Study On Microstructure And Properties Of AlLiMgScTi System Lightweight High Entropy Alloys Prepared By Mechanical Alloying

High entropy alloys are a brand-new type of multi-principal component alloys developed during the exploration of new alloy design concepts.Under the interaction of multi-principal elements,they generally feature a simple solid solution phase structure and attractive performances superior to most traditional alloys,implicating great application prospect.Among them,lightweight high entropy alloys are a new kind of high entropy alloy system developed from the lightweight design of traditional high-entropy alloy systems,aim to obtain a new type of lightweight alloy materials with both low density and outstanding properties,and have become a research hotspot in high entropy alloy materials area at present.In this paper,based on the reported lightweight high entropy alloys,the phase formation rule for lightweight high entropy alloys were frist discussed.Besides,(AlLiMg_0.5Ti_1.5)_100-XScx（x=0,5,10,15,20）lightweight high entropy alloy system were prepared by mechanical alloying（MA）and cold-press sintering（CPS）.The effects of different contents of Sc and sintering temperature on microstructure and mechanical properties of(AlLiMg_0.5Ti_1.5)_100-XScx（x=0,5,10,15,20）lightweight high entropy alloys were studied.Furthermore,the effects of Zn,Zr and V and sintering temperature on the microstructure and mechanical properties of AlLiMgScTiM（M=Zn,Zr,V）lightweight high entropy alloy system were studied.The main conclusions can be drawn as follows:（1）For the as-cast type-I lightweight high entropy alloys,WhenΩ≥1.1 andδ≤6.0%or-17 k J/mol≤≤-10 k J/mol,as well asδ≤6.0%,the alloys tend to form a simple solid solution phase structure.As for the as-cast type-II lightweight high entropy alloys,the solid-solution phases and intermetallic phases will form at 3.0%<δ<6.6%and the intermetallic phases form at 6.6%＜δ<14.0%,while the amorphous phases atδ>14%.（2）For the as-milled AlLiMgScTiScx system lightweight high entropy alloys,simple solid-solution phase structures were generally formed.Among them,single HCP solid-solution phase was formed in the(AlLiMg_0.5Ti_1.5)_100-XScx（x=5,10,15,20）system alloy.Moreover,the main HCP phase and traced AlLiphase,the main HCP phase and an unknown phase,the dual-phased HCP（HCP1+HCP2）,as well as the single-phased BCC structure was formed in the Al₂₅Li₂₅Mg_12.5Ti_37.5,Al₂₀Li₂₀Mg₁₀Ti₄₀Zn₁₀,Al₂₀Li₂₀Mg₁₀Zr₂₀Ti₃₀ and Al₂₀Li₂₀Mg₁₀V₂₀Ti₃₀,respectively.（3）Compared with the as-milled AlLiMgScTiScx system lightweight high-entropy alloys,the as-sintered alloys generally possess the more complex microstructures.Among them,Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ alloy sintered at 550℃ has the simplest microstructure,consisting of the main HCP solid-solution phase and a small amount ofγ-Al₁₂Mg₁₇ phase.In addition,except that Al₂₀Li₂₀Mg₁₀Zr₂₀Ti₃₀ alloy is composed of two-phased HCP（HCP1+HCP2）solid solution phases and a small amount of unknown phase after sintering at 650℃ and 750℃,the effect of sintering temperature on the microstructure of other light high entropy AlLiMgScTiScx alloy is generally significant.（4）With the increase of the sintering temperature,the microhardness of AlLiMgScTiScx system lightweight high entropy alloys are all on the obvious increase.In the(AlLiMg_0.5Ti_1.5)_100-XScx（x=0,5,10,15,20）system lightweight high entropy alloys,as the Sc content increases,the microhardness of the alloys present to keep on monotonously incremetal trend.Among them,Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ sintered at 650℃ has a hardness of up to 589 HV.Besides,Among the AlLiMgScTiM（M=Zn,Zr,V）system lightweight high-entropy alloy,Al₂₀Li₂₀Mg₁₀V₂₀Ti₃₀ sintered at 750℃ has the highest hardness value in the whole studied AlLiMgScTiScx alloy system,reaching 595HV.（5）Overall,in the AlLiMgScTiScx system lightweight high-entropy alloys,the three alloys,Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ sintered at 550℃,Al₂₀Li₂₀Mg₁₀V₂₀Ti₃₀ sintered at 650℃,and Al₂₀Li₂₀Mg₁₀Zr₂₀Ti₃₀ sintered at 750℃,not only formed simple microstructure dominated by HCP,HCP+BCC and HCP1+HCP2 solid-solution phases,respectively,but also have mechanical properties that are better than commonly used Ti64 light alloys,and their microhardness values are 379 HV,446 HV and 425 HV,respectively.