The Mg–Ca alloys with 2wt%, 3wt%, 5wt% Al content were fabricated in this paper. After be extruded at 673K with the ratio of 16:1, the microstructures and mechanical properties of the alloys ...influenced by Ca/Al ratio were investigated.Results showed that the category and amount of precipitated secondary phase were influenced obviously by Ca/Al ratio, which changed from Mg2Ca and (Mg, Al)2Ca to Al2Ca as the Ca/Al ratio decreased from 1 to 0.4. Even though the secondary phase was cracked after the application of hot extrusion, the amount, size and distribution of secondary phase were strongly dependent on Ca/Al ratio. The basal plane texture was found in all the as-extruded alloys, the I(101¯0)/I(101¯1) and I(0002)/I(101¯1) values demonstrated different changing tendencies with the variation of Ca/Al ratio. All the UTS, elongation and strain hardening rate of the as-extruded alloys increased with decreasing Ca/Al ratio, however, the YS exhibited the inverse variation tendency. A significant stagnation point was found in the θ-(σ-σ0.2) curve as the Ca/Al ratio is 1, which becomes unobvious with decreasing Ca/Al ratio. The reasons are given and analyzed.
The Mg-4Zn-0.5Ca alloys extruded at 280°C by different ultra-slow extrusion speed (0.01, 0.05, 0.1 and 0.5mms−1) were investigated in present study. The results show that both the volume fraction and ...average size of DRXed grains increase with the increase of extrusion speed, which is different from that depicted by present Z parameter. To fit the extrusion conditions with low temperature and ultra-slow extrusion speed, a more accurate estimate/measurement of the actual temperature in the expression of the Z parameter is needed in the further study. Even though the amount of precipitates decrease with the increasing extrusion speed, the increasing amount of DRX regions lead to the decreased intensity of basal plane texture. Superior mechanical properties with the yield strength of 324.5MPa, ultimate tensile strength of 371.1MPa and elongation to failure of 7.9% are achieved in present Mg-4Zn-0.5Ca alloy extruded at the speed of 0.01mms−1. As the extrusion speed increased from 0.01 to 0.5mms−1, the strength decreases which is accompanied with the increase of elongation.
Ti/Al multilayered composites (LMCs) with 3-layers, 5-layers and 7-layers were prepared by hot‐pressing and hot‐rolling. The effects of the interface on the mechanical properties and stamping ...formability of LMCs were revealed. The results indicate that the TiAl
3
phases at the interface thicken gradually with the increase of layers. As the layers of LMCs increases, both the grain size and the basal texture strength of Ti decrease, and Ti possesses a higher Schmid factors (SF) and more uniform SF distribution, which promotes the overall coordinated deformation of LMCs. The elongation (EL) of LMCs gradually increases at the expense of the strength with the increase of layers. The stress–strain transfer across the interface, the release of residual stress through interfacial microcracks, and the improvement of the interfacial metallurgical bonding strength are all conducive to the coordinated deformation between Ti and Al layers, thus the strength of LMCs decreases and the EL enhances. Both the yield strength ratio (σ
s
/σ
b
) and plastic strain ratio (r) decrease, while the strain-hardening exponent (n) increases with the increase of layers of LMCs, which are beneficial to improve the stamping formability of LMCs. The number of interface increases with the increase of layers, which hinders crack propagation. Moreover, the microcracks are easily induced by the brittle TiAl
3
phase at the interface, and the main cracks deflect obviously and release part energy in the form of secondary microcracks, thus delaying the failure of LMCs and improving their stamping formability.
Graphical Abstract
High strength Mg-9Al serial alloy processed by slow extrusion Kang, Jin-wen; Sun, Xue-fei; Deng, Kun-kun ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
06/2017, Letnik:
697
Journal Article
Recenzirano
The AZ91-0.5Ca alloy was extruded at 250°C with slow extrusion speed (0.03, 0.3, 3mm/s) in the current study. The results showed that both the volume fraction and average grain size of DRXed grains ...increased with the increase of extrusion speed. Furthermore, numerous fine Mg17Al12 phase were observed in the DRXed regions of the extruded alloys, the amount of which decreased by increasing extrusion speed. The decrease of extrusion speed led to the improvement of yield strength and ultimate tensile strength, however, at the expense of elongation. As the extrusion speed decreased to 0.03mm/s, the yield strength, ultimate tensile strength and elongation of present alloy were ~347.8MPa, ~402.2MPa and ~9.1%, respectively, which were superior to the present commercial Mg-Al serial alloys. Detailed reasons are given and analyzed.
The SiCp/Mg-xAl-2Ca composite with different (2, 3, 5 and 9 wt%) Al content is fabricated by stir casting. After be extruded at 673 K with the ratio of 16:1, the microstructures and mechanical ...properties of the composites are investigated. As compared with Mg-xAl-2Ca alloys, the addition of SiCp has no obvious effect on the category of precipitated phase, but increases its volume fraction and is propitious to the uniformity of microstructures. With the application of extrusion, precipitated phase is refined and its distribution is improved obviously. The yield strength of the composites increases with the increasing of Al content as a result of an increased amount of precipitated phase. The ultimate tensile strength and elongation are improved as the Al content increased from 2 wt% to 5 wt%, but deterioration happens when the Al content is increased to 9 wt%. Addition of SiCp lows down the strength of Mg-2Al-2Ca alloy, however, leads to the increased strength of Mg-3Al-2Ca alloy and Mg-5Al-2Ca alloy. Even though the yield strength of SiCp/Mg-9Al-2Ca composite is similar to Mg-9Al-2Ca alloy, it owns a lower ultimate tensile strength.
