Improvement of microstructure and mechanical properties of Al−Cu−Li−Mg−Zn alloys through water-cooling centrifugal casting technique

The microstructure and mechanical properties of as-cast Al−Cu−Li−Mg−Zn alloys fabricated by conventional gravity casting and centrifugal casting techniques combined with rapid solidification were investigated.Experimental results demonstrated that compared with the gravity casting technique,the water-cooling centrifugal casting technique significantly reduces porosity,refinesα(Al)grains and secondary phases,modifies the morphology of secondary phases,and mitigates both macro-and micro-segregation.These improvements arise from the synergistic effects of the vigorous backflow,centrifugal field,vibration and rapid solidification.Porosity and coarse plate-like Al13Fe4/Al7Cu2Fe phase result in the fracture before the gravity-cast alloy reaches the yield point.The centrifugal-cast alloy,however,exhibits an ultra-high yield strength of 292.0 MPa and a moderate elongation of 6.1%.This high yield strength is attributed to solid solution strengthening(SSS)of 225.3 MPa,and grain boundary strengthening(GBS)of 35.7 MPa.Li contributes the most to SSS with a scaling factor of 7.9 MPa·wt.%^(-1).The elongation of the centrifugal-cast alloy can be effectively enhanced by reducing the porosity and segregation behavior,refining the microstructure and changing the morphology of secondary phases.

Microstructure and mechanical properties of Mg,Ag and Zn multi-microalloyed Al-(3.2-3.8)Cu-(1.0-1.4)Li alloys

To develop super-high strength Al-Li alloy,the microstructures and mechanical properties of Mg,Ag and Zn microalloyed Al-（3.2-3.8）Cu-（1.0-1.4）Li alloys（mass fraction） with T8 temper were studied.The results showed that 1%of lower Li content restricted the strengthening effect of increasing Cu content,while simultaneous increase in Cu and Li contents contributed effectively to the enhancement of strength.The alloys were mainly strengthened by plenty of fine and well dispersed TI（Al2CuLi）precipitates.There were also some minor precipitates of θ＇（Al2Cu） and δ＇（Al3Li）,which became less in number density,even disappeared during the aging process.Meanwhile,higher Li content favored the formation θ＇ and δ＇ and a small amount of S＂（Al2CuMg） phases.In addition,strengthening effect and microstructure variation were analyzed through total non-solution mole fraction of Cu and Li and their mole ratio.To obtain Al-Li alloy with super-high strength,the total mole fractions of Cu and Li should be increased,and their mole ratios should also be kept at a certain high level.

Influence of Li addition on mechanical property and aging precipitation behavior of A1-3.5Cu-1.5Mg alloy

The influence of Li addition on mechanical property and aging precipitation behavior of Al-3.5Cu-1.5Mg alloy was investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM） and high resolution transmission electron microscopy（HRTEM）.The results show that the tensile strength can be significantly improved with the slightly decreased ductility and the form of fracture morphology is converted from ductile fracture into ductile/britde mixed fracture by adding 1.0%Li.Besides,the peak aging time at 185 ℃ is delayed from 12 to 24 h and the main precipitation phase S（Al2CuMg） is converted into S＇（Al2CuMg）＋δ（Al3Li）,while the formation of S＇（Al2CuMg） is delayed.

Microstructure evolution and mechanical properties of Al−3.6Cu−1Li alloy via cryorolling and aging

An Al−3.6Cu−1Li alloy was subjected to room temperature rolling and cryorolling to investigate their effects on microstructure evolution and mechanical properties.The microstructure and aging characteristics of the room temperature-rolled and the cryorolled alloys with 70%and 90%of thickness reductions were studied by microstructure analysis and mechanical tests.The samples subjected to cryorolling with 90%of thickness reduction have high strength and good toughness.This is mainly due to the inhibition of dynamic recovery and the accumulation of high-density dislocations in cryorolled samples.In addition,the artificial aging reveals that the temperature at which peak hardness is attained is inversely proportional to the deformation amount and directly proportional to the rolling temperature.Moreover,bright field images of cryorolled samples after aging indicate the existence of T1(Al2CuLi)precipitates.This suggests that the high stored strain energy enhances the aging kinetics of the alloy,which further promotes the nucleation of T1 phases.

