联合多向锻造与挤压变形TiC纳米颗粒增强Mg−Zn−Ca基复合材料的组织与力学性能

采用多向锻造(MDF)和挤压(EX)相结合工艺对TiC纳米颗粒增强Mg−4Zn−0.5Ca基纳米复合材料进行变形。与仅单一MDF相比,经MDF+EX变形后纳米复合材料的晶粒尺寸显著减小。当MDF温度为270℃时,随MDF道次的增加,经EX变形后再结晶(DRX)晶粒的平均尺寸逐渐增大;而当MDF温度为310℃时,经EX变形后DRX晶粒的平均尺寸显著减小。经MDF+EX多步变形后纳米复合材料中同时出现细小和粗大的MgZn2相,这些MgZn2相的体积分数随EX前MDF道次的增加而逐渐增大。对温度为310℃经3道次MDF后的纳米复合材料进行EX,其屈服强度、极限抗拉强度和伸长率分别达到~404 MPa,~450.3 MPa和~5.2%。这主要与MDF+EX多步变形后晶粒细化强化及MgZn2析出相引起的Orowan强化有关。

Microstructure and mechanical properties of Mg-4Zn-xGd(x=0,0.5,1,2)alloys

The present work inainly focuses on tlie effect of minor cofiteut of Gd cicmcnt on the micrGstmcturc and mechanical properties of Mg Zn alloy.The Mg-4Zn-xGd(x=0,0.5,1,2)alloys were fabricated and subjected to extrusion at 280℃ with the ratio of 25:1.Results revealed that the addition of Gd could inhibit the dynamic recrystallization(DRX)of Mg-4Zn alloy,and both the size and volume fraction of DRXed grains demonstrated a decreasing tendency as the Gd content increased from 0.5 to 2 wt.%.It is the weakening effect on DRX behavior that lead to the smaller amount of fine precipitate and the stronger texture intensity.As compared with the Mg-4Zn alloy,the yield strength and ultimate tensile strength of Mg-4Zn-xGd alloys were improved obviously by the addition of minor content of Gd,however,at the expense of elongation.Excellent tensile properties with the yield strength of〜369.8 MPa and ultimate tensile strength of〜400.3 MPa were obtained when the Gd content was 2 wt.%.

Microstructure and mechanical properties of a compound reinforced Mg95Y2.5Zn2.5 alloy with long period stacking ordered phase and W phase

The microstructure evolution of Mg100-2xYxZnx(x=2, 2.5, 3, 3.5) alloys was investigated. Results show that the Mg100-2xYxZnx alloys are composed of α-Mg, long period stacking ordered(LPSO) phase and eutectic structure phase(W phase), and the Mg95Y2.5Zn2.5 alloy has the best comprehensive mechanical properties. Subsequently, the microstructure evolution of the optimized alloy Mg95Y2.5Zn2.5 during solidification and heat treatment processes was analyzed and discussed by means of OM, SEM, TEM, XRD and DTA. After heat treatment, the lamellar phase 14H-LPSO precipitated in α-Mg and W phase transforms into particle phase(MgYZn2). Due to the compound reinforcement effect of the particle phase and LPSO phase(18R+14H), the mechanical properties of the alloy are enhanced. The tensile strength and elongation of the Mg95Y2.5Zn2.5 alloy is improved by 9.1% and 31.3% to 215 MPa and 10.5%, respectively, after solid-solution treatment.

Effect of Li on formation of long period stacking ordered phases and mechanical properties of Mg-Gd-Zn alloy

Alloys with composition of Mg_(96-x)Gd_3Zn_1Li_x(at.%)(x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and the mechanical properties were investigated. The results showed that Li is an effective element to refine the grains and break the eutectic networks in as-cast MgGd_3Zn_1 alloy. During solid solution treatment, these broken eutectic networks are spheroidized and highly dispersed. In addition, plentiful lamellar long period stacking ordered(LPSO) phases are precipitated in an α-Mg matrix when the Li addition is not more than 4%. Solid-solution treated Mg_(92)Gd_3Zn_1Li_4 alloy exhibits an optimal ultimate tensile strength(UTS) of 226 MPa and elongation of 5.8%. The strength of MgGd_3Zn_1 alloy is improved significantly, meanwhile, the toughness is apparently increased.

