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.
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.
In the present study, the Al 6061/Mg ZK60/Al 6061 composite sheets with the trapezoidal shaped intermediate layer were successfully obtained by multi-pass hot roll bonding. The microstructure and ...mechanical properties of the composite sheets under different rolling passes were investigated. The results demonstrated that the interface of the composite sheets achieved the strong interface metallurgy bonding, without discernible voids, cracks, and other defects. The introduction of the three-dimensional (3D) interface layer significantly improved the interface bond strength of the composite sheets. The interface layer composed of Al3Mg2 and Al12Mg17 was observed at the interface of the composite sheets. The thickness of the intermetallic compounds (IMCs) layer varied with the position of the interface, and the IMCs layer was the thinnest near the center of the sheet. The IMCs layer was continuously coarsening and fragmenting with the increase of rolling deformation, and stress concentration was easily generated at the interface between the Mg layer and the Al layer, so the crystal grains were more refined than that inside of the component sheets, which made the actual strength of the composite sheets higher than the theoretical strength. With the proceeding of the rolling process, the internal grain size of the component sheet gradually increased, and the interface products were coarsened and fragmented, which reduced the tensile properties of the composite sheets. The interface layer with moderate thickness and intact interface layer in the composite sheets appeared uniformly broken when it was under tensile stress, and the direction of microcracks generated was perpendicular to the tensile direction, which hindered the crack propagation and delayed the fracture of the composite materials and thereby enhanced the elongation of the composite sheets. Simultaneously, the trapezoidal shaped intermediate layer made the cracks deflect along the interface, which was conducive to the strengthening and toughening of the interface area, to improve the plasticity of the composite sheets.
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.
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.
A low mass fraction of TiC nanoparticles was successfully introduced into a Mg-4Zn-0.5Ca matrix alloy using mechanical stirring together with ultrasonic treatment. As the mass fraction of TiC ...nanoparticles increased, the grain size of the matrix was gradually reduced, while the concentrations of the MgZn and Ca2Mg6Zn second phase particles were decreased. This indicated that the externally applied TiC nanoparticles could refine the matrix grains and retard the formation of MgZn and Ca2Mg6Zn3 during solidification. The introduction of the TiC nanoparticles and the precipitation of nano-sized MgZn2 contributed to the refined recrystallized grains after low temperature slow-speed extrusion. The total volume fraction of the nano-sized reinforcement consisted of TiC nanoparticles and nano-sized precipitates MgZn2 was more than 3%, which was higher than in previously developed magnesium matrix nanocomposites. The yield strength, ultimate tensile strength and elongation of the as-extruded 1 wt% nanocomposite were 369.8 MPa, 393.6 MPa and 6.7%, respectively. This excellent tensile strength was mainly associated with high mass fraction of nano-sized precipitates as well as the added TiC nanoparticles.
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•Low mass fraction of TiC nanoparticles was introduced into the matrix alloy.•High content of nano-sized MgZn2 were precipitated extruded at 190 °C/ 0.01 mm/s.•YS of ∼369.8 MPa and UTS of ∼393.6 MPa were obtained in the 1 wt% nanocomposite.
Pure titanium particles reinforced Mg–6Zn-0.2Ca magnesium matrix composites were fabricated by semi-solid stirring casting followed by hot extrusion in this work. The microstructures and mechanical ...properties of the Mg–6Zn-0.2Ca alloy and its composites were studied. The Ti particles in as-extruded composites are significantly elongated along the extrusion direction. The average aspect ratio of Ti particles increases while the average size decreases, with the extrusion temperature decreasing. Ti particles promote the dynamic recrystallization of the matrix alloy, break the long-strip Ca2Mg6Zn3 phases and refine the size of MgZn2 phases in the Mg–6Zn-0.2Ca matrix, especially for low extrusion temperatures. The Tip/Mg–6Zn-0.2Ca composite extruded at 240 °C exhibited a high yield strength (YS) of 383.6 MPa with an ultimate tensile strength (UTS) of 404.8 MPa and a decent elongation to failure (EL) of 4.8%. The high strength is associated with fine grains, nano-precipitates as well as Ti particles. In addition, the work hardening rate of Tip/Mg–6Zn-0.2Ca composite is higher than that of Mg–6Zn-0.2Ca alloy at the early stage of plastic deformation due to the combined effects of the elongated Ti particles, the grain refinement and nano-scale MgZn2 precipitates. However, the work hardening rate of the composite decreases faster owing to dislocations cross-slip. And the composite is easier to soften, which results from grain boundary sliding of fine grains and work hardening of deformable Ti particles.
