Effect Of Deformation And Aging On Mechanical And Corrosion Properties Of Al-Mg-Si-Cu Alloy

The age-hardening Al-Mg-Si-Cu aluminum alloy has high specific strength,good formability,weldability and corrosion resistance,so it is widely used in the fields of aerospace and vehicle manufacturing.Increasing the Cu content can improve the strength,but it leads to an increase in the alloy's intergranular corrosion sensitivity.Over-aging the alloy can improve the corrosion resistance,but it will reduce the strength.Therefore,how to obtain high-strength,high-toughness,and corrosion-resistant Al-Mg-Si-Cu alloy has attracted wide attention.The properties of mechanical and corrosion of Al-Mg-Si-Cu alloys were investigated by tensile test and IGC test.And the microstructure was characterized by means of metallography,Scanning Electron Microscopy(SEM),Energy Dispersive Spectrometer(EDS),Transmission Electron Microscopy(TEM).Study the effect of thermo mechanical treatment on the microstructure and properties of the alloy,the experimental results are as follows:(1)After the alloy is solution treated at 540 ?/1 h,it is subjected to single-stage aging treatment at 180 ?-210 ?/1-10 h.Alloy strength and IGC sensitivity increase first and then decrease.After aging at 180 ?/6 h(T6),the tensile strength,yield strength and elongation are 387 MPa,368 MPa and 14% respectively,but severe IGC occurred.The alloy can obtain the best combination of strength and IGC resistance.The tensile strength,yield strength and elongation are 374 MPa,359 MPa and 9.9% respectively,and the corrosion mode is uniform corrosion.The precipitated phases of the alloy matrix are uniformly distributed ?' phase and Q' phase,and the grain boundary precipitated phases are spherical and intermittently distributed,which make the alloy obtain high strength and good intergranular corrosion resistance.(2)To improve alloy mechanics and corrosion properties at the same time,solution treatment(540 ?/1 h)+cold rolling deformation(80%reduction)+re-aging is adopted,which introduce dislocation strengthening and precipitation strengthening.Experiments have found that the re-aging temperature has a greater impact on the properties of the alloy.When high temperature(190 ?,200 ?,210 ?)is selected for re-aging treatment,the alloy strength and intergranular corrosion sensitivity change rapidly,showing a trend of increasing first and then decreasing.After re-ageing treatment at190 ?/10 min,the tensile strength and,yield strength of the alloy are 421 MPa and 406 MPa.Compared with T6 state,increased by 8.8% and 10.3%respectively,but the intergranular corrosion sensitivity is high.Continued ageing,the corrosion mode changed from intergranular corrosion to pitting corrosion,and the degree of corrosion was reduced.The main reason is that after cold rolling deformation,a large number of dislocations are introduced.When re-aging,the coarsening of the precipitated phase of the matrix is accelerated.Electric potential difference is generated locally,which leads to pitting corrosion of the alloy.(3)ST+CR+low temperature re-aging(80-110 ?/0-120 h)can slow down the precipitation rate of the precipitated phase at the grain boundary and improve the alloy mechanical and corrosion properties.The intergranular corrosion susceptibility gradually increases,and the alloy strength first increases and then decreases.After re-ageing treatment at 95 ?/24 h,the alloy has achieved the best combination of mechanical and corrosion properties.The tensile strength,yield strength and elongation are 420 MPa,391 MPa,and 9% respectively,and the alloy has good corrosion resistance.