Extrusion of the magnesium-nickel alloys (original) (raw)
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Materials Science and Engineering: A, 2009
Extrusion of the DC-cast alloy AZ80 has been performed at three extrusion ratios (12, 22 and 44) in the temperature range 175 • C ≤ T ≤ 350 • C. Upon extrusion, the as-cast coarse grains undergo pronounced grain refinement and the -phase constituents form stringers in the extrusion direction. The activation of twinning at low extrusion temperatures promotes nucleation of the recrystallized grains at the twin interfaces and refines the grains size. The higher extrusion ratio increases the extrusion velocity and therefore raises the die exit temperature, which results in a slightly coarsen grain size. The unidirectional deformation and DRX during extrusion leads to a fibrous type of crystallographic texture, which results in anisotropy of the yield stress under tension and compression, usually called "strength differential effect" (SDE). The impact of the SDE weakens by lowering the extrusion temperature and remains unaffected by the variations in the extrusion ratio.
Advanced Materials Research, 2012
The effects of heat treatment on the microstructure, tensile property and fracture behavior of as-extruded AZ91 magnesium alloy were studied with OM and SEM. The results show that the grains of as-cast AZ91 alloy are refined by hot extrusion due to dynamic recrystallization, and the mechanical properties are improved obviously. The ductility is significantly enhanced after solution treatment of the as-extruded AZ91 alloy, tensile strength is almost the same as before, and hardness is significantly reduced after solution treatment and artificial aging treatment. The tensile strength reduced and the ductility is significantly enhanced of as-extruded after annealing processes. The fracture surface of as-extruded AZ91 magnesium alloy has the mixed modes of ductile and brittle characteristics. But after T6 or annealing treatment, the dimple number increases evidently.
The Influence of Conventional or KOBO Extrusion Process on the Properties of AZ91 (MgAl9Zn1) Alloy
Materials
Designers’ efforts to use the lightest possible materials with very good mechanical properties mean that in recent years magnesium alloys have been increasingly used. It is well-known that the use of various plastic working processes allows achieving even better strength properties of the material, often without significant loss of plastic properties in relation to the properties of products obtained in the casting process. The article presents the results of research on microstructural changes and mechanical properties of the alloy AZ91 (MgAl9Zn1) occurring in samples subjected to conventional plastic deformation and the KOBO method. The obtained results were compared to the properties of reference samples, i.e., cast samples. The article presents the advantage of using the low-temperature KOBO method compared to the high-temperature deformation in a conventional manner. Moreover, it has been shown that the use of KOBO extrusion allows the alloy AZ91 (MgAl9Zn1) to obtain superplast...
Effect of materials and temperature on the forward extrusion of magnesium alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
Magnesium alloys are being extensively used in weight-saving applications and as a potential replacement for plastics in electronic and computer applications. However, processing of magnesium has always been a challenge for manufacturing industries owing to their high brittleness despite their good EMI shielding property and high specific strength. Despite these advantages, they are limited by their processability. The present work aims to evaluate lower temperature formability of magnesium alloys. Three different materials were selected for axisymmetric extrusion tests, namely AZ31, AZ61 and the forging alloy, ZK 60. To establish the size and capacity of the press required to perform these forming trials and to know the formability, simulation using finite element analysis was carried on a representative material AZ31 using the properties established based on earlier work. A die set with a die shoe was designed to perform the forward extrusion trials. The area reduction ratio for forward extrusion was fixed at 41% for the die design and simulation. The maximum strain is given as ln(A o /A f ) ∼ 0.88 in the case of forward extrusion. The temperature was varied with a temperature controller built in-house from room temperature (RT) to 300 • C. However, the results provided below only include the tests carried out at RT, 100, 150, 175 and 200 • C. Although the forming trials were successful above 200 • C, there was difficulty in removing the specimens from the die cavity. Secondly, the process of removing the samples in the case of AZ31 and ZK 60 resulted in cracking, so it was difficult to evaluate the samples and the process. However, AZ61 samples did not show any evidence of crack formation during ejection of the formed sample. Simulation results and experimental trials showed that magnesium (AZ31) could be easily formed at elevated temperatures of 300 • C. Though there was a good correlation on the yield point prediction between simulation and experimental results, the extrusion loads were higher.