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•The Ti particles are elongated significantly in Tip/Mg–6Zn-0.2Ca composites along extrusion direction after hot extrusion.•The Tip/Mg–6Zn-0.2Ca composite exhibited a high yield strength of 383.6 MPa with an ultimate tensile strength of 404.8 MPa and a decent elongation to failure of 4.8%.•The strain hardening rate of Mg–6Zn-0.2Ca matrix increased by the addition of Ti particles.•Dislocation slip inside Ti particles plays an important role in the softening of Mg–6Zn-0.2Ca matrix during the process of plasitic deformation.
•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.
In order to find suitable degradable materials for the fracturing ball of wolf howl, a new as-cast Mg-4Zn-xNi (x = 0.5, 1, 2, 4 wt.%) alloys were prepared. Results indicated that the addition of Ni ...element lead to the formation of Mg2Ni phase in the Mg-4Zn-xNi alloys, which responsible for the increase of compressive strength and micro-hardness of Mg-Zn series alloy. Nevertheless, formation of Mg2Ni phase with high electrochemical potential can also accelerate the degradation rate of Mg-Zn series alloy. Accompanied with the increasing Ni content, the amount of Mg2Ni phase increases simultaneously, which aggravate galvanic corrosion and results in the higher degradation rate of Mg-Zn series alloys. The Mg-Zn-Ni alloy with moderate strength and higher degradation rate are obtained in present work, which is thought as an ideal candidate for the fracturing ball of wolf howl.
•Addition of Ni is propitious to improve the degradation rate of Mg-Zn series alloy.•Formation of Mg2Ni phase is the reason for the rapid degradation rate of Mg-Zn-Ni alloys.•The present Mg-Zn-Ni alloys exhibit the fastest degradation rate among the reported work in the reference.
The present work mainly focuses on the regulation of the bimodal microstructure (fine recrystallized grains and elongated un-recrystallized grains) on the work hardening and softening behaviors of ...Mg-6Zn-1Gd-0.3Ca alloy. Meanwhile, the grain refinement mechanism was discussed through EBSD. The results show the work hardening capacity of the alloy increases with improving the volume fraction of fine recrystallized grains, which is mainly due to the increase of dislocation storage rate caused by grain coarsening. The stress reduction (∆P1) value in the early stage of tensile deformation is the biggest for the alloy with fine recrystallized grains of ∼66.8 %, which is attributed to the greater stored energy can provide greater driving force for softeing effect. However, the stress reduction (∆Pi(i=2,3,4)) values of the alloys in the later stage of tensile deformation decrease monotonically with the increase of fine recrystallized grains amount. Moreover, the analysis shows that the fine recrystallized grains of Mg-6Zn-1Gd-0.3Ca alloy are mainly formed by dynamic recrystalliztion (DRX).
•The most of the fine equiaxed grains in the as-extruded Mg-6Zn-1Gd-0.3Ca alloys come from DRX, and a small amount are formed by SRX.•The work hardening effect of the as-extruded Mg-6Zn-1Gd-0.3Ca alloys increases with the increase of extrusion temperature.•The highest stored energy of the alloy extruded at 300 °C in the early stage of plastic deformation causes the highest ∆P1 value. However, the ∆P2, ∆P3 and ∆P4 values of the as-extruded alloys decrease monotonically with the extrusion temperature increases from 260 °C to 340 °C, which are mainly attributed to that the grain size and secondary phase amount of the as-extruded Mg-6Zn-1Gd-0.3Ca alloy increase with the increase of extrusion temperature.
