Post-extrusion Heat Treatment Research Articles

Effect of various post-extrusion tempering on performance of AA2024 tubes fabricated by shear assisted processing and extrusion

• Extrusion speed of ShAPE for AA2024-T371 billets reaches 7.4 m/min. • The yield strength of the AA2024-T8510 ShAPE-extruded tube is 32% higher than typical ASM and minimum ASTM values. • The elongation at break of ShAPE-extruded AA2024-T8510 tubes is doubled than typical ASM and minimum ASTM values. Aluminum alloy 2024 tubes were extruded using the shear assisted processing and extrusion (ShAPE) method. Extrusions were produced at 7.4 m/min at 482 °C using the ShAPE technique which is more than doubles the previous highest extrusion speed for AA2024 using conventional extrusion methods. Standard T3510 and T8510 post extrusion heat treatments were applied to improve the mechanical performance of ShAPE extruded AA2024 tube. The ultimate tensile and yield strength of the AA2024-T8510 ShAPE-extruded tube are 522.0 ± 3.3 MPa and 510.7 ± 3.3 MPa, which are respectively 18% and 32% higher than typical ASM International and minimum American Society for Testing and Materials (ASTM) values. The elongation at break of ShAPE-extruded AA2024-T8510 tubes is two times higher than the typical ASM International and minimum ASTM values. This improved ductility is attributed to the refinement of grain size and secondary phases as well as the uniform dispersion of sub-micron strengthening precipitates formed during the ShAPE processing.

Effect of heat treatment on the galvanomagnetic properties of bulk nanostructured samples of Bi85Sb15 solid solution

Extruded bulk nanostructured samples of Bi85Sb15 solid solution from particles with average sizes ∼ 2.105; 950; 650; 380; 30 and 15 nm were obtained and investigated their galvanomagnetic properties in the range of ∼ 77-300 K. Were investigated samples that have not passed heat treatment, and the same samples that have passed heat treatment. It was found that the electrical and thermal properties of Bi85Sb15 solid solution samples significantly depend on the size of nanoparticles and post-extrusion heat treatment. Heat treatment leads to a decrease in the concentration of current carriers and to an increase in the mobility of current carriers and the total thermal conductivity of the samples under study, which is mainly due to the electronic component of thermal conductivity. The change in thermal parameters is satisfactorily explained by changes in occurring in the structure of samples during extrusion and heat treatment and correlates well with changes in the electrical parameters of these processes.

The Effect of Rod-Shaped Long-Period Stacking Ordered Phases Evolution on Corrosion Behavior of Mg95.33Zn₂Y2.67 Alloy.

The morphology evolution of long-period stacking ordered (LPSO) phases on corrosion behavior of Mg95.33Zn2Y2.67 alloy is investigated systematically during as-cast, pre-extrusion heat-treated, as-extruded and post-extrusion heat-treated conditions. The second phases in the as-cast alloy are only LPSO phases with a few Y particles. The pre-extrusion heat treatment changed LPSO phases from blocks into a rudimentary rod shape with lamellar structure, subsequently into fine fragments by extrusion, and then into a regular rod shape with lamellar structure followed by post-extrusion heat treatment. Immersion tests and electrochemical measurements in 3.5 wt % NaCl solution reveal that the post-extrusion heat-treated alloy has the best corrosion resistance with the lowest corrosion rate. This is attributed to the rod-shaped LPSO phases, which could hinder corrosion proceeding, and result in corrosion orientated along the direction of rods and forming relatively dense long-strip corrosion products. Our findings demonstrate that the improved corrosion resistance of magnesium alloys with LPSO phases can be tailored effectively by the proceeding technology and post-heat treatment.