Effects of Li content on microstructure and mechanical properties of as-cast Mg-xLi-3Al-2Zn-0.5Y alloys

The effects of Li content on the microstructure and mechanical properties of the as-cast Mg−xLi−3Al−2Zn−0.5Y(LAZx32-0.5Y)alloys were investigated by XRD,SEM,TEM,hardness tester and universal testing machine.The results show that the matrix of the alloy transforms fromα-Mg toα-Mg+β-Li and then toβ-Li when the Li content increases from 4%to 14%(mass fraction).All LAZx32-0.5Y alloys contain AlLi and Al_(2)Y,while MgLi_(2)Al appears only in the alloy containing theβ-Li matrix.As the Li content increases,the content of AlLi and MgLi_(2)Al gradually increases,while the content of Al_(2)Y does not change much.As the Li content increases from 4%to 10%,the ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually decrease while the elongation gradually increases.The corresponding fracture mechanism changes from cleavage fracture to quasi-cleavage fracture and then to microporous aggregation fracture.This is mainly attributed to the decrease ofα-Mg and the increase ofβ-Li in the alloy.When the Li content continues to increase to 10%and 14%,the yield strength,ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually increase,while the elongation decreases sharply,which is mainly attributed to the nano-scale MgLi_(2)Al uniformly distributed in theβ-Li matrix.

Microstructure and mechanical properties of as-cast and extruded Mg–8Li–3Al–0.7Si alloy

Mg–8Li–3Al–0.7Si alloy was prepared by casting and deformed by hot extrusion in this study.And the microstructure of as-cast and extruded specimens was analyzed with OM,XRD,SEM and EDS.Results show that the specimens are composed ofα-Mg,β-Li,AlLi,MgLiAl2 and Mg2Si phases.In as-extruded specimen,the microstructure is refined and theβ-Li phase has the effect of coordination during deformation.After hot extrusion,Chinese script Mg2Si phase is crushed into block-like and distributes uniformly in the matrix.Mechanical properties results show that the strength and elongation are both improved after hot extrusion.

Strengthening mechanism of T8-aged Al-Cu-Li alloy with increased pre-deformation

The microstructure evolution and mechanical properties of a T8-aged Al-Cu-Li alloy with increased pre-deformation(0-15%) were investigated,revealing the microstructure-strength relationship and the intrinsic strengthening mechanism.The results show that increasing the pre-deformation levels remarkably improves the strength of the alloy but deteriorates its ductility.Dislocations introduced by pre-deformation effectively suppress the formation of Guinier-Preston(GP) zones and provide more nucleation sites for T1 precipitates.This leads to more intensive and finer T1 precipitates in the samples with higher pre-deformation levels.Simultaneously,the enhanced precipitation of T1 precipitates and inhibited formation of GP zones cause the decreases in number and sizes of θ′ precipitates.The quantitative descriptions of the strength contributions from different strengthening mechanisms reveal that strengthening contributions from T1 and θ′ precipitates decrease with increasing pre-deformation.The reduced diameters of T1 precipitates are primarily responsible for their weakened strengthening effects.Therefore,the improved strength of the T8-aged Al-Cu-Li alloy is mainly attributed to the stronger strain hardening from the increased pre-deformation levels.