Microstructure and Mechanical Properties of an Extruded Mg-2Dy-0.5Zn Alloy
Microstructure and mechanical properties of an extruded Mg-2Dy-0.5Zn (at.%) alloy during isothermal ageing at 180 • C were investigated. Microstructure of the as-extruded alloy is mainly composed of α-Mg phase, 14H long period stacking order (LPSO) phase and small amounts of (Mg, Zn) x Dy particle phases. During ageing, the 14H LPSO phase forms and develops and its volume fraction increases with increasing ageing time. Tensile test showed that the peak-aged alloy exhibits similar yield and ultimate tensile strengths and elongation to failure at room temperature, 100 • C and 200 • C, but excellent elevated temperature strengths at 300 • C as compared to the as-extruded and over-aged alloys. The analysis showed that the excellent elevated temperature strengths of the peak-aged alloy are attributed to the LPSO phase strengthening and the grain refinement strengthening, and the role of the LPSO strengthening is related to not only its amount, but also its morphology.
The main aim of this paper is to evaluate the effects of hot working (extrusion) and hest treatment on room temperature mechanical properties of magnesium-based AZ91 alloy. The results were compared with as-cast condition. The examined material had been obtained by gravity casting to permanent moulds and subsequently subjected to heat treatment and/or processed by extrusion at 648 K. Microstructural and mechanical properties of properly prepared specimens were studied. R m , R p02 and A 5 were determined from tensile tests. Brinell hardness tests were also conducted. The research has shown that hot working of AZ91 alloy provides high mechanical properties unattainable by cast material subjected to heat-treatment. The investigated alloy subjected to hot working and subsequently heat-treated has doubled its strength and considerably improved the elongation -compared with the as-cast material.
Effect of Extrusion on Microstructure of AZ31 Type Magnesium
European Journal of Technic, 2017
The use of magnesium as structural engineering material has been becoming more widespread. It promises an important future as a main structural material especially in fields such as aviation and automotive because of its higher mechanical properties and lower weight. In this study, the microstructure of extruded AZ31 type material was investigated. The change of grain size was examined by using optical microscope and SEM microscope and EDX data mapping were obtained. The change in the microstructure was investigated. It was observed that grain size was reduced after extrusion and the alloy elements' distribution was homogeneous.
Materials Chemistry and Physics, 2018
The microstructure, texture and mechanical properties of Mg-6wt%Zn-0.5wt%Zr (ZK60) alloys with different La contents (0, 0.5 and 1 wt%) were investigated. The alloys were produced by lowpressure die casting and extruded at 300 °C and 400 °C, following homogenization at 400 °C for 24 h. La addition to ZK60 alloy resulted in a formation of Mg-Zn-La ternary phase, generating a semicontinuous network structure in their as-cast state. After extrusion, secondary phases were broken into fine particles distributed along the extrusion direction. These fragmented particles led to a nucleation of new grains around them i.e. particle stimulated nucleation (PSN), and promoted dynamic recrystallization (DRX) during extrusion. Therefore, increasing La content led to an increase in DRX fraction. Higher extrusion temperature resulted in larger DRXed grains and higher DRX fraction. The basal texture intensity was also decreased with increasing La addition and extrusion temperature by PSN mechanism and solute atoms of La. The ZK60-1La alloy extruded at 300 °C showed a superior yield strength of 311 MPa and ultimate tensile strength of 360 MPa as a result of significant grain refinement and dispersion strengthening. Increasing extrusion temperature resulted in a decrease in yield and ultimate tensile strengths and increase in ductility.
Reciprocating extrusion of rapidly solidified Mg–6Zn–1Y–0.6Ce–0.6Zr alloy
Journal of Materials Processing Technology, 2007
Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr alloy was prepared by reciprocating extrusion (RE) from rapidly solidified (RS) comminuted ribbons. Tensile tests were performed at a strain rate of 4.0 × 10 −4 s −1 and the engineering stress-strain curve contained two distinct yield regions. The first yield region had an upper and a lower yield point. Tensile yield strength of 336 MPa and elongation of 27% were achieved. The microstructures were analyzed with optical microscope, SEM and TEM. The average grain size of the matrix was ∼1.2 m, and the dimension of the strengthening particles, homogeneously dispersed within the matrix, was ∼50 nm. The dimpled tensile fractures observed are characteristic of ductile fracture.
Improving the mechanical properties of extruded Mg–3Al–1Zn alloy by cold pre-forging
Scripta Materialia, 2013
This study demonstrates that cold pre-forging (CPF) conducted before extrusion is a promising means for improving the mechanical properties of extruded magnesium alloys. The CPF process induces numerous twins in the billet, which in turn provides nucleation sites for dynamic recrystallization during extrusion, leading to an increase in the dynamically recrystallized (DRXed) fraction of the extruded alloy. This process increases the uniformity of the DRXed grain structure, thereby improving the strength and ductility of the extruded alloy.