Effect Of Temperature Controlled Rolling And Annealing On Microstructure And Properties Of Al-Mg-Si-Sc-Zr Alloy

Al-Sc alloy is a new generation of structural materials for aviation,aerospace and marine because of its high strength,high toughness,excellent weldability and corrosion resistance.In this article,Al-Sc alloy is prepared by melting.The change rule of microstructure and properties of Al-Sc alloy after room temperature rolling,liquid nitrogen control temperature rolling and liquid nitrogen control temperature rolling annealing treatment were systematically studied by metallographic microscope,scanning electron microscope,backscattered electron diffraction,X-ray diffractometry,transmission electron microscopy,hardness and tensile properties test.Firstly,Al-Mg-Si-Sc-Zr ingots were prepared by melting and casting.It was found that the internal elements and microstructures of ingots were unevenly distributed,and there were intragranular segregation and regional segregation.The average grain sizes of the alloy after as-cast and homogenization treatment has little change,which is118.9?m and 114.5?m,respectively.The hot working diagram of the alloy was established by hot compression test.The hot rolling temperature of the alloy was determined to be 460?,and the average grain size after hot rolling was reduced by 35%to 77.11?m,and Mg₂Si and Al₃(Sc,Zr)phases were precipitated during hot rolling.Second,the hot-rolled alloy was subjected to multi-pass rolling at room temperature and liquid nitrogen control temperature.The result shows that the hardness of both alloys after rolling is increased with the increase of deformation,but the hardness of alloy after room temperature rolling is 33%lower than that of liquid nitrogen control temperature rolling under the same amount of deformation.The tensile strength,yield strength and elongation of the two rolled alloys at 80%deformation were 443 MPa,415MPa,6.7%,and 335 MPa,296 MPa,and 5%,respectively.There are three main reasons for this performance difference.First,the alloy after liquid nitrogen control temperature rolling has high dislocation density and small grain size.Second,the influence of texture on mechanical properties after liquid nitrogen control temperature rolling is greater than that at room temperature rolling.Third,the Mg₂Si phase produced during hot rolling is peeled off and spheroidized at room temperature rolling,and finally all dissolved back into the matrix,so that the secondary phase in the alloy after room temperature rolling is dominated by Al₃(Sc,Zr)phase,and the alloy of liquid nitrogen control temperature rolling contains both two strengthening phase.Finally,in order to obtain the alloy with mixed grain structure,the plate with 80%deformation of liquid nitrogen control temperature rolling was isothermally annealed at200?,250?,300?and 350?,and the annealing time was 1 h.The result shows that the hardness,tensile strength and yield strength of the alloy decrease with the increase of annealing temperature,while the elongation increases.It is found that as the annealing temperature increases,the alloy recovers and the dislocation density decrease which is calculated by MWH method.When the temperature reaches 300?,recrystallization begins to occur.At 350°C,the degree of recrystallization further increases,and the internal recrystallized grains of the alloy accounted for 36.2%.