Effects of Li addition on microstructure and mechanical properties of Mg-6Al-2Sn-0.4Mn alloys

Effects of Li addition (2%, 5%, 8% and 11%) on microstructure and mechanical properties of the as-cast and as-extruded Mg?6Al?2Sn?0.4Mn-based alloys were investigated. Mg?xLi?6Al?2Sn?0.4Mn (x= 2, 5, 8 and 11, mass fraction, %) alloys were cast under an SF6 and CO2 atmosphere at 700 °C. After homogenization heat treatment at 350 °C, cast billets were extruded with a reduction ratio of 40:1 at 200 °C. Li addition to Mg?6Al?2Sn?0.4Mn resulted in the formation of MgSnLi2 and MgAlLi2 and/or AlLi intermetallic compounds and random basal texture. With increasing Li addition,β-Li phase was increased and the average area fraction of precipitates increased. Compression yield strength was increased from 212 to 235, 242 and 239 MPa as Li content was increased from 2% to 5%, 8% and 11%, respectively. Elongation was remarkably increased above 60% in 11% Li alloy. It is probable that Li-containing phases play a significant role in the enhanced mechanical properties by Li addition.

Engineering a flexible and mechanically strong composite electrolyte for solid-state lithium batteries

Lithium-ion batteries(LIBs)have greatly facilitated our daily lives since 1990s[1,2].To meet the ever-increasing demand on energy density,Li metal is seen as the ultimate anode because of its ultra-high specific capacity(3860 m Ah/g)and the lowest electrochemical potential(-3.04 V vs.the standard hydrogen electrode)[3–6].However,issues of Li metal anode,such as Li dendrite formation and large volume change during plating/stripping。

Evolution of Microstructure and Mechanical Property during Long-Term Aging in Udimet 720Li

Thermal stabilities of microstructure and mechanical property have been investigated on superalloy U720Li, which is of great interest of application for jet engine and land-based turbine disc. The results showed that, the primary and secondary gamma' particles maintain good thermal stability at 650 and 700 degreesC with aging time up to 3000 h, while the tertiary gamma' is apparently dependent on aging temperature and time. The tertiary gamma' particles undergo a procedure of coarsening, dissolution and eventually complete disappearance with the increasing of aging time and temperature. They exhibit unusual high sensibility upon aging temperature, which is attributed to the lattice misfit between the gamma' precipitates and the matrix in the alloy. The grain boundary phase M23C6 remains stable without forming of sigma phase even with aging time up to 3000 h at 700 degreesC. Microhardness decreases apparently with increasing aging time and aging temperature. Theoretical analysis based on dislocation mechanism indicates that the change of microhardness should be attributed to the evolution of the tertiary gamma' during aging.

Effect of Li addition on mechanical properties and ageing precipitation behavior of extruded Al-3.0 Mg-0.5 Si alloy

The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-resolution transmission electron microscopy(HRTEM)images.The results show that the tensile strength of the Li-containing alloy can be significantly improved;however,the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture.The elasticity modulus of the Li-containing alloy increases by 11.6%compared with the base alloy.The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si phase.The width of the precipitate-free zone(PFZ)of the Li-containing alloy is much wider at the over-ageing state than the base alloy,which has a negative impact on the ductile and results in the decrease of elongation.

Effect of heat treatments on microstructure and mechanical properties of sand cast Al−2Li−2Cu−0.5Mg−0.2Sc−0.2Zr alloy

This study focused on modifying heat treatment schemes to enhance the mechanical properties of sand cast Al−2Li−2Cu−0.5Mg−0.2Sc−0.2Zr alloy.Different three-stage solution treatment schemes((460℃,32 h)+(520℃,24 h)+(530/540/550℃,4/12/24/32 h))and aging temperatures(125,175,225℃)were designed for comparison.The microstructure evolutions were analyzed by optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results showed that the three-stage solution treatment of(460℃,32 h)+(520℃,24 h)+(530℃,12 h)could dissolve most of the secondary phases.The TEM results illustrated that fineδ'(Al_(3)Li)particles were homogeneously distributed in the matrix after aging at 175℃for 8 h,accompanied by a small amount of lath-shaped S′(Al_(2)CuMg)and plate-like T_(1)(Al_(2)CuLi)phases.The best comprehensive properties of yield strength of 376 MPa,ultimate tensile strength of 458 MPa and elongation of 4.1%were obtained by the optimal heat treatment scheme((460℃,32 h)+(520℃,24 h)+(530℃,12 h)+(175℃,8 h)).