Effect of Ti_(p) Content on the Work Hardening and Softening Behavior of Mg-Zn-Ca Alloy

The Ti_(p)/ZX60 composites with different Ti_(p) contents were prepared by semi-solid stirring casting.After extrusion,the microstructure,work hardening and softening behavior of the Ti_(p)/ZX60 composites were analyzed compared with the ZX60(Mg-6Zn-0.2Ca)alloy.The results showed that the addition of Ti_(p) could not only promote the nucleation of dynamic recrystallized(DRXed)grains,but also be propitious to the refinement of DRXed grains.With increasing Ti_(p) content,the size of DRXed grains decreased accompanied with increasing volume fraction of DRXed grains.As the Ti_(p) content increased to 15 vol.%,the average size and volume fraction of DRXed grains reached to~0.32μm and 93.2%,respectively.Besides,both the strength and elongation were improved by the addition of Ti_(p).With increasing content of Ti_(p),a substantial increase in the strength was achieved with little change in the elongation.However,the elongation decreased sharply when the Ti_(p) content further increased to 15 vol.%.The addition of Ti_(p) led to an increase in the work hardening rate,which gradually increased with increasing Ti_(p) content.However,the softening rate did not demonstrate the same tendency with increasing Ti_(p) content.Unlike the conventional ceramic particles,the Ti_(p) can be deformed in coordination with the matrix alloy,which imparted a higher softening rate to the matrix alloy.Even though the softening rate improved as the Ti_(p) content increased from 5 to 10 vol.%,it dropped deeply as the Ti_(p) content increased to 15 vol.%owing to the fracture of Ti_(p) during extrusion.

Recent Research on the Deformation Behavior of Particle Reinforced Magnesium Matrix Composite: A Review

Particle reinforced magnesium matrix composite(PMMC) possesses the merits of high specific strength, high specific modulus, better dimensional stability, good wear resistance and lower production cost, which is thought as a promising material in the field of aerospace, automobile, electronic communication, etc. To eliminate the casting defect, the PMMC is usually experienced hot deformation process. The present paper mainly focuses on the deformation behavior of PMMCs. First, the development of PMMCs based on particle size is introduced. Then, the hot deformation technology and deformation mechanism of PMMCs at elevated temperature are given and analyzed, respectively. After reviewing the dynamic recrystallization and texture of PMMCs, its future development is suggested based on the current research progress.

Corrosion Resistance of AZ91 Mg Alloy Modified by High-Current Pulsed Electron Beam

The high-current pulsed electron beam(HCPEB) treatment with current density 6 J/cm^2 was applied on AZ91 Mg alloy to improve its corrosion resistance. Results showed that the net-like Mg_(17)Al_(12) disappeared on the surface of AZ91 Mg alloy after irradiation by HCPEB, which was instead of supersaturated Al element on the surface. Nevertheless, the application of HCPEB also led to the formation of crater-like and groove-like structures as well as micro-cracks on the surface of AZ91 Mg alloy. After HCPEB treatment by 3, 5 and 10 pulses, the AZ91 Mg alloy exhibited better corrosion resistance.However, the increasing amount of micro-cracks reduced the anti-corrosive properties of AZ91 Mg alloy as the pulse increased to 20 and 30.

Effect of Precipitated Phases on Corrosion of Mg95.8Gd3Zn1Zr0.2 Alloy with Long-Period Stacking Ordered Structure

The microstructure of the precipitated phases of Mg95.sGd3Zn1Zro.2 alloys with long-period stacking ordered structure before and after heat treatment is discussed. The corrosion properties of the as-cast （F）, solid-solution （T4） and aging-treated （T6） alloys in 1% NaC1 solution are studied. The hydrogen evolution and electrochemical measurements display that the as-cast Mg95.sGd3Zn1Zro.2 alloy with the continuous network eutectic phase exhibits the greatest corrosion resistance, while T6 sample with some needle-like phases and the particle phases is the worst among the three alloys. It is proposed to be mainly related to the amount, composition, microstructure and distribution of the precipitated phases.

Microstructure and mechanical behavior of Mg-5Zn matrix influenced by particle deformation zone

The effect of particle deformation zone(PDZ) on the microstructure and mechanical properties of SiC_(p)/Mg-5Zn composites was studied.Meanwhile,the work hardening and so ftening behavior of SiC_(p)/Mg-5Zn composites influenced by PDZ size were analyzed and discussed using neutron diffraction under in-situ tensile deformation.The evolution of FWHM(full width at half maximum) extracted from the diffraction pattern of SiC_(p)/Mg-5Zn composites was used to interpret the modification of dislocation density during in-situ tension,which discovered the effect of dislocation on the work hardening behavior of SiC_(p)/Mg-5Zn composites.In addition,the tensile stress reduction(△P_i) values during in-situ tension test were calculated to analyze the effect of PDZ size on the softening behavior of SiC_(p)/Mg-5Zn composites.The results show that the work hardening rate of SiC_(p)/Mg-5Zn composites increased with the enlargement of PDZ size,which was attributed to the grain size of SiC_(p)/Mg-5Zn composites increased with the enlargement of PDZ size.Moreover,the stress reduction(△P_i) values increased continuously during in-situ tensile for SiC_(p)/Mg-5Zn composites due to the increased stored energy produced during plastic deformation,which provided a driving force for the softening effect.However,the effect of grain size on the softening behavior is greater than that of the stored energy,which led to the tensile stress reduction(△P_i) values of P30(d_(PDZ)=30 μm)-SiC_(p)/Mg-5Zn composite were higher than that of P60(d_(PDZ)=60 μm)-SiC_(p)/Mg-5Zn composite when the ε_(ri) were 0.25,0.5,0.75 and 1,respectively.

