, 250 and 300 °C and stress 50, 80 and 120 MPa. Comparison of minimal creep rate shows that alloy Mg-10Gd-3Y-0,4Zr in cast-T6 conditions is characterized by an excellent creep resistance, which is higher than that of commercially available Mg-alloys. Creep resistance of as-cast, as-extruded and extruded-T5 alloy Mg-10Gd-3Y-0,4Zr is lower. Cavity nucleation is heavily affected by the amount of secondary phases on the grain boundaries and also by the initial grain size of the microstructure. After extrusion and in the extruded-T5 conditions creep cavitation was not observed, whereas in the as-cast and cast-T6 conditions creep cavitation occurred on the high fraction of grain boundaries.

High-strength magnesium alloys for degradable implant applications

This article describes the design principles deployed in developing high-strength and ductile Mg–Zn–Zr–Ca–Mn(–Yb) alloys based on a concept, which aims to restrict grain growth considerably during alloy casting and forming. The efficiency of the development approach is discussed. Moreover, the microstructure and phase analysis of the alloys subjected to different thermal treatments are presented and the influence of the alloy composition, particularly the addition of Yb, on the evolution of the microstructure is discussed in connection with the mechanical properties of the materials. The newly developed alloys exhibit high strength (yield stress of up to 350MPa) at considerable ductility (elongation to fracture of up to 19%) in the as-extruded state and reveal age hardening potential (increase in hardness of 10–15% compared to that in the recrystallization heat-treated state). Appropriate heat treatments enable tailoring of the strength–ductility relation. Thermal annealing of the material resulted in a remarkable increase in ductility (elongation to fracture of more than 20% for all heat-treated samples) while high strength is retained (yield stress ranging from 210 to 315MPa). We attribute the attractive mechanical properties of the developed alloys to their fine-grained microstructure, where the grain boundaries and lattice defects are stabilized by second phase particles formed during casting and thermal treatments.

Influence of impurities on microstructure and mechanical properties of ZK60 magnesium alloy

The influence of impurity content on the microstructure and mechanical properties of ZK60 magnesium alloys was investigated by optical microscopy, scanning electron microscopy and tensile test. ZK60 alloys were prepared by changing holding time of alloy melt during semi-continuous casting in order to control the content of impurity elements. The alloy with lower purity content is found to have less second precipitates and larger grain size in the as-cast state. However, in the as-extruded state, reducing impurities brings about a decrease in grain size and an increase in yield strength from 244 MPa to 268 MPa, while the elongations in the as-extruded alloys with different contents of impurities are almost the same. After T5 treatment, impurity content is found to have more obvious effect on the yield strength of ZK60 alloy. The yield strength of ZK60-45 alloys with low impurity content is increased up to 295 MPa after T5 treatment.

Influence of impurities on damping properties of ZK60 magnesium alloy

The influence of impurities on damping capacities of ZK60 magnesium alloys in the as-cast, as-extruded and T4-treated states was investigated by dynamically mechanical analyzer at room temperature. Granato and Lucke dislocation pinning model was employed to explain damping properties of the alloys. It is found that reducing impurity content can decrease the amount of second-phase particles, increase grain size and improve damping capacity of the as-cast alloy slightly. The as-extruded alloy with lower impurity content is found to possess obviously higher damping capacity in the relatively high strain region than that with higher impurity concentration, which appears to originate mainly from different dislocation characteristics. The variation tendency of damping property with change of impurity content after solution-treatment is also similar to that in the as-extruded and as-cast states. Meanwhile, the purification of the alloy results in an evident improvement in tensile yield strength in the as-extruded state.

DC Casting - Simulation and Microstructure of Mg-Zn Alloys

The market share of wrought Magnesium products such as structural and functional components is recently increasing. Extrusion at elevated temperatures is used to produce reliable plastic deformation, since magnesium alloys have limited ductility at room temperature. In order to produce sound extruded products, high quality billets are required. Understanding the influence of direct chill casting conditions on the production properties such as quality, safety, workability and microstructure have a profound importance. Comprehensive computer simulations were used in order to model the casting so that process parameters can be identified and controlled, resulting in significant benefits. The aim of modeling is to provide temperature profiles for a more accurate solidification analysis, predict the solidification time and the effect of cooling on the solidification. The experimental study included castings of several Magnesium alloys, each with 7 (seven) thermocouples that were submerged into the billet. Verification of the simulations was carried out based on the data collected. Complimentary work was conducted on microstructure analysis in as cast and as-extruded states.

Effect of Zr addition on the mechanical properties of as-extruded Mg–Zn–Ca–Zr alloys

Extrudable Mg–6Zn–0.2Ca(–0.8Zr) alloy (mass%) has been developed. The Mg–Zn–Ca–Zr alloy shows excellent mechanical properties in the as-extruded state with the ultimate tensile strength of 357 MPa and elongation to failure of 18%. These properties are related to dynamic recrystallization, texture and precipitation. Dynamically recrystallized grains are pinned by fine precipitates, resulting in very fine grain size. The extruded sample also exhibits a higher average {0 0 0 2} 〈 1 1 2 ¯ 0 〉 Schmid factor due to the presence of unrecrystallized regions, leading to texture strengthening. Zr may work as a microalloying element, resulting in fine and dense distribution of a MgZn 2 based phase involving Ca and Zr.

