Microstructure And Mechanical Properties Of Al-3Li-1Cu-0.2Er-0.1Zr Alloy By Large Strain Rolling

Although Al₃Li phase is one of the main strengthening phases in Al-Li alloy,the existence of Al₃Li phase can easily cause the planar slip during deformation,triggering the poor plasticity and toughness of Al-Li alloys.Considering the issue,through introducing core-shell composite phase and processing the alloy by large strain rolling(LSR),this thesis optimized the microstructure and mechanical properties of Al-3Li-1Cu-02Er-01Zr(wt.%)alloy with high Li content.Specifically,The correlation among rolling process,microstructure and mechanical properties of Al-3Li-1Cu-02Er-01Zr alloy was researched.Furthermore,the rolling process parameters(rolling temperature and strain)were optimized.The results are describle as follows.The as-cast,homogenized and LSRed Al-3Li-1Cu-02Er-01Zr alloy were characterized by OM,XRD,SEM,EDS and TEM.The results show that(Cu and Er)-rich phases continuously distribute along the grain boundaries of as-cast Al-3Li-1Cu-0.2Er-0.1Zr alloy.After homogenization,some of the continuous(Cu and Er)-rich phases along grain boundaries are dissoluted.After rolling at 500°C,the continuous(Cu and Er)-rich phases are broken and homogeneously distribute in the?-Al matrix.At the same time,a large number of nano-Al₃Li,nano-Al₃(Er,Zr)and nano-Al₃(Er,Zr,Li)phases are precipitated.Comparing the microstructure characteristics of as-rolled Al-3Li-1Cu-0.2Er-0.1Zr alloy under different strains at 500°C,the dynamic recrystallization doesn't occur in the strain of 66.7%.However,the obvious dynamic recrystallization occurs in the strains of 75%and 83.3%.The relatively complete recrystallization can be achieved when the strain is 75%.However,the heterogeneous plastic deformation commences with the continuous increase of strain to83.3%:the recrystallization occurs in partial grains,and the rest is the deformation structure without recrystallization.Comparing the microstructure evolution at 400°C,450°C and500°C under the strain of 75%,the as-rolled Al-3Li-1Cu-0.2Er-0.1Zr alloy at 450°C has a relatively complete dynamic recrystallization,and the grain size is significantly refined to about 0.9?m by recrystallization.On the basis of the LSRed Al-3Li-1Cu-0.2Er-0.1Zr alloy at450°C with the strain of 75%,the alloy is cold rolled at room temperature with different reduction.After 20%cold rolling,the grain size is further refined,and the dislocations are introduced into the recrystallized grains.The tensile testing results show that the strength and elongation of Al-3Li-1Cu-0.2Er-0.1Zr alloy can be significantly improved after LSR.The alloy possesses the excellent strength(YS=252 MPa and UTS=348 MPa)and ductility(EL=19.1%)after rolling at 450°C with the strain of 75%.The YS of the alloy is further improved by cold rolling with 20%and 50%reduction,but the elongation decreases significantly.The YS and UTS of the alloy after 20%rolling reduction at room temperature are improved to 340 MPa and 386 MPa,respectively,and the elongation decreases to 7.9%.After 50%reduction rolling,the YS and UTS are improved to 363 MPa and 404 MPa,respectively,but the elongation decreases to 2.4%.Al-3Li-1Cu-0.2Er-0.1Zr alloy exhibits excellent mechanical properties after LSR rolling at 450°C with the strain of 75%.This can be attributed to the relatively complete recrystallization,the refined grains,and nano-Al₃Li,nano-Al₃(Er,Zr)phases.After the subsequent cold rolling at room temperature with 20%reduction,the YS of the alloy is furter improved,but the elongation is decreased,which can be ascribed to the increase of dislocation in the recrystallized grains,and the grain size refinement.