微量Ca添加对铸造Mg-Sm-Gd基合金显微组织与力学性能的影响

主要通过透射电子显微镜、高角度环形暗场扫描透射电子显微镜和拉伸测试研究微量Ca元素对Mg-Sm-Gd-Zn-Zr合金显微组织和力学性能的影响。结果表明,Mg-Sm-Gd-Zn-Zr合金中主要第二相为Zn元素富集的Mg_(3)RE相,Ca元素添加不仅可以细化晶粒,还可以促进Mg_(5)RE相和溶质原子富集的层错形成。此外,共格界面表明Mg_(3)RE相可以作为Mg_(5)RE相的形核位点,这些均有利于合金力学性能的提高。

Toward the development of Mg alloys with simultaneously improved strength and ductility by refining grain size via the deformation process

Magnesium(Mg) alloys, as the lightest metal engineering materials, have broad application prospects.However, the strength and ductility of traditional Mg alloys are still relativity low and difficult to improve simultaneously.Refining grain size via the deformation process based on the grain boundary strengthening and the transition of deformation mechanisms is one of the feasible strategies to prepare Mg alloys with high strength and high ductility.In this review, the effects of grain size on the strength and ductility of Mg alloys are summarized, and fine-grained Mg alloys with high strength and high ductility developed by various severe plastic deformation technologies and improved traditional deformation technologies are introduced.Although some achievements have been made, the effects of grain size on various Mg alloys are rarely discussed systematically and some key mechanisms are unclear or lack direct microscopic evidence.This review can be used as a reference for further development of high-performance fine-grained Mg alloys.

Recent advances of electromagnetic interference shielding Mg matrix materials and their processings:A review

In terms of lightweight electromagnetic interference(EMI)shielding structural materials,Mg matrix materials have proven to be the best,due to their exciting properties(e.g.low density,high specific strength,good electrical conductivity and excellent EMI shielding properties)and their wide range of applications in lightweighting in electronics,automotive and aerospace industries.Through processing,such as alloying,heat treatment,plastic deformation and composite processing,Mg matrix materials can be obtained with tailorable properties which can play a key role in designing materials for EMI shielding.This work introduces an overview of the research on the EMI shielding properties of Mg matrix materials as well as their EMI shielding mechanisms over the past few decades,focused on the influence of alloying,heat treatment,plastic deformation and composite processing for the EMI shielding properties of Mg matrix materials.At the end,conclusions and future perspectives are provided.

High specific strength MWCNTs/Mg-14Li-1Al composite prepared by electrophoretic deposition, friction stir processing and cold rolling

Multi-wall carbon nanotubes reinforced Mg-14Li-1Al composite(MWCNTs/Mg-14Li-1Al) was prepared by the processes of electrophoretic deposition, friction stir processing, and cold rolling. The microstructure and mechanical properties of the composite were investigated. The results show that, the microhardness of the composite is up to HV 84.4, which is 91.38% higher than that of the as-cast matrix alloy(HV 44.1). The yield strength and ultimate tensile strength of the composite are 259 and 313 MPa, which are 135.45% and 115.86% higher than those of the as-cast matrix alloy, respectively, and a high specific strength of 221.98 k N·m/kg is obtained. In the composite, the MWCNTs serve as nucleation particles during the friction stir processing and cold rolling, causing dynamic recrystallization and grain refinement. Furthermore, MWCNTs hinder the movement of dislocations and transfer the load from the matrix alloy, thus improving the strength.

Evolutions of Microstructure and Mechanical Properties in Mg-5Li-1Zn-0.5Ag-0.5Zr-xGd Alloy

The evolution of the microstructure and mechanical properties of alloy system with nominally composition Mg-5Li-1Zn-0.5Ag-0.5Zr-xGd(x=0,1.2,2.4,3.6,4.8,6)is evaluated based on computational phase diagram and corresponding experimental studies.The results show that grains are significantly refined with the increase of Gd content.The main phases of as-cast alloys areα-Mg,β-Li,AgLi_(2)Mg,and Mg_(3)Gd.With the increase of Gd content,the amounts of Mg_(3)Gd phase andβ-Li phase have been increased.When the Gd content exceeds 3.6 wt%,Mg_(3)Gd phase precipitates in a form of the network at the grain boundaries.The precipitation ofβ-Li can be attributed to the competitive dissolution of Zn,Gd,and Li in Mg.Meanwhile,γ″is formed after the addition of Gd,which grows and transforms intoγ′with the increase of Gd content.In solidification process,stacking faults are formed by solid transformation of partialα-Mg and Mg_(3)Gd.Eventually,with the synergistic effect of Mg_(3)Gd,β-Li,andγ″(orγ′),as the Gd content increasing,the tensile strength of the alloy first increases,then decreases,and the elongation decreases.When the content of Gd is 4.8 wt%,the ultimate tensile strength and yield strength reach the maximum values of 227 MPa and 139 MPa,and the elongation is 18.1%,respectively.

Microstructure Evolution of Extruded Mg-6Gd Alloy Under 175 ℃ and 150 MPa

The tensile creep behavior of extruded Mg-6 Gd alloy,having the tensile yield strength of～ 110 MPa at 175 ℃,has been investigated under 175 ℃ and 150 MPa. In this study, the extruded Mg-6 Gd sample exhibits the total tensile strain of ～10.5% after the creep time of 1100 h,and the fast plastic strain of ～4.6% at the beginning of the creep test. The microstructure result suggests that the dislocation deformation is the main deformation mode during creep, and the grains with orientation close to(0001) II ED disappear after creep. The creep process containing a low creep strain has no effective promotion for the precipitation compared with the aging process without strain. The origination of creep crack is related to the formation of precipitate-free zone during creep. The work offers an important implication to research the microstructure evolution under an applied stress in a weak aging response Mg alloy.

Microstructure and mechanical properties of high-strength high-pressure die-cast Mg–4Al–3La–1Ca–0.3Mn alloy

A new high-pressure die-cast(HPDC) Mg–4 Al–3 La–1 Ca–0.3 Mn(ALaX431) alloy with high strength has successfully been fabricated. This HPDC alloy in peakaged state exhibits tensile yield strength(TYS) of 220 MPa at room temperature and TYS of 145 MPa at 250 ℃,higher than the corresponding strength of HPDC Mg alloys reported so far. These high strengths are mainly due to the formation of fine grained structure, semi-continuous reticular structure consisting of stable Al_(3)La and(Mg,Al)2 Ca particles along grain boundaries and numerous nanoscale Al_(2)Ca precipitates within grains. Due to its higher strength than existing HPDC Mg alloys, the new developed alloy has great application potential.