Effects Of Heat Treatment Process On Microstructure And Properties Of The Extruded 6013 Aluminum Alloy

As a medium and high strength structural material,Al-Mg-Si-Cu aluminum alloy has been widely used in aerospace,rail transportation and mechanical electronic fields.The intergranular corrosion resistance of the alloy under traditional T6 state is difficult to meet the development needs of the existing industry.How to keep high strength of the alloy with excellent corrosion resistance has been the focus of research at home and abroad.This paper takes the extruded 6013 aluminum alloy as the research object,mainly adopted hardness test,electrical conductivity test,tensile test,intergranular corrosion,electrochemical corrosion,combined with scanning electron microscope（SEM）,transmission electron microscope（TEM）,DM 3.7 and other software systematically studied（1）the effects of hardness,electrical conductivity,mechanical properties and microstructure of the alloy during different solid solution temperatures and times and T6 aging,（2）the changes of microhardness,electrical conductivity,mechanical properties and corrosion behavior of the alloy by continuous heating aging,cooling aging and heating+cooling compound aging,（3）the evolution law of microstructure of the 6013 alloy under different non-isothermal aging processes.The main conclusions include:The residual Mg₂Si phase of the alloy decreased rapidly with the solid solution temperature increased,while the residual Al（FeMn）Si phase had no obvious change.HRTEM shows that the crystal structure of Al（FeMn）Si phase was FCC and the orientation relation with matrix was[043]_{Al（FeMn）Si}//[011]_Al.The better solid solution process was obtained at570℃for 30 min,and the hardness,electrical conductivity,tensile strength,yield strength and elongation of the alloy after T6 aging were 149 HV,42.7%IACS,406 MPa,380 MPa and 10.7%,respectively.when the final aging temperature of the continuous heating aging process increased from 140℃to 240℃at the same heating rate,the hardness and strength of the alloy increased firstly and then decreased,and the electrical conductivity increased continuously.When the temperature rose from 120℃to 220℃with 60℃/h,the tensile strength of the alloy was 399 MPa,reaching 98.3%of T6 state.However,the hardness,conductivity and elongation were 151 HV,44.6%IACS and 13.3%,respectively,which were significantly higher than those of T6 state.The aging time was only 1.7 h,accounting for 42.5%of T6 state,and the mechanical properties of the alloy under this aging process were similar to those of T6 state.The hardness and strength of the alloy during the continuous cooling aging increased firstly and then decreased sharply with the decrease of initial aging temperature at the same cooling rate.The electrical conductivity of the alloy decreased with the decrease of the initial aging temperature.When the alloy was cooled from 220℃to 120℃with a cooling rate of 40℃/h,the hardness,conductivity,tensile strength,yield strength and elongation of the alloy were 152 HV,46.6%IACS,407 MPa,383 MPa and 11.5%,respectively.The properties of the alloy were better than those of T6 state,shorting 37.5%of aging period than that of T6 state.For the heating+cooling compound aging with 120℃→220℃→180℃and 60℃/h,the hardness,electrical conductivity,tensile strength,yield strength and elongation of the alloy were 4%、10.3%、0.5%、1.3%and0.9%higher than those of T6 state,respectively,and the aging time was2.3 h,which was 42.5%shorter than that of T6 state.TEM and HRTEM analysis show that the G.P.ⅡZone was the main precipitated phases of the peak strength alloy.With the increase of final aging temperature,the precipitation sequence of 6013 alloy during the continuous heating aging was SSSS→G.P.I Zone→G.P.ⅡZone、L→Q’→Q,the size of precipitated phase in matrix increased,the precipitation spacing at grain boundary increased gradually,and the corresponding PFZ width widened gradually.The change of precipitates of the alloy during the continuous cooling aging was opposite to that during the continuous heating aging process.During the cooling aging process of the compound aging process,the density and size of precipitated phase in grain increased.For the heating+cooling compound aging with 120℃→220℃→180℃and 60℃/h,the distribution characteristic of intracrystalline precipitation of the alloy was similar to T6 state.The intergranular corrosion and electrochemical corrosion behavior show that the corrosion resistance of the continuous heating aged alloy increased with the increase of final aging temperature.The corrosion resistance of the continuous cooling aged alloy became weaker with the decrease of initial aging temperature.With the increase of the aging rate,the corrosion resistance of peak strength alloy increased firstly and then decreased.When the alloy was cooled from 220℃ to 120℃ with 40℃/h,the depth of intergranular corrosion was only 80.4μm and the I_corr was1.64×10^-6 A/cm²,the corresponding value of the alloy under T6 state were152.1μm and 7.11×10^-6 A/cm²,respectively.Non-isothermal aging could effectively improve the corrosion resistance of alloy.This thesis contains 57 pictures,19 tables and 110 references...