Post-extrusion heat-treatment as a facile method to enhance the mechanical properties of extruded xylan-based polymeric materials

Hemicelluloses are among the most abundant renewable polymers in nature, and their processing into biodegradable polymeric materials via extrusion was recently reported as a novel alternative technique for solvent casting. A simple heat-treatment step conducted after the extrusion of corn cob xylans was found to enhance the mechanical properties of strips by altering their moisture absorption behavior. Depending on the heat-treatment temperature, which varied between 60 °C and 150 °C, xylan-based strips with an ultimate tensile strength greater than 120 MPa, elongation at break of around 30% and elastic modulus of approximately 1.2 GPa were obtained. The equilibrium moisture content of the strips decreased with increasing heat-treatment temperature. Considering that water acts as a plasticizer for hemicellulose based materials, the changes in the mechanical properties were found to be associated with the changes in the equilibrium moisture contents of the strips.

Effects of Partial Phase Transformation on Characteristics of 9Cr Nanostructured Ferritic Alloy

The core structures of future nuclear systems require tolerance to extreme irradiation, and some critical components, for example, the fuel cladding in Sodium-cooled Fast Reactors (SFRs), have to maintain mechanical integrity to very high doses of 200 -400 dpa at high temperatures up to 700 degrees C. The high Cr nanostructured ferritic alloys (NFAs) are under intense research worldwide as a candidate core material. Although the NFAs have some admirable characteristics for high-temperature applications, their crack sensitivity is very high at high temperatures. The fracture toughness of high strength NFAs is unacceptably low above 300 degrees C. The objective of this study is to develop processes and microstructures with improved high temperature fracture toughness and ductility. To optimize the afterextrusion heat treatment condition, both the computational simulation technique on phase equilibrium and the basic microstructural and mechanical characterization have been carried out. 9 Cr-NFA was produced by the mechanical alloying of pre-alloyed Fe-9Cr base metallic powder and yttria particles, and subsequent extrusion. The post-extrusion heat-treatments of various conditions were applied to the asextruded NFA. The tensile and fracture toughness tests were conducted for as-extruded and heat-treated samples at up to 700 degrees C. Fracture toughness of the NFA has increasedmore » by more than 40% at every testing temperature after heat-treatment in the inter-critical temperature range. The increment of fracture toughness of the NFA after post-extrusion heat-treatment is attributed to the increased strength at below 500 degrees C, and an increased ductility at 700 degrees C.« less

Influence of pre- and post-extrusion heat treatments on microstructure and anisotropy of mechanical properties in a Mg–Al–Zn alloy

The pre-extrusion homogenization treatment at 400°C effectively dissolves the eutectic phase and the liberated Al contributes in solid solution strengthening. After extrusion with prior homogenization, an abnormal grain growth occurs at the region favored by the local degree of dynamic recrystallization (DRX) and texture. This weakens the bulk texture, reduces the directional anisotropy in yield Stress and eliminates the strength differential effect without any loss of yield stress. The secondary recrystallization during post-extrusion annealing at 400°C leads to pronounced grain growth, the texture is profoundly weakened and the yield stress becomes isotropic but is reduced by 33%.

Severe plastic deformation of Ti74Nb26 shape memory alloys

Abstract Severe plastic deformation of Ti74Nb26 shape memory alloy was conducted successfully at room temperature using equal channel angular extrusion (ECAE). In conjunction with short post-extrusion heat treatments, ECAE improved the maximum transformation strain of the alloy from 1% to 1.7%. Moreover, it drastically reduced the irrecoverable strain during constant-stress thermal cycling experiments. After identical heat treatments, the specimens processed by one pass ECAE possess both higher transformation strain and higher irrecoverable strain as compared to those processed by four pass ECAE. However, the difference between the crystallographic texture contributions to the transformation strains of these specimens was minimal, and thus, the shape memory characteristics are believed to be influenced mainly by microstructural features. High dislocation density, small grain size, and precipitation of the omega phase were found to reduce not only the irrecoverable strain, but also the transformation strain.

