| According to actual production and application,improving the deep drawing performance of aluminum alloy sheets is the key to its wide application in automobile exterior bodies.The important factor affecting the stamping formability of the aluminum alloy sheet is the dispersoids with smaller size and higher density in the microstructure.At present,in the Al-1.3Si-0.42Mg alloy(the type of Al-Mg-Si),which is most promising in the field of automobile body panels,trace elements such as Cr are usually added to suppress recrystallization,and they will be dispersed with the form of precipitation in the process of ingot homogenization.Their configuration(including size,density and distribution)has an important influence on the strength,plasticity and stamp formability of the alloy sheet.In order to reveal the influence of Cr content(including the interaction of Mg,etc.)on its dispersoids,and effectively adjust the configuration of its dispersoids,in order to further improve the stamping formability.This paper systematically studies the effect of Cr on the microstructure and dispersoids of Al-1.3Si-0.42Mg with 0.2Cu(the type of Al-Mg-Si)aluminum alloy.It mainly uses OLYMPUS GX71 optical microscope,SSX-550 scanning electron microscope,field emission JEM2100F transmission electron microscope,AG-X100kN electronic universal material testing machine and other equipment for experimental research.Research indicates:(1)With the increase of Cr content,the dispersoids particles increase after the alloy semi-continuous ingot is processed by conventional homogenization,but the distribution is gradually uneven,especially when Cr increases to 0.4%,the precipitation free zone of dispersoids of the alloy increases significantly,and at the edge of precipitation free zone the particles of dispersoids are abnormally coarse and the size can reach 2 μm,but the dispersoids particles at the edge of the precipitation zone near the grain boundary are fine;when the Mg content increases from 0.42%to 1.2%,the number of dispersoids particles in the alloy increases.,but its distribution has no significant changes.(2)Adding a small amount of Cr(0.1%Cr),the Cr-containing dispersoids particles in the alloy are all crystal structures of α-Al15(MnFe)3Si2 phase with simple cubic structure,and the lattice constant is a=1.26 nm,even When the Mg content was increased to 1.2%,the crystal structure did not change.When the Cr content is increased to 0.4%,the dispersoids of the alloy becomes a dispersoids with Mn and Fe in the surface-centered cubic structure Al13Cr4Si4,and its lattice constant is a=1.09 nm;Mg can participate in the formation of the dispersoids,so it has the effect of promoting the increase and uniform distribution of the dispersoids particles.(3)Cr suppresses the recrystallization of the Al-1.3Si-0.42Mg alloy sheet during solution treatment.When the Cr content exceeds 0.2%,the partially elongated crystal grains in the alloy sheet are significantly increased,that is,the degree of insufficient recrystallization is increased;the Mg content increases,and the recrystallized grains refine.(4)Adding a small amount of Cr(0.1%)has the effect of increasing the yield and tensile strength of the alloy sheet.When the Cr content reaches 0.2%,the transverse strength of the alloy sheet is higher than that of the longitudinal direction,and an abnormal anisotropy appears.However,the longitudinal elongation is higher;when the Cr content reaches 0.4%,the strength of the alloy sheet is significantly reduced;when Cr is added at 0.1%and 0.2%,the strength of the alloy can be improved and at the same time a good elongation can be ensured.With the increase of Mg content(not more than 1.2%),the strength of the sheet increases.(5)With the increase of Cr content,the value of n15 of the alloy sheet increases monotonously,but the value of r15 and IE has the highest value and the lowest value when Cr is 0.2%;with the increase of Mg content,n15 is slightly reduced,r15 slightly elevated,while IE value slightly lower.Increasing the Mg content can significantly increase the thickness anisotropy index r15,and the effect on n15 is not significant,but it is not beneficial to the IE value.(6)Pre-ageing treatment of 170℃×8 min or 80℃×4 h immediately after solution hardening of the alloy sheet studied,can reduce the strength after natural aging,has little effect on elongation and r15,and slightly improve the effect of IE.The increase in Cr content has the effect of reducing the pre-ageing effect by n15.(7)Cr-containing of the Al-1.3Si-0.42Mg aluminum alloy semi-continuous ingot is pretreated at 250℃ before the conventional homogenization treatment,so that the number of dispersoids increases,the small-sized dispersoids grows,and the non-precipitation zone shrinks and distributes.More uniform,the Cr content increases the effect more obviously;the ingot is pretreated at 250℃ × 72h to make the size,quantity and distribution of the dispersoids particles of the alloy sheet in a better state,without significantly changing its strength,in the case of n15,r15 values and IE values,the elongation is significantly increased;when Cr is increased to 0.4%,the above effect is more pronounced. |
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