Research On Microstructure,Properties And Superplasticity Of Al-3.25Mg-0.37Zr-0.28Mn-0.19Y Alloy

Aluminum-magnesium alloy is a common metal structural material,which has excellent corrosion resistance,welding performance and processing properties.It is widely used in aerospace,automotive transportation,3C products and other fields.The multi-directional forging process is a widely used severe plastic deformation process for preparing fine-grained materials,but there is little research on the process of multi-directional forging and warm rolling of Al-Mg alloys.In this paper,Al-3.25Mg-0.37Zr-0.28Mn-0.19Y alloy was used as the research object.The Al-Mg alloy sheets were fabricated by multi-directional forging and warm rolling,and the microstructure and mechanics of the specimens in different states during the preparation process were studied.Superplastic properties were analyzed and studied.The main research contents and results are as follows:(1)The multi-directional forging under stepwise decreasing temperature conditions was carried out.After the first pass,the grain refinement is the most remarkable,and the average grain size is 25.33 ?m.With the increase of pass number,the grain is gradually refined,and the average grain size of the ninth pass is refined to 16.44 ?m.Tensile properties and hardness of the specimens of the first,third,sixth and ninth pass were tested at room temperature,the tensile strength reached the maximum inthe sixth pass(?b=314.87 MPa),and the elongations of all passes were between 27.34%and 30.06%.The hardness reached a maximum of 97.23 HV in the ninth pass.(2)After warm rolling,the tensile strength reaches 354.67 MPa,and the hardnessis 113.66 HV,and the elongation is 18.47%.The tensile strength ofas-annealed specimen is 223.80 MPa,and the elongationis 41.94%.The strengthening effect of hot rolling and cold rolling is weaker than that of warm rolling.After warm rolling,the banded fibrous structure is formed,and the macroscopic texture is mainly strong {001}<110>texture and weak {112}<111>copper texture.Micro structure analysis and research were carried out by XRD,SEM and TEM analysis.Strength contribution of different strengthening mechanisms of the warmrolled specimen was estimated.The model of relationships between hardness and grain size and the model of relationships between strength and hardness were established.(3)High temperature tensile tests of Al-3.25Mg-0.37Zr-0.28Mn-0.19Y alloy under different deformation conditions of deformation temperatures of698?793 K and strain rates of5.0×10-4?1.67×10-2s-1 were carried out.When the deformation temperature is 793 K and the strain rate is 8.33×10-4 s-1,the maximum elongation is 412.5%.The micro structure changes,cavity changes and fracture morphologies of tensile specimens were analyzed during hot deformation.(4)The thermal deformation constitutive equation of modified Zerilli-Armstron and modified Johnson-Cook of the Al-3.25Mg-0.37Zr-0.28Mn-0.19Y alloy were constructed.The key parameters of superplasticity(stress exponent n,grain size exponent p and deformation activation energy Q)were determined,and the constitutive equation describing the mechanisms of superplastic deformation was established.