Production of wire via friction extrusion of aluminum alloy machining chips

This paper describes the production of fully consolidated wires from aluminum alloy AA2050 and aluminum alloy AA2195 machining chips via the friction extrusion process. In this work, the extrusion rate was linearly related to the power input/die rotational speed. Hot crack and cold crack defects appeared on wires produced using either too high or too low a power input/die rotational speed. The extruded wire microstructure consisted of fully equiaxed, recrystallized grains. Average grain size in the wires generally increases with the increase of die rotational speed/extrusion power. Micro-hardness was homogeneous across the wire transverse cross-sections. Positive response to post-extrusion heat treatment was observed with increasing extrusion power indicating increasing temperature and in process solution heat treatment of the wire with sufficient extrusion power. The ductility of defect free wire was demonstrated by the absence of cracking in 5T bend tests.

The Serrated Flow Behavior of Mg-Gd(-Mn-Sc) Alloys

The tensile deformation behavior of extruded samples of Mg-0.8 pct Gd and Mg-0.8 pct Gd-0.5 pct Mn-0.45 pct Sc (at. pct) alloys has been studied. Both alloys exhibit serrated flow when they are tensile tested at temperatures ranging from 150 °C to 300 °C and at strain rates of 1.67 × 10−4 s−1 to 1.67 × 10−2 s−1, and this serrated flow behavior is significantly affected by postextrusion heat treatments. Combined with observations made by transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP), the serrated flow is attributed to dynamic interactions between solute atoms and gliding dislocations. It is suggested that Gd atoms in the solid solution matrix of magnesium are mainly responsible for the serrations in the two alloys. The additions of Mn and Sc to the Mg-Gd alloy strengthen the dynamic solute-dislocation interactions and lead to a lower critical strain and larger stress drops of the serrated flow in the Mg-Gd-Mn-Sc alloy.

Effect of composition and cooling rate on the transformation of α to γ phase in TiAl alloys

Microstructure controls mechanical properties of TiAl-based alloys and it does so in three ways: alloy composition, thermomechanical (dynamic), and static heat treatments. This study considers the effect of composition and cooling rate in the transformation temperature from hcp-α phase to fct-γ phase in the α and γ phase field. The data for three Ti–46Al–4–8Nb alloys show that α and γ transformation temperature varies by 70 °C by changing the cooling rate over a factor of 40. Compared to the effects of cooling rate, the effect of composition on the α–γ transformation is minimal. Microstructural examination following a change in cooling rate from the post-extrusion heat treatment reveals differences in the desired lamellar structure and suggests the alloy composition and heat treatment cooling rate for optimal properties.

An integrated study on the effect of pre- and post-extrusion heat treatments and surface treatment on the filiform corrosion properties of an aluminium extrusion alloy

The effect of pre- and post-extrusion heat treatments on the filiform corrosion behaviour of a well-known aluminium extrusion alloy AA6063 is studied by a combination of accelerated filiform corrosion exposure tests and potentiodynamic polarisation measurements for four different surface treatments. It is shown that the post-extrusion heat treatment of this AlMgSi alloy can influence the filiform corrosion properties significantly, in particular for the milder surface treatments. In contrast, the relative effect of the pre-extrusion treatment on the filiform corrosion properties is minimal for all treatments. The alloys are most susceptible to filiform corrosion in the β′ condition. The susceptibility decreases with coarsening of the Mg 2Si particle distribution. For the post-extrusion heat and surface treated AA6063 material a clear correlation between the polarisation characteristics and the two principal filiform corrosion characteristics, i.e. the propagation rate and total area of attack after accelerated exposure, is observed. The observed correlation is attributed to a pitting corrosion mechanism with a rate depending on the (coupled) Mg 2Si precipitate size and fraction.