Optimization of heat treatment in cold-drawn 6063 aluminium tubes

The effect of heat treatment condition on mechanical properties and bendability of 6063 aluminium cold-drawn tubes was investigated. The standardized heat treatment presently used in manufacturing of cold-drawn tubes increases the cost and time of the process which ultimately reduces plant productivity. The effects of time, temperature, and furnace heating rate were studied in order to identify an optimized heat treatment for tubes with different cold work levels. Drawn from the as-extruded state, tubes were heat treated to under-aged, peak-aged, and over-aged conditions with time and temperature ranging from 1 min to 24 h and 130–200 °C, respectively. Mechanical properties were determined with full section tensile tests whereas tube bendability was evaluated on an industrial draw bending machine. These characteristics were evaluated in each condition in order to identify the heat treatment which allows conforming to 6063-T832 temper requirements and gives sufficient bendability. Moreover, bendability was successfully correlated to fracture strain measured during a uniaxial tensile test and a threshold value over which problem-free bending operation was determined.

On mechanical properties and superplasticity of Mg–15Al–1Zn alloys processed by reciprocating extrusion

A superior combination of specific strength and low-temperature high-strain-rate superplasticity of two-phase Mg–15Al–1Zn alloys could be achieved with reciprocating extrusion directly from as-cast billets. In the as-extruded state, the yield strength and ultimate tensile strength were 306 and 376 MPa, respectively. The optimum elongation of at least 1610% in company with a high m value of 0.7 was obtained at the strain rate of 1 × 10 −2 s −1 when tested at 325 °C. The pronounced strengthening mechanism was attributed to the high volume fraction of fine-grained hard Mg 17Al 12 phase in the refined α-Mg matrix. The excellent superplasticity at high strain rates was also mainly contributed by the high volume fraction of Mg 17Al 12 phase which displays easier grain boundary sliding than α-Mg phase. The apparent activation energy for superplastic flow is thus smaller than that of the boundary diffusion in Mg. In addition, the mechanisms for the filament formation and cooperative grain boundary sliding are discussed.

Matrix grain refinement in Al–TiAl composites by severe plastic deformation: Influence of particle size and processing route

The microstructure and mechanical behaviour of Al-based composites reinforced with TiAl intermetallic particles has been examined in the as-extruded state and after processing by equal channel angular pressing (ECAP). The latter produces a grain size reduction in the aluminium matrix to values of 500 nm, using route A, and 750 nm, using route C. The ECAP produces up to a 75% increase in the yield stress of the composites, being more rapid when route A is used. The strengthening effect by ECAP is much larger than that obtained by increasing the volume fraction of reinforcement particles from 25 to 50% in these composites.

The influence of Al content and annealing on vibration fracture properties of wrought Mg–Al–Zn alloys

Abstract This study investigated the vibration fracture behavior of two Mg–Zn–Al alloys, AZ31 and AZ61 in as-extruded and as-annealed states. The effects of deformation twins, precipitates and Al concentration on vibration properties were examined. As-extruded AZ31 specimens showed a longer vibration life than the others, mainly because of better damping capacity and a lack of intergranular Mg17Al12 precipitates.

An analysis of thermo-mechanical treatments of a 2618 aluminium alloy: study of optimum conditions for warm forging

The warm formability of a solution-treated 2618 aluminium alloy was investigated by means of torsion tests at temperatures between 423 and 573 K. Dynamic precipitation took place during deformation raising the flow stress and lowering ductility. The flow stresses were substantially higher than those observed by testing the same alloy in the as-extruded state. At the lowest temperatures dynamic precipitation resulted in a continuous increase of flow stress, while above 500 K dynamic precipitation and subsequent coarsening of precipitates resulted in a peak of equivalent-stress versus equivalent-strain curves, followed by softening. These differences in deformational behaviour were attributed to the nature of precipitates, as well as to different kinetics of the ageing processes at each testing temperature.

