The Effect Of TiC-TiB₂ Particles On Microstructure And Mechanical Properties Of Twin Roll Cast Al-Mn-Si Alloy

The TRC process to produce aluminum alloy strips has the advantages of short process,low energy consumption,low investment cost,and high degree of automation.However,due to its unique production process,TRC strips have serious center segregation and uneven microstructure,which severely restricts its application in the field of high-end aluminum sheet.Therefore,this paper took Al-Mn-Si alloy as the research object and introduced TiC-TiB₂ particles to refine the grains,enhanced the uniformity of the microstructure,and eliminated center segregation.In order to further increase the solubility of Mn,Fe and other alloying elements,promote the precipitation of Mn during annealing,and obtain a high volume fraction,small size,and uniformly distributed dispersoids,so as to control the microstructure of grains after annealing and improve the mechanical properties of Al-Mn-Si alloy.The main research conclusions of this paper are as follows:(1)TiC-TiB₂ particles significantly refined the grains,and the refining effect on the surface grains was much greater than the center grains.The grains of the TRC Al-Mn-Si alloy were characterized by a coarse surface layer and a small center.After adding TiC-TiB₂ particles,the grain size distribution became uniform,and the average size gap between the surface layer and the center grain decreased.(2)TiC-TiB₂ particles can eliminate the center segregation,affect phase selection,and promote the solution of Mn.The TRC Al-Mn-Si alloy formed center segregation dominated by?-Al(Mn,Fe)Si and Si,and the blank sample had a higher content of?-Al(Mn,Fe)Si.After adding TiC-TiB₂ particles,?-Al grains nucleated and split the aluminum melt,reduced the content of Mn and Si elements in the aluminum liquid at the center,and the eutectic reaction shifted to form a uniformly dispersed eutectic microstructure dominated by Si,and reduced the proportion of?-Al(Mn,Fe)Si.(3)TiC-TiB₂ particles can refine the size of the dispersoids,increase its volume fraction,enhance the uniformity of its distribution,and inhibit the coarsening of the dispersoids after long-term annealing.After adding 0.6 wt%TiC-TiB₂ particles and annealing at 400°C for 24 h,the volume fraction of the dispersoids of the thin plate increased by 0.04%,and the average size of the dispersoids was refined by 9.9%.The volume fraction of the dispersoids of the thick plate was increased by 0.78%,and the average size of the dispersoids was refined by 32.5%.The distribution of the dispersoids of the blank sample showed the characteristics of fine surface layer and sparse center.After adding TiC-TiB₂ particles,the difference in the number density of the surface layer and the center dispersoids were significantly reduced.(4)TiC-TiB₂ particles promoted the recrystallization of TRC Al-Mn-Si alloy,and improved the uniformity of the recrystallized microstructure.The center of TRC strips contained coarse second-phase particles(>1?m),which could induce recrystallization and nucleation.The number density of the center dispersoids was less than the surface layer,and the pinning effect on dislocations and subgrain boundaries movement was weaker.In the recrystallization annealing process,the center always recrystallized first,and the center grain size was larger than the surface layer.(5)After adding TiC-TiB₂ particles,the mechanical properties of TRC Al-Mn-Si alloy were improved.The tensile results at room temperature showed that after adding TiC-TiB₂ particles,the yield strength of the sheet increased from 119.6 MPa to 141.3MPa,and the uniform elongation increased from 4.1%to 5.4%.The yield strength of the thick plate increased from 79.0 MPa to 92.9 MPa,and the uniform elongation increased from 7.2%to 10.1%.The high temperature tensile results showed that after adding TiC-TiB₂ particles,the yield strength of the thin plate increased from 59.7MPa to 65.1 MPa,and the yield strength of the thick plate increased from 51.7 MPa to63.9 MPa,with an increase of 9.0% and 23.6%,respectively.