Microstructures and properties of a hot-extruded TiAl containing no Cr

Microstructures and tensile properties of the TiAl alloy CTI-8, with the composition of Ti–47Al–(2–4)Nb–(0.5–1.0)W–(0.08–0.18)B (at.%) were studied by hot extrusion at various temperatures below and above T α (=1315 °C). Both extrusion temperature and boron concentration are important in controlling lamellar structures in the alloy. Uniform grain structures were formed in the alloy with >0.1% B, whereas abnormal grain growth was observed in the alloy containing less B and hot extruded at temperatures above 1350 °C. Electron microprobe studies revealed a non-uniform distribution of W and Nb in the extruded alloy, presumably due to the initiation of phase transformations involving the redistribution of these alloying elements in the α and γ phases during cooling from the extrusion temperatures. Tensile properties at room and elevated temperatures are sensitive to microstructure and boron addition. The post-extrusion heat treatment at 1315 °C moderately lowers the yield strength but substantially increases the tensile ductility of CTI-8. Grain size is the key parameter in controlling the room-temperature ductility of TiAl alloys with and without Cr additions. Boron does not affect the yield strength but lowers the ductility of CTI-8 containing >0.10% B. In comparison, hot-extruded CTI-8 is substantially stronger and much more ductile than other advanced TiAl alloys with lamellar and duplex structures.

Effects of process variables on mechanical properties of extruded Al-Cr-Zr base rapidly solidified alloy particulate

Results for tensile properties and hardness of a series of extrusions of Al-Cr-Zr base alloy particulates show that, while extrusion or thermal exposure at relatively high temperature significantly reduces strength and hardness, extrusion ratio in the range 16 to 30:1 at 300°C or post-extrusion heat treatment at this temperature has relatively little effect. Results for the range of alloy compositions and process conditions investigated correlate well with the relationships σ= K 1 H v and logε f= K 2 H v , where K 1=2.9±0.2 and 3.5±0.2 for 0.2% proof strength respectively and K 2=140±30 (σ in MPa, H v in kg/mm 2 and elongation to fracture ε f in percent).

Microstructure and properties of extruded Al–Li–Cr alloy prepared from atomised powder

The microstructural evolution and resulting mechanical properties of an Al–2·7Li–1·0Cr alloy produced by hot extrusion of inert gas atomised powder is reported. The response of the material to various heat treatments is also investigated. All of the extrudates exhibit a dynamically recovered substructure, but the extrusion temperature is shown to have a significant effect on the nature and distribution of the precipitates present. At the lower temperatures (<350°C) there is evidence of δ precipitation together with an Al–Cr phase (probably Al7Cr). The higher extrusion temperatures yield greater quantities of the Al–Cr phase in a bimodal distribution, but δ is no longer present. In general, the post-extrusion heat treatment involving a high temperature solution soak at 540°C tends to produce a similar microstructure in all the extrudates consisting of the bimodal Al–Cr precipitate distribution. The tensile strength levels achieved in the peak aged condition (500 MN m−2 0·2%PS and 530 MN m−2 UTS) are comparable to the values reported for 7000 series alloys. However, the corresponding ductility (8% elongation) and fracture toughness values (7 MN m−3/2) are somewhat lower.MST/1057

Influence of thermomechanical processing on elevated temperature slow plastic flow properties of B2 aluminide Fe-39.8at.%Al

A study of the elevated temperature slow plastic flow properties of the B2 aluminide Fe-39.8at.%Al was undertaken. Polycrystalline materials possessing several different microstructures were produced by the hot extrusion of pre-alloyed powder and, in some cases, post-extrusion heat treatments. Compression tests were conducted in air at 1200, 1300 and 1400 K. Such testing revealed that the extrusion temperature affected the active deformation mechanisms where material extruded at 1505 K had a stress exponent about twice that of the intermetallic extruded at 1200 K. Grain size refinement to about 10 μm was found to strengthen the Fe-39.8at.%Al material; unfortunately the effectiveness of such strengthening is limited to a homologous temperature of about 0.75 for strain rates of commercial interest (less than 10 −7 s −1).