Study On Microstructure And Properties Control Of Al-3Mg-0.5Mn Alloy

The high-throughput continuous casting and rolling process is a new and efficient aluminum alloy sheet and strip production process.Compared with the open billet hot rolling method,the production process has low energy consumption,short process,high efficiency and low cost.5xxx series aluminum alloy has the advantages of high specific strength,easy processing and forming,good corrosion resistance and good welding performance.It is an ideal material in the automotive industry.Mg is the main alloying element of 5xxx series aluminum alloys,and it mainly plays the role of solid solution strengthening in the alloy.However,when the magnesium content is high,the crystallization temperature interval is large,the fluidity is poor,and structural defects such as segregation and inclusions are easy to occur,which is not suitable for high-throughput continuous casting and rolling process.In this paper,the composition of Al-3Mg-0.5Mn alloy was designed by microalloying,using DSC,OM,SEM,EDS,XRD,EBSD,microhardness and tensile test,electrochemical analysis,nitric acid mass loss test and peeling corrosion tests were conducted to study the influence of alloying elements Er,Zr,Cu,Si and Zn on the crystallization temperature interval,structure,mechanical properties and corrosion properties of Al-3Mg-0.5Mn alloy.The effect mechanism of the second phase particles formed by adding trace elements on the tensile strength and corrosion resistance of cold-rolled alloys was investigated.The research results of the as-cast and homogenized microstructures and properties of the experimental alloy showed that the grain structure of as-cast alloys was refined by the addition of trace Zr,Si,Cu elements,the most obvious of which was the refinement effect of Si.The addition of trace Er and Zn elements did not make the grain of as-cast alloy obviously refined,but the dendritic substructure inside the alloy was refined.The homogenization effect of Al-3Mg-0.5Mn-0.2Er alloy and Al-3Mg-0.5Mn-0.2Zn alloy were not ideal after homogenization annealing of 460?×24 h,and there were still more eutectic phase residues.The homogenization effect of Al-3Mg-0.5Mn alloy,Al-3Mg-0.5Mn-0.2Zr alloy,Al-3Mg-0.5Mn-0.2Cu alloy and Al-3Mg-0.5Mn-0.2Si alloy were more obvious,and a large number of dendritic segregation in the as-cast structure was dissolved into the matrix.In addition to the matrix phase Al,the phase composition of the as-cast and homogenized alloys mainly contained Al₃Mg₂ phase and Al₆?Fe,Mn?phase.The addition of trace elements formed second phases such as Al₃Er,Al₃Zr,Al₂Cu Mg,Mg₂Si,Mg Zn₂,and Mg₃₂?Al,Zn?₄₉.After the as-cast alloy was homogenized and annealed,the non-equilibrium second phase was partially dissolved in the aluminum matrix,and the Al₃Mg₂ phase was precipitated in large amounts after the homogenized and annealed.The results of studies on the microstructure and mechanical properties of cold-rolled alloys showed that the microstructure of the alloy was significantly fibrous after cold rolling.The addition of Er?Zr?Cu?Si and Zn elements made the fibrous structure refined to varying degrees.After cold rolling,the grains of the alloy were severely elongated,cracked and distributed fibrously along the rolling direction,and a large number of fine grains were sandwiched between the fibrous structures.The grain types were mainly deformed grains with a small angle grain boundary?greater than 90%?,and there were some deformed substructures and a small amount of recrystallized grains.The cold-rolled alloy mainly contained S texture,Copper texture,Brass texture,and Goss texture.Among them,the S texture content was the highest.The addition of alloying elements increased the content of deformed texture.The addition of trace elements Er,Zr,Cu,Si and Zn all improved the tensile strength and yield strength of Al-3Mg-0.5Mn alloy.Among them,the strength of Cu-containing alloys increased most significantly,followed by Zr-containing alloys.The tensile strength was increased by 31 MPa and 27 MPa,and the yield strength was increased by 34 MPa and 27 MPa,respectively.The strengthening mechanism of the alloy containing Er and Zn elements was mainly the second phase strengthening,and the strengthening mechanism of the alloy containing Zr,Cu and Si elements was mainly the fine grain strengthening and the second phase strengthening.The results of research on the corrosion resistance of cold rolled alloys showed that in addition to the element Si,after the addition of elements Er,Zr,Cu,and Zn,the self-corrosion potential of the Al-3Mg-0.5Mn alloy increased,the corrosion current density decreased,and the corrosion resistance was improved.The addition of trace elements had little effect on the intergranular corrosion resistance of the alloy,and the mass loss was in the range of 1 mg/cm²?2 mg/cm²,which belonged to the intergranular corrosion resistant alloy.The exfoliation corrosion grades of cold-rolled alloys were all P grades,indicating that it had no exfoliation corrosion and had good spalling corrosion resistance.Through the comparative analysis of the results,it was found that compared with the Al-3Mg-0.5Mn alloy,the Crystallization temperature interval of Al-3Mg-0.5Mn-0.2Zn alloy was reduced by 4.7°C,and the crystallization temperature interval was only17.8°C.This was because the addition of Zn formed Mg Zn₂ and Mg₃₂?Al,Zn?₄₉ phases and consumed a certain amount of Mg elements,resulting in a reduction in the crystallization temperature interval of the alloy.The alloy had good mechanical properties and corrosion resistance,and good overall performance.