Effects Of Mn Microalloying And Heat Treatment On Microstructure And Properties Of 6061 Aluminum Alloy

As one of the most important alloys of Al-Mg-Si series aluminum alloys,6061 aluminum alloy is widely used in mechanical parts,structural engineering,modern construction,transportation and other fields.The application of industrial 6061 aluminum alloy in some special fields is also limited by its own strength.The current research is mainly to increase the comprehensive mechanical properties of aluminum alloys of 6xxx by adding new components?Mn,Cr,etc.?to the as-cast alloy or using new processing techniques.In this paper,the single-roll melt rotation cooling method is used to rapidly cool the molten Al6061-0.22wt.%Mn and Al6061 alloys,so that the Mn element is fully dissolved in the alloy matrix,overcoming the limitations of the Mn content in the as-cast state and obtaining ultrafine crystal Aluminum alloy strips which can be hot extruded to produce rods.Metallography,X-ray diffraction,scanning electron microscopy,transmission electron microscopy,backscattered electron diffraction,energy spectrum and density,hardness,tensile test and other test methods were used to study and compare the microstructure and mechanical properties of aluminum alloy thin strips and hot extruded rods and explore the heat treatment process of aluminum alloy.The conclusion are as follows.?1?Under vacuum,after the rapid solidification treatment,Al6061-0.22 wt.% Mn alloy and Al6061 alloy form an ultra-fine grain aluminum alloy thin strip.The resulting aluminum alloy grains,with the average size of 2.1?m,are very fine and uniform in structure.The surface of the aluminum alloy strip near the copper wheel is tear-shaped and relatively smooth.The tissue is arranged in a layered arrangement along the direction of the linear speed of the copper wheel.While the particles away from the surface of copper wheel are observed basically equiaxed.Due to the rapid cooling rate,the solubility of alloy elements in the aluminum alloy matrix is increased,and the addition of trace Mn elements forms a greater supersaturation,resulting in an increase in the alloy's dissolution driving force,which further reduces the initial melting temperature.The rapid solidification process is a non-equilibrium solidification process,which makes the grains in a disordered orientation distribution state and the texture component is more complicated.In addition to the<111>and<001>orientations,there are?001?<100>,?-fiber and other textures,which have no preferred orientation.?2?The hot-extrusion process?460?,500?,530??is used to process the ultra-fine grain ribbon into bars that can be applied to structural parts.As the hot extrusion temperature increases,the structure of bars is gradually densificated and the grains are also gradually coarsened,which shows a mechanical properties rise and then a mechanical properties drop.The Al6061-0.22wt.%Mn alloy bar obtained the best mechanical properties under 500?extrusion process,which the tensile strength is up to 227 MPa and the total elongation remains above 20%.The addition of Mn element replaces part of the Fe in the?-Al Fe Si phase to form a dispersed?-Al₈?Fe Mn?₂Si,which transforms the?phase from a long needle to a group of?phase.At the same time,the properties of the Mn element and Fe element are similar so it can replace part of Fe and reduce the harmful effects of Fe.?3?To treat the Aluminium alloy bars?extrusion temperature 500??prepared by the hot stripping process by solution aging treatment,with the parameters of solution 535?×70 min+aging 175?×6 h.The tensile strength and yield strength of Al6061-0.22wt.%Mn alloy are 379MPa and 254 MPa,and the elongation after break is 14%.Compared with the Al6061 alloy,under the condition that the elongation after break is not much different from it,the tensile strength of Al6061-0.22wt.%Mn alloy increases by 30 MPa.The addition of trace Mn has little effect on the texture type and strength,but it significantly improves the type and distribution of the second phase.During the aging process,Al6061-0.22wt.%Mn alloy formed Mn-containing dispersed phase?-Al₁₅?Fe Mn?₃Si₂,which evenly distributed at the grain boundaries and sub-grain boundaries,hindered the migration and merge of the sub-grain boundaries and retained the extruded structure.At the same time,?-Al₁₅?Fe Mn?₃Si₂ can be used as a nucleation site for?"dispersion,which improves the peak hardness and yield strength of Al6061-0.22wt.%Mn.