The 5μm10 vol % SiCp/AZ91 composite was extruded successfully at 250 °C by the slow speed extrusion (0.01, 0.1 and 1 mm/s). Results indicated that the composite with the yield strength of ∼371.5 MPa ...and ultimate tensile strength of ∼443.9 MPa exhibited much higher tensile strength than present particle reinforced magnesium matrix composites (PMMCs). Such high tensile strength in present work might be attributed to ultra-fine grains and submicron sized Mg17Al12 phases precipitated during extrusion. As the extrusion speed increased from 0.01 to 1 mm/s, both the average size of grains and Mg17Al12 phase increased, while volume fraction of Mg17Al12 phase decreased. All these led to the decrease of yield strength and ultimate tensile strength, however, accompanied by the increase of elongation.
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•Ultra-fine grain is achieved by slow-speed extrusion in SiCp/AZ91 composites.•Large amount of fine Mg17Al12 phases precipitate during extrusion process.•Superior strength (YS of 371.5 MPa, UTS of 443.9 MPa) is obtained in present work.•Ultra-fine grain plays a dominant role in such high strength of PMMCs.
We report acute antibody responses to SARS-CoV-2 in 285 patients with COVID-19. Within 19 days after symptom onset, 100% of patients tested positive for antiviral immunoglobulin-G (IgG). ...Seroconversion for IgG and IgM occurred simultaneously or sequentially. Both IgG and IgM titers plateaued within 6 days after seroconversion. Serological testing may be helpful for the diagnosis of suspected patients with negative RT-PCR results and for the identification of asymptomatic infections.
The as-cast Mg-4Zn-2Gd-0.5Ca alloy mainly contained I phase and W phase, while the I phase dissolved into Mg substrate after homogenization treatment which improved the alloy’s corrosion resistance. ...After the application of multidirectional forging (MDF), the grains were refined obviously accompanied with the precipitation of I phase. With the increasing pass of MDF, both the size of dynamic recrystallized grains and the amount of precipitated I phase increased. The corrosion resistance of Mg-4Zn-2Gd-0.5Ca alloy became worse after 1 pass of MDF as compared with the as-homogenizated condition because of the precipitation of I phase. Neverthless, the corrosion resistance of the as-MDFed Mg-4Zn-2Gd-0.5Ca alloy deteriorated with the increasing pass of MDF. As compared with grain refinement, the precipitated I phase is thought to play a main role on the corrosion behavior of Mg-4Zn-0.5Ca alloy.
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•Dissolution of I phase lead to the improved corrosion resistance of as-HTed alloy.•MDF results in the grain refinement and precipitated I phase of Mg-4Zn-2Gd-0.5Ca alloy.•The influence of precipitated I phase on corrosion resistance is larger than grain refinement.
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•Effect of extrusion on corrosion properties of Mg-Al-Ca alloys was studied.•Effect of category of second phase on corrosion behavior in Mg-Al-Ca alloy was studied.•Effect of ...distribution of second phase on corrosion behavior in Mg-Al-Ca alloy was studied.
Effect of extrusion on the microstructures and corrosion properties of Mg-2Ca-χAl (χ=0, 2, 3, 5wt.%) alloys were investigated in present work. Results showed that the precipitated phase changed from Mg2Ca and (Mg, Al)2Ca to Al2Ca with the increase of Al content. Corrosion results indicated that the addition of Al could improve the corrosion resistance of Mg by the formation of protective (Mg, Al)2Ca and Al2Ca. The as-cast alloys showed uniform corrosion mechanism while the as-extruded Mg-Al-Ca alloys presented local corrosion characteristic. Above different corrosion mechanisms were illustrated and analyzed.
•The ideal constructive equation can be applied to SiCp/AZ91 composite is obtained.•The good workability of SiCp/AZ91 composite at low-temperature-regions is obtained.•The Q for hot deformation under ...various conditions is calculated and analyzed.
Hot deformation behavior of fine-grained SiCp/AZ91 composite was investigated at the temperature of 543–693K and strain rate of 0.001–1s−1. Processing maps based on dynamic material model (DMM) were developed at the strain of 0.1–0.5. Both the optimum process conditions and the dominant flow instability mechanism of fine-grained SiCp/AZ91 composite were given and analyzed. To describe the hot deformation behavior of fine-grained SiCp/AZ91 composite more exactly, the stress calculated by three typical constructive equations was compared with the measured value. The results show that the power law is deduced to be the most suitable constructive relationship for fine-grained SiCp/AZ91 composite, which is unlike previous reports. The calculated Q value increases with increasing temperature and strain rate. At 0.001s−1, the deformation mechanism of the composite is deduced to be grain boundary diffusion controlled dislocation climb; while, the deformation mechanism is deduced to be dislocation climb at 0.1–1s−1.
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