| With the development of aluminum radiators gradually reducing weight,miniaturization and high performance,the requirements for room temperature and medium and high temperature performance of Al-Mn alloys for radiators are also increasing.How to reduce the production cost based on further improving the mechanical properties and thermal stability of Al-Mn alloy has become a research hotspot in the field of current radiators.Alloying and suitable ingot heat treatment system are important ways to improve the structural stability and heat resistance of heat-resistant aluminum alloy.The Mg atoms dissolved in the matrix have a solid solution strengthening effect,while Fe and Si can promote the decomposition of the Mn-containing supersaturated solid solution,and promote the precipitation of a large amount of dispersed phase particles to cause dispersion strengthening.In this thesis,the microstructures of Fe and Si contents on Al-1.00Mn-0.85Mg-0.11Ni-(0.26?0.66)Fe-(0.16?0.87)Si alloy ingots,microstructures of alloy sheets,room temperature and high and medium temperature mechanical properties of alloy sheets are systematically studied.At the same time,the ingot heat treatment system before hot rolling(hot rolling after pretreatment at 375?×24 h,hot rolling after homogenization at 600?×24 h and direct hot rolling without homogenization)on Al-1.00Mn-0.85Mg-0.11Ni-(0.26?0.66)Fe-(0.16?0.87)Si alloy ingot,the microstructure of alloy sheet,room temperature mechanical properties and high temperature mechanical properties was stuied.Experimental data were provided for the development of new heat-resistant Al-Mn alloy sheets with low cost and excellent mechanical properties.The main conclusions obtained are as follows:(1)Al-1.00Mn-0.85Mg-0.11Ni-(0.26?0.66)Fe-(0.16?0.87)Si alloy ingot mainly consists of Al6(MnFe)phase?Al12(MnFe)3Si phase?Mg2Si phase?AlFeNi phase and AlMnFeSiNi phase.With the increase of Fe and Si content,the volume fraction of crystalline phase in the as-cast structure of the alloy gradually increased,and the as-cast grain of the alloy gradually refined.(2)Fe has a refinement effect on the grain of Al-1.00Mn-0.85Mg-0.33Si-0.1 1Ni-(0.26?0.66)Fe alloy annealed sheet.After homogenizing at 600?×24 h,the hot rolled sheet has fine equiaxed grains after annealing treatment,the grain size refined from 26 ?m to 19 ?m.The grain morphology of alloy annealing sheet prepared by after pretreatment at 375?×24 h hot rolling and direct hot rolling without homogenization is spheroid in longitudinal section,and the long axis of the ellipsoid along the rolling direction.The Fe content increased from 0.26%to 0.66%,and the long axis of the ellipsoidal grain was refined from 236 ?m and 190?mto 150 ?m and 109 ?m,respectively.(3)Si has no obvious effect on the grain size of the annealed sheet of Al-1.00Mn-0.85 Mg-0.65Fe-0.11Ni-(0.16?0.87)Si alloy.After homogenizing at 600?×24 h,the hot rolled sheet has fine equiaxed grains after annealing treatment,and the grain sizes range from 33 to 41 ?m.The grain morphology of alloy annealing sheet prepared by after pretreatment at 375?×24 h hot rolling and direct hot rolling without homogenization is spheroid in longitudinal section,and the long axis of the ellipsoid along the rolling direction.As the Si content increases from 0.16%to 0.87%,the long axis of the ellipsoidal grain is between 58?65 ?m and 55?63 ?m,respectively.(4)Room temperature performance of Al-1.00Mn-0.85Mg-0.11Ni-(0.26?0.66)Fe-(0.16?0.87)Si alloy annealed sheet is determined by grain boundary strengthening,solid solution strengthening of Mn and Mg atoms,and strengthening of second phase particles(AlMnSi dispersion phase+Mg2Si precipitated phase).As Fe content increased from 0.26%to 0.66%,solid solution strengthening weakened,grain boundary strengthening strengthened,and the strengthening of second phase particles increased first,then decreased,and then tended to be stable.As the Si content increased from 0.16%to 0.87%,the solid solution strengthening effect decreased gradually,while the strengthening effect of the second phase particles increased first and then tended to be stable.(5)With the increase of Fe content,the yield strength and tensile strength at room temperature of Al-1.00Mn-0.85Mg-0.11Ni-(0.26?0.66)Fe-(0.16?0.87)Si alloy annealed sheet increased first,then decreased,and then increased.The yield strength and tensile strength at room temperature decreased with the increase of Si content,while the increase of Fe and Si content had no obvious effect on the elongation of alloy sheet.The optimum content of Fe and Si in Al-1.00Mn-0.85Mg-0.11Ni-(0.26?0.66)Fe-(0.16?0.87)Si alloy sheet is 0.65%and 0.16%respectively.The corresponding optimal preparation process is:direct hot rolling without homogenization of the ingot,and the room temperature yield strength?tensile strength and elongation of the hot rolled sheet after annealing at 550?×1 h are 145 MPa?189 MPa and 23%.Its high-temperature yield strength?tensile strength and elongation at 200?300?exceed 53 MPa?60 MPa and 53%,respectively.(6)When the Al-1.02Mn-0.77Mg-0.11Ni-0.61Fe-0.16Si alloy sheet is thermally exposed at 200??250? and 300?,the thermal exposure time is extended from 24 h to 768 h,the size,number and morphology of excess crystalline phase particles and the dispersed phase particles in the alloy sheet did not change significantly.The number of particles in the precipitated phase of Mg2Si decreased first and then stabilized,and the grain size of the alloy sheet increased first and then stabilized.The room temperature yield strength and tensile strength of the alloy sheet have not changed significantly,but the elongation has decreased significantly.(7)When Al-1.02Mn-0.77Mg-0.11Ni-0.61Fe-0.16Si alloy annealed sheet is exposed to heat at 200?,the yield strength at 200? decreases gradually as the exposure time increases from 24 h to 768 h,and the tensile strength increases first and then decreases decreased slightly.When exposed to heat at 250?,with the heat exposure time extended from 24 h to 768 h,the high temperature yield strength,tensile strength and elongation of the alloy sheet at 250? increased first and then decreased.When exposed to 250? for 72 h,the high temperature mechanical properties of the alloy sheet are the best.Its high temperature yield strength?tensile strength and elongation are 68 MPa?99 MPa and 70%,respectively.When exposed to heat at 300?,the yield strength?tensile strength and elongation of the alloy sheet at 300? increased first and then decreased as the exposure time increased from 24 h to 768 h.When exposed to heat at 300? for 72 h,the alloy sheet had the best high-temperature mechanical properties,its high temperature yield strength,tensile strength and elongation are 60 MPa,68 MPa and 89%,respectively. |
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