Effect of Nd content on microstructure and mechanical properties of as-cast Mg-12Li-3Al alloy

In order to improve the mechanical properties of Mg-Li alloy with single β phase structure, Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) alloy was prepared. Subsequently, the as-cast microstructure and mechanical properties were observed and tested. The results showed that the structure of Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) as-cast alloy was composed of β phase matrix and Al_2Nd, Al_(11)Nd_3, MgLiAl_2, Al_4Li_9 and AlLi phases. With the increase of Nd content in the alloy, the Al-Nd intermetallic compounds have a trend to change from needle-like Al_(11)Nd_3 to granular Al_2Nd. The hardness of as-cast Mg-12Li-3Al-xNd(x=0.3, 0.7, 1.1, 2.0wt.%) alloy was stable at room temperature. The tensile strength of Mg-12Li-3Al-1.1Nd was as high as 180 MPa, the elongation rate of Mg-12Li-3Al-0.7Nd reached 53.7%, and the comprehensive mechanical properties of Mg-12Li-3Al-2.0Nd was the best. PLC phenomenon occurred during the tensile process of the alloys at room temperature. Therefore, the β-based Mg-Li alloy with good plasticity as well as enhanced strength can be obtained by a moderate addition of Nd and Al.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 8090 Al-Li ALLOY

The change of mechanical properties of the 8090 Al-Li alloy influenced by aging is attributed to the change of δ′-phase particle size and the precipitation of S′-phase.The δ′-phase may easily precipitate and rapidly grow,but the S′-phase can only precipitate with a longer stage of incubation.The precipitation of S′-phase would be promoted by cold working prior to ag- ing.The co-precipitation of δ′- and S′-phase could improve the strength and plastieity of the alloy,for which aging at 190℃.for 20—30 h seems to be optimal.In addition,the precipitate free zone( PFZ)can form at high angle grain boundary and its width is over 200 nm in peak aging condition.But at sub-grain boundary,the formation of PFZ is difficult.

Microstructure, cold rolling, heat treatment, and mechanical properties of Mg-Li alloys

The magnesium-lithium （Mg-Li） alloy exhibits two phase structures between 5.7wt% and 10.3wt% Li contents, consisting of the a （hcp） Mg-rich and the β （bcc） Li-rich phases, at room temperature. In the experiment, Mg-5Li-2Zn, Mg-9Li-2Zn, Mg-16Li-2Zn, Mg-22Li-2Zn, Mg-5Li-2Zn-2Ca, Mg-9Li-2Zn-2Ca, Mg-16Li-2Zn-2Ca, and Mg-22Li-2Zn-2Ca （wt%） were melted. During the melting process, the flux, which was composed of lithium chloride （LiCl） and lithium fluoride （LiF） in the proportion of 3：1 （mass ratio） and argon gas were used to protect the alloys from oxidation. The microstructure, mechanical properties, and cold-rolling workability of the wrought alloys were studied. The crystal grain of the alloys （adding Ga） is fine . The hardness of the studied alloys decreases with an increase in element Li. The density of the studied alloys is in the range of 1.187 to 1.617 g/cm^3. The reduction of the Mg-16Li-2Zn and Mg-22Li-2Zn alloys can exceed 85% at room temperature. The Mg-9Li-2Zn-2Ca alloy was heat treated at 300℃ for 8, 12, 16, and 24 h, respectively. The optimum heat treatment of the Mg-9Li-2Zn-2Ca alloy is 300℃×12h by metallographic observation and by studying the mechanical properties of the alloys.