Aluminum alloy production for the reinforcement of the CMS conductor

The Compact Muon Solenoid (CMS) is one of the general-purpose detectors to be provided for the Large Hadron Collider (LHC) project at CERN. The design field of the CMS superconducting magnet is 4 T, the magnetic length is 12.5 m and the free bore is 6 m. To reinforce the high-purity (99.998%) Al-stabilized conductor of the magnet against the magnetic loadings experienced during operation at 4.2 K, two continuous sections of Al-alloy (AA) reinforcement are Electron Beam (EB) welded to it. The reinforcements have a section of 24/spl times/18 mm and are produced in continuous 2.55 km lengths. The alloy EN AW-6082 has been selected for the reinforcement due to its excellent extrudability, high strength in the precipitation hardened states, high toughness and strength at cryogenic temperature and good EB weldability. Each of the continuous lengths of the reinforcement is extruded billet on billet and press quenched on-line from the extrusion temperature in an industrial extrusion plant. In order to insure the ready EB weldability of the reinforcement onto the pure aluminum of the insert, tight dimensional tolerances and proper surface finish of the reinforcement are required in the as-extruded state. As well, in order to facilitate the winding operation of the conductor, the uniformity of the mechanical properties of the extruded reinforcement, especially at the billet on billet joints, is critical. To achieve these requirements in an industrial environment, substantial effort was made to refine existing production techniques and to monitor critical extrusion parameters during production. This paper summarizes the main results obtained during the establishment of the extrusion line and of the production phase of the reinforcement.

A study on the subgrain superplasticity of extruded Al-Al3Ni eutectic alloy

A directionally solidified Al-Al3Ni eutectic alloy was extruded to obtain micron-size subgrains with [111] fiber texture. The extrusion temperature was varied to have different distributions of the Al3Ni eutectic particles. Choosing the fiber axis as the loading axis, the tensile test results at 500 °C indicate that the elongation is concave downward and strain-rate dependent. Reducing the number of intragranular particles increases the maximum elongation as well as the strain rate of maximum elongation. With the particles residing only intergranularly in the as-extruded state, the maximum elongation, which occurs under the initial strain rate of 6.3×10−3 s−1, is about 300 pct. This subgrain superplasticity is associated with low strain-rate sensitivity but high resistance against strain softening. The fiber texture is always retained, and the microstructure reveals slip of long parallel dislocations. If intragranular particles are also present in the as-extruded state, the occurrence of dislocation tangling and dynamic recovery will give rise to early onset of strain softening and inferior ductility.

Soft magnetic properties of bulk nanocrystalline Fe(Nb, Zr, Hf)B alloys produced by extruding amorphous powders

Utilizing the softening phenomenon of amorphous alloys near the crystallization temperature, we have prepared bulk Fe 84Nb 7B 9, Fe 90Zr 7B 3 and Fe 89Hf 7B 4 alloys by extruding amorphous powders. The extruded bulk alloys are composed of an amorphous phase containing a small amount of bcc phase in the as-extruded state, and the structure changes to a mostly single bcc phase with grain sizes of 10–25 nm by annealing at 923 K. The soft magnetic properties of the bulk nanocrystalline alloys are better for the alloys containing smaller volume fractions of bcc phase in the as-extruded state. This is presumably because the pre-existing bcc grains in the as-extruded state cause an inhomogeneous nanostructure after annealing. Of the three alloys, Fe 90Zr 7B 3 shows the best tendency to consolidate to the bulk form, with a high relative density above 99%, even by extrusion at a relatively low pressure P e = 860 MPa. This alloy exhibits the highest effective permeability μ e = 2350 at 300 Hz and flux density B 800 = 1.59 T, and the lowest H c = 26 A/m.

Strength and ductility of Fe40Al alloy prepared by mechanical alloying

The mechanical behaviour of an alloy based on Fe40Al prepared from mechanically alloyed powders was examined over a wide temperature range in the fine-grained, as-extruded state as well as after recrystallizing to a large-grained state. While the fine-grained material was strong and reasonably ductile at room temperature, in contrast with the weaker and more brittle large-grained material, at high temperature the strength fell to low values, similar for both materials. This behaviour is interpreted in terms of a contribution to strengthening due to the particles present, by Orowan hardening at low temperatures and by dislocation-particle interactions at high temperature, a contribution due to the grain size, which can harden at low temperatures and soften at high temperatures, and a contribution due to the matrix. The room temperature ductility seems to be dependent mostly on the grain size, since fine grain sizes can inhibit brittle crack formation.

The effect of quenching on the mechanical properties of powder metallurgically produced AlSiC (particles) metal matrix composites

Several factors contribute to the strengthening in particulate metal matrix composites (MMCs); their interdependence makes the elaboration of an exhaustive explanation of the phenomenon difficult. In the present work, a comparison between different powder metallurgically produced MMCs consistency of an aluminium matrix reinforced with SiC particles, both in the as-extruded state and in the quenched state, is carried out. Data concerning two powder metallurgy processes, four average particle sizes and four volume fractions of the reinforcement are analysed and compared with the unreinforced matrix. Such analysis allows a deeper understanding both about the result of the mismatch in between the thermal expansion coefficients of the matrix and of the reinforcement on dislocation density, and about the AlSiC solid state reaction. These phenomena act on the strengthening mechanism. Their effect is very specific, because it strongly depends on the SiC particle average size and volume fraction. So, the difference between the ultimate tensile strengths of the as-extruded composites and the quenched composites can change case by case. Sometimes, the improvement in mechanical properties is excellent. This gives well-grounded encouragement in study and design of a suitable heat treatment for such MMCs.