Effect Of Zn Aging System On Corrosion Properties Of Al-Mg-Si-Cu Alloy

Traditional 6xxx series aluminum alloys have high specific strength,formability and good welding performance,high impact toughness,and can be extruded into various complex profiles.With the continuous discovery of lightweight vehicles,higher requirements have been placed on the strength and corrosion resistance of aluminum alloys.For this reason,the Cu element is added to the Al-Mg-Si alloy to improve the strength of the material.However,with the increase of Cu element,the intergranular corrosion resistance of the alloy decreases sharply.The intergranular corrosion of the alloy is mainly caused by the potential difference between the precipitated phase at the grain boundary and the adjacent PFZs.Therefore,reducing the potential difference between them and changing the distribution and morphology of the precipitated phase are important to the corrosion resistance of the alloy.In this experiment,the corrosion resistance of Al-Mg-Si-Cu alloy was studied by adding different Zn elements to adjust the potential,and using different aging systems to change the state of grain boundary precipitation.The following conclusions were reached:(1)Zn does not form and does not change the as-cast structure of Al-Mg-Si-Cu alloys:Al2Cu,Mg2Si,Si,AlFeMnSi,AlMgSiCu.The best homogenization system of Al-Mg-Si-Cu alloy is:470?/4 h+560?/12 h.(2)When artificial aging at 180?,the Zn element can increase the hardening response rate of the alloy,but it has little effect on the peak hardness.The peak time of 0-0.2 wt.%Zn alloy is 6 h,and the peak time of 0.25?1.0 wt.%Zn alloy is 5 h.0 wt.%Zn alloy peak hardness is 149.5 HV,1.0 wt.%Zn alloy peak hardness is 150.02 HV(3)Accelerated corrosion experiments show that under 180? artificial aging,the alloy's corrosion resistance:under aging>over aging>peak aging.The maximum corrosion depth of the alloy is different with different Zn content,and it tends to decrease and increase with the increase of Zn content.Maximum corrosion depth of Al-Mg-Si-Cu alloy under peak aging state:0 wt.%Zn is 229 ?m,0.25 wt.%Zn is 143 ?m,and 1.0 wt.%Zn is 259 ?m.As the Zn content increases,the corrosion potential moves first and then negatively.As the Zn content increases,the corrosion current density decreases first and then increases.Comprehensive accelerated corrosion and electrochemical experiment results show that the corrosion resistance is best when the Zn content is 0.25 wt.%.(4)Al-Mg-Si-Cu alloy was subjected to T78 aging treatment,and the hardness of the alloy was 146.48 HV.As the second-stage temperature increases,the hardness of the alloy decreases,and the electrical conductivity is generally higher than the peak of T6.The best system is determined:180 ?/4 h+190 ?/0.5 h.Compared with the T6 peak alloy,the corrosion resistance of the alloy is improved in the T78,the maximum depth is 132 ?m,and the corrosion depth is reduced by 42.4%.The tensile strength of Al-Mg-Si-Cu alloy at the peak of T6 is 423.3 MPa,and at T78 it is 412.74 MPa,which is only a decrease of 10.56 MPa.