Comparative Study on the Microstructure and Mechanical Properties of Mg-Li-Al Based Alloys with Yttrium and Strontium Addition

The effects of yttrium and strontium on the microstructure and mechanical properties of Mg- 11Li-3A1 magnesium alloy （LA113） are compared and analyzed. Microstructures and phases of the alloys were studied with optical microscope （OM）, scanning electron microscope （SEM）, X-ray diffractometer （XRD） and energy dispersive spectrometer （EDS）. Mechanical properties of alloys were measured with tensile tester. The results show that yttrium and/or strontium additions produce a strong grain refining effect in LA113 alloy. AI2Y and AI4Sr, etc. phases with different morphologies are verified and exist inside the grain or at the grain boundaries, which directly impact on the mechanical properties of LA113 alloy. The results of tensile tests show that, the as-extruded LA113-1Y-1 Sr alloy obtains the optimal tensile property of which the tensile strength and elongation are 253.56 MPa and 18.12%, the tensile strength is increased by almost 25% compared with the as- extruded LA113 alloy.

Microstructure and mechanical properties of Mg-xLi-3Al-1Ce alloys

Several Mg-xLi-3Al-1Ce alloys were prepared by vacuum induction heating. These alloys are Mg-5Li-3Al-1Ce,Mg-8Li-3Al-1Ce and Mg-14Li-3Al-1Ce,respectively. The microstructure and phase composition of these alloys were analyzed by optical microscopy,scanning electron microscopy,energy dispersive X-ray spectroscopy and X-ray diffractometry. The mechanical properties of these alloys were measured with tensile tester. The results show that,Mg-5Li-3Al-1Ce has a single phase(α) structure,Mg-8Li-3Al-1Ce has a double phases(α+β) structure,Mg-14Li-3Al-1Ce has a single phase(β) structure. And some compounds distribute in the matrix. After being rolled,the grain size of all the alloys is refined. Under the condition of the same content of other alloying elements,the mechanical properties of Mg-5Li-3Al-1Ce are relatively high. With increasing Li content,the strength of both as-cast and as-rolled alloy decrease. For the as-cast alloys,with increasing Li content,the elongation increases. While for the as-rolled alloys,with increasing Li content,the elongation decreases. Ce has refining effect on these alloys.

Influences of Misch Metal on Microstructure and Mechanical Properties of Mg-10Li-4Al Alloy

Mg-10Li-4Al and Mg-10Li-4Al-0.6RE alloys were prepared with vacuum induction melting method. The influence of RE on microstructure and mechanical properties was studied with SEM, XRD and tensile tester. The results showed that, the addition of RE made the α(Mg) phase disappeared and caused the formation of Al3La phase. And it improved both the tensile strength and elongation percentage of alloys.

Effect of aging on mechanical properties and localized corrosion behaviors of Al-Cu-Li alloy

The effects of aging on mechanical properties, intergranular corrosion and exfoliation corrosion behaviors of a 2197 type Al-Li alloy were investigated, and the mechanisms were studied through microstructure observation and electrochemical measurement of simulated bulk phase. The main strengthening precipitates of the alloy aged at 175 ℃ and 160 ℃ are δ′ and T1. T1 precipitation in the alloy aged at 160 ℃ is delayed, which results in its slower age strengthening and over-aging behavior than the alloy aged at 175 ℃. Meanwhile, aging temperature of 160 ℃ causes more uniform distribution and finer size of T1, resulting in its better strengthening effect. As aging time and aging temperature are increased, the size of T1 at grain boundaries and the width of PFZ along grain boundaries are increased, leading to an increase in the susceptibility to intergranular corrosion and exfoliation corrosion. It is suggested that better comprehensive properties can be obtained when the alloy is aged at 160 ℃.

Coupled Thermo-Mechanical Modeling of Long Cone-Shaped Forging Based on Rigid Visco-Plastic FEM

Based on synthetically considering the coupled thermo mechanical relations between temperature and deforming, a numerical simulation of the forging process for the special long cone shaped workpiece of Al 5.44Mg 2.15Li 0.12Zr alloy at high temperature was conducted by using the rigid visco plastic finite element method. The relations between the total load and the displacement during the forging, and the distributions of stress, strain, temperature and strain rate, which can provide useful information for the process design, are obtained.