Microstructure, Tensile Properties and Work Hardening Behavior of an Extruded Mg–Zn–Ca–Mn Magnesium Alloy

A new Mg-2.2 wt% Zn alloy containing 1.8 wt% Ca and 0.5 wt% Mn has been developed and subjected to extrusion under different extrusion parameters.The finest(~0.48 μm) recrystallized grain structures,containing both nano-sized MgZn2 precipitates and α-Mn nanoparticles,were obtained in the alloy extruded at 270℃/0.01 mm s-1.In this alloy,the deformed coarse-grain region possessed a much stronger texture intensity(~32.49 mud) relative to the recrystallized fine-grain region(~13.99 mud).A positive work hardening rate in the third stage of work hardening curve was also evident in the alloy extruded at 270℃,which was related to the sharp basal texture and which provided insufficient active slip systems.The high work hardening rate in the fourth stage contributed to the high ductility extruded at 270℃/1 mm s-1.This alloy exhibited a weak texture,and the examination of fracture surface revealed highly dimpled surfaces.The optimum tensile strength was achieved in the alloy extruded at 270℃/0.01 mm s-1,and the yield strength,ultimate tensile strength and elongation to failure were^364.1 MPa,~394.5 MPa and^7.2%,respectively.Fine grain strengthening from the recrystallized fine-grain region played the greatest role in the strength increment of this alloy compared with Orowan strengthening and dislocation strengthening in the deformed coarse-grain regions.

Effect of Extrusion Temperature on the Microstructure and Mechanical Properties of Mg–5Al–2Ca Alloy

In this work, the Mg–5Al–2Ca alloy was extruded at 573, 623 and 673 K, with a ratio of 16：1 and a constant speed of 3 mm/s. Results demonstrate that the Al2Ca particle is formed in Mg–5Al–2Ca alloy. The size, amount and distribution of Al2Ca particles are influenced evidently by extrusion temperature. Unlike previous reports, the intensity of basal texture increases with increasing extrusion temperature, and the reasons are analyzed and given. Even though the average grain size increases as the extrusion temperature increased from 573 to 623 K, the YS, UTS and elongation of asextruded Mg–5Al–2Ca alloy are almost kept the same at 573 and 623 K. The reason is speculated as the balance of grain size, Al2Ca phase and texture at the two temperatures. The work hardening rate depends on extrusion temperature, and the largest θ value of Mg–5Al–2Ca alloy is obtained when the extrusion was performed at 623 K.

Microstructure and Corrosion Behavior of the As-Extruded Mg-4Zn-2Gd-0.5Ca Alloy

In order to study the corrosion resistance of extruded magnesium alloys,the Mg-4Zn-2Gd-0.5Ca alloy was extruded at the speed of 0.01-0.1 mm/s with the temperature of 280-360℃in present study.Hot extrusion results show that the volume fraction of precipitates(Vpre),VDRX(the dynamic recrystallization rate) and the average size of DRXed grain(dDRX) decrease with the decrease in extrusion speed,and the corrosion rate of the alloy also shows a downward trend.On the contrary,the values of Vpre,VDRX and dDRX increase with the increase in extrusion temperature,and the corrosion resistance of Mg-4Zn-2Gd-0.5Ca alloy decreases.When the extrusion speed is 0.01 mm/s and the extrusion temperature is 280℃,the alloy has the best corrosion resistance.The corrosion of extruded Mg-4Zn-2Gd-0.5Ca alloy occurs preferentially on the magnesium matrix around W and I phases in the DRXed zone.With the further corrosion,the corrosion continues to spread along the phase,and the corrosion area gradually increases.Galvanic corrosion plays a leading role in the corrosion process.Moreover,there are a large number of basal plane textures in the unDRXed region,which is conducive to improving the corrosion resistance of magnesium alloys.In addition,the decrease in grain size also makes the corrosion of magnesium alloy more uniform.