| Due to the good comprehensive performance,6xxx aluminum alloy has become the most important lightweight material for automobile body.However,compared with the traditional steel sheet for the automobile body,the 6xxx series aluminum alloy has problems such as low strength,poor formability and high cost,which seriously hinders the application and development of the 6xxx series aluminum alloy sheet for the automobile body.The conventional preparation process of the 6xxx series aluminum alloy includes direct chill casting,homogenization treatment,hot rolling,annealing,cold rolling,solution treatment,and pre-aging treatment.The homogenization treatment requires a high temperature of 500℃ or higher for about 24 h of heat preservation treatment,and the required cost is high,and the.spheroidization crystal phase during the homogenization process reduces the formability of the alloy sheet.Improve the homogenization treatment and explore the appropriate short-flow preparation process to effectively reduce costs.At the same time,microalloying is also an important means to improve the strength and formability of 6xxx series aluminum alloys.In this paper,the microstructure and properties of Al-0.36Mg-1.23Si aluminium alloy were characterized and analyzed by metallurgical microscope,scanning electron microscopy,transmission electron microscopy,X-ray diffraction and tensile tests.Firstly,the suitable short-flow preparation process was explored,and the influence of Zr and Zr and Sc compound addition on the microstructure and properties of the Al-0.36Mg-1.23Si alloy for the short-flow preparation was further studied.The short-flow preparation and microalloying studies provide basic data.The main findings are as follows:(1)Al-0.36Mg-1.23Si-0.11Zr alloy ingot has four kinds of heat treatment process before hot rolling(homogenization-free,300℃×8 h pre-treatment,540℃×24 h homogenization,300℃×8 h+540℃×24 h two-stage homogenization),then alloy plates are hot rolled,annealed,cold rolled and solidified by 545℃×30 min solution treatment and 17℃×7 min pre-aging treatment.The grain morphology has no obvious influence,and all of them are fine equiaxed crystals with a size of about 20 μm.The sheets with homogenization-free and 300℃×8 h pre-treatment,and then subjected to annealing,cold rolling,solution treatment and pre-aging treatment.The second phases are smaller,more numerous,and more distributed.(2)The best short-flow preparation process for Al-0.36Mg-1.23Si-0.11Zr alloy sheet for automobile body is:direct chill casting → hot rolling → 540℃×3 h annealling treatment with air cooling→cold rolling→ 545℃×30 min solution treatment with water quenching →170℃×7 min pre-aging treatment.After the best short-flow process,the performance indexes of the alloy sheet in the parallel rolling direction:yield strength was 142.8 MPa,tensile strength was 249.9 MPa,n10～20 value was 0.250,rio value was 0.842,the uniform elongation was 21.8%,the elongation at break was 29.1%,and the cupping value IE was 11.01 mm.After 2%pre-stretching and 170℃×30 min simulated paint baking treatment,the performance indexes:yield strength was 232.3 MP,tensile strength was 295.3 MPa,yield strength increments was 89.5 MPa,tensile strength increments was 45.4 MPa.(3)There were submicron AlFeSi and AlSiZrTi dispersoids in the matrix of Al-0.36Mg-1.23Si-(0～0.29)Zr alloy T4P sheet,and the grains were all equiaxed.With the increase of Zr content,the number of AlSiZrTi dispersoids increased significantly and the distribution was uneven,and there were densely distributed areas of banded dispersoids in the parallel rolling direction.Adding Zr can significantly refine the recrystallized grains of the alloy sheet after solution treatment at 545℃ for 30 min.As the Zr content increases,the recrystallized grain size decreases slightly(4)With the increase of Zr content,the strength of Al-0.36Mg-1.23Si-(0～0.29)Zr alloy T4P sheet increases first and then basically unchanged,and the value of n10～20 decreases first and then increases.Uniform elongation,elongation at break,rio value and cupping value IE gradually decreased.After 2%pre-stretching and 170℃×30 min,the sheet showed obvious baking hardening effect.When the Zr content is 0.15wt%,Al-0.36Mg-1.23Si alloy sheet has the best baking hardening effect.(5)With the increase of Sc content,the yield strength of the Al-0.36Mg-1.23Si-0.15Zr-(0～0.09)Sc alloy T4P sheet gradually decreased,and the tensile strength increases first and then decreases.The uniform elongation,n10～20 value and cupping value IE gradually increasing.The elongation at break and rio value have no obvious changes.After 2%pre-stretching and 170℃×30 min,the baking hardening effect of sheet gradually decreased.(6)The optimum Zr content in Al-0.36Mg-1.23Si alloy for automobile body is 0.15wt%.The average performance index of Al-0.36Mg-1.23Si-0.15Zr alloy T4P sheet prepared by the best short-flow preparation process:yield strength was 143.2 MPa,tensile strength was 252.0 MPa,the uniform elongation was 20.6%,the elongation at break was 27.3%,the 10～20 value was 0.247,the rio value was 0.577,the cupping value IE was 9.95 mm.After 2%pre-stretching and 170℃×30 min simulated paint baking treatment,the performance indexes:yield strength was 235.3 MPa,tensile strength was 296.4 MPa,yield strength increments was 96.3 MPa,tensile strength increments was 42.0 MPa. |
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