| 7005 aluminum alloy is a typical Al-Zn-Mg aluminum alloy,which has been used in aerospace,automobile transportation and other important national economic fields.In this paper,by optimizing the twostage homogenization,solid solution and aging heat treatment process of three phase,by means of metallographic microscope,scanning electron microscope(sem),transmission electron microscopy,universal material testing machine,electrochemical workstation on the microstructure of different heat treatment state,characterizing the mechanical properties and corrosion resistance,excellent comprehensive properties of 7005 aluminum alloy are obtained.The main research results are as follows:(1)The alloy was treated with three kinds of two-stage homogenization:350?/12h+470?/24h,410?/12h+470?/24h and 440?/12h+470?/24h.Among them,a large number of Al3Zr particles are precipitated in the samples at 440?/12h+470?/24h,and the distribution is fine and uniform,which can inhibit the growth of grain and realize fine grain strengthening,which is the best two-stage homogenization process.(2)The extruding alloy(extruding temperature 420?,extruding rate 1 mm/s)was treated with solid solution and water quenching.By comparing the 0-1008h natural aging hardness curves of the samples treated at 460?/2h and 475?/2h,the microhardness value of the samples treated at 475?/2h was higher(120HV).(3)Peak aging(T6:105 ?/24h),regression re-aging(RRA:105?/24h+200?/10 min+105?/24h)and four stage aging treatment(FSA:105?/24h+170?/100 min+Na/24h+90?/7h).The microstructure analysis and performance test show that the precipitates of T6 samples are mainly GP and ?'(MgZn2)phases,which have the highest strength,but the continuous MgZn2 phases are formed at the grain boundary,and the corrosion resistance of T6 samples is poor.In RRA state,the precipitates mainly consist of ?' phase and ? phase.The strength and elongation decrease,but the precipitates at the grain boundary are discontinuous.The precipitationfree zone at the grain boundary is wider and the corrosion resistance is better.However,FSA samples are composed of GP and ?' phases.After natural aging,the formation of small GP zones is promoted,and the elongation of FSA samples is improved,and the corrosion resistance is close to that of RRA samples.The FSA specimen has the highest elongation(20.99%),and its strength is close to that of T6 specimen(tensile strength 426.08 MPa,yield strength 374.05 MPa).The corrosion resistance is close to that of RRA specimen,and its comprehensive performance is the best.Therefore,the heat treatment process of Al-Zn-Mg alloy that meets the requirements of modern industry is finally determined as follows:440?/12h+470?/24h(two-stage homogenization)+420? extruding+475?/2h(solution/water quenching)+105?/24h+170?/100 min+Na/24h+90?/7h(four-stage aging). |
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