Effect Of Heat Treatment On Microstructure And Properties Of Al-6Zn-2Mg-2Cu Welded Joint

Al-Zn-Mg-Cu alloy has ultra-high-strength.It is widely used in aerospace and other engineering fields.However,after the alloy is welded,the mechanical properties and corrosion resistance of the welded joint are weakened obviously,which seriously restricts the applied alloys.The microstructure and properties of tungsten inert gas welding joints of Al-6Zn-2Mg-2Cu alloy that had undergone different post-weld heat treatments had been studied in this paper,the influence of heat treatment process on microstructure and properties was analyzed,the mechanical properties were tested by hardness and wear resistance experiments,and the corrosion resistance was tested by intergranular corrosion,exfoliation corrosion and electrochemical corrosion experiments.The research results showed that the microstructure of the welded joint of Al-6Zn-2Mg-2Cu alloy after post-weld heat treatment could be significantly improved,and the mechanical properties and corrosion resistance were also improved.The resist intergranular corrosion,exfoliation corrosion and electrochemical corrosion after two-stage solid solution and regression re-aging treatment（450℃×1.5h+480℃×0.5h+120℃×24h+190℃×40min+120℃×24h）were the best.The mechanical properties after two-stage solution and single-stage aging treatment（450℃×1.5h+480℃×0.5h+120℃×24h）was the best.After post-weld heat treatment,the grains of the welded joints could be made finer,and the strengthening phase Mg Zn₂ could be precipitated at the grain boundaries.Heat treatment could affect the generation and distribution of precipitation-free zones around grain boundaries.The two-stage solid solution regression and re-aging treatment had uniform grain size distribution,discontinuous distribution of precipitates at the grain boundaries,and the number of precipitation-free zones was the largest,and it was wider than those of the other three kinds of heat-treated samples.The maximum hardness of the welded joint after two-stage solution and single-stage aging treatment was 120.8HV,which was 50%higher than that of the welded state.The friction coefficient was 0.708,and the wear resistance was also the best.The two-stage solution regression and re-aging treatment of the alloy showed good corrosion resistance in all three corrosion tests,the intergranular corrosion grade was 3,the exfoliation corrosion grade was PA,and the electrochemical corrosion tendency was the smallest.To improve the comprehensive properties of the welded joint of Al-6Zn-2Mg-2Cu alloy,the best heat treatment was two-stage solid solution regression and re-aging treatment.