Study On Microstructure And Properties Of High Strength And Toughness Al-Mg-Si-Cu Alloy

6XXX series Al-Mg-Si alloy has the advantages of medium strength,excellent formability and good corrosion resistance.As more and more 6XXX series aluminum alloys are used in the automobile manufacturing industry,the requirements for the strength of aluminum alloys for automotive parts are becoming higher and higher.In order to improve the strength of aluminum alloys,the content of Cu in Al-Mg-Si-Cu alloys is also increasing.When the content of Cu increases,the alloy's resistance to intergranular corrosion decreases sharply,and the toughness of the alloy also decreases.This subject mainly improves the alloy strength by adjusting the content of Cu element,and improves the corrosion resistance of the alloy by introducing Zn element.After twostep homogenization treatment,T6 and T78 aging treatment,the alloy composition and aging heat treatment process with the best comprehensive performance are obtained.The main research results of this topic are as follows:(1)The second phase in the as-cast Al-Mg-Si-Cu alloy is Mg2Si phase,Al(Mn,Fe)Si phase,and Q phase(AlCuMgSi phase).When the Cu content reaches 0.8wt.%and above,Al2Cu phase appears in the microstructure.(2)After the first-step homogenization of Al-Mg-Si-Cu alloy at 490?/10h,the Q phase in the alloy is partially converted into Mg2Si phase,and the remaining Q phase is all dissolved back into the aluminum matrix,and the Al2Cu phase is completely recovered.Dissolved into the aluminum matrix,part of the bulk AI(Mn,Fe)Si phase distributed on the grain boundaries was spheroidized and aggregated into spherical Al(Mn,Fe)Si phase.After the alloy was homogenized at 490?/10h+560?/12h,the Mg2Si phase in the alloy was basically dissolved back into the aluminum matrix,and the massive Al(Mn,Fe)Si phase continuously distributed on the grain boundary was completely broken,and a large number of pieces The Al(Mn,Fe)Si phase is transformed into a spherical Al(Mn,Fe)Si phase.The best two-step homogenization process of Al-Mg-Si-Cu alloy in this experiment is 490?/10h+560?/12h.(3)The optimal T6 aging temperature of Al-Mg-Si-Cu alloy is 180?.With the increase of Cu content,the peak aging time of the alloy is 6h.The tensile strength and yield strength of the peak aging increase simultaneously,but after breaking,The elongation decreased slightly.With the increase of Zn content,the peak aging time of the alloy was shortened from 6h to 5h,and the tensile strength,yield strength and elongation at break of the peak aging did not change significantly.The post-break elongation of the alloy is greater than 15%,which improves the strength of the alloy while maintaining a good plastic deformation ability.(4)After Al-Mg-Si-Cu alloy undergoes two-stage aging heat treatment of T6 and T78,the maximum intergranular corrosion depth of the alloy increases with the increase of Cu content;as the Zn content increases,the maximum intergranular corrosion depth decreases.small.Compared with T6 peak aging,after T78 two-step aging heat treatment,the alloy strength is slightly reduced(up to 6%),but the intergranular corrosion resistance of the alloy is significantly improved(at least 15%),and the alloy's self-corrosion potential becomes Correction(at least 14%),reduced corrosion current density(at least 62%).(5)Considering the strength of the alloy and the resistance to intergranular corrosion,the optimal alloy composition for this experiment is 1.2Cu 0.5Zn alloy.After the alloy was homogenized at 490?/10h+560?/12h in two-step,after 550?/40min solution treatment and 180?/4h+210?/2h in two-step aging heat treatment,compared with the T6 state,the strength of the alloy was reduced by 3.47%to 413.9MPa;the maximum depth of intergranular corrosion decreased by 17.5%to 104 ?m.The alloy meets the requirements for the strength and plastic deformation ability of automotive sheet materials,and has certain resistance to intergranular corrosion.