Effect Of Heat Treatment On Stress Corrosion Of Al-5.8Zn-2.7Mg-1.6Cu Aluminum Alloy

In this paper,the effect of heat treatment on the stress corrosion of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy was studied.The microstructure and phase composition of the aluminum alloy were studied by optical microscopy,electron scanning microscopy analysis.The mechanical property of the aluminum alloy was tested by tensile test.The resistance to stress corrosion of the aluminum alloy was studied by the slow strain rate testing(SSRT).The hardness and electrical conductivity of the alloy were also tested.By analyzing the experimental results,the heat treatment processing parameters of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy with good mechanical property and resistance to stress corrosion were obtained.The main conclusions are as follows:(1)The effect of high temperature pre-precipitation on the stress corrosion resistance of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy was investigated.High temperature pre-precipitation can change the size and distribution of precipitates in the crystal and grain boundary.It can also inhibit the dissolution of the anode and the hydrogen embrittlement to improve the mechanical property and resistance to stress corrosion of the alloy.When the pre-precipitation temperature is 420℃,the stress corrosion sensitivity of the alloy after high temperature pre-precipitation treatment is the lowest,which can increase the resistance to stress corrosion of the alloy,but its strength and hardness are reduced.To obtain the best resistance to stress corrosion of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy,the high temperature pre-precipitation processing parameters are 470℃×1h+420℃×0.5h.(2)The effect of two-stage solid solution on the resistance to stress corrosion of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy was investigated.The first-order solution time and secondary solution time in two-stage solid solution are the most important factors affecting the property of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy.One of the purpose of the two-stage solid solution is to recover in the first-order solid solution stage,consume the deformation energy storage and reduce the recrystallization driving force.The other purpose is to allow the crystal phase to dissolve in the matrix in a certain order,improve the solution temperature and dissolve the second phase.The results of orthogonal test show that the two-stage solid solution process parameters of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy with the best strength are 440℃×90min+470℃×50min.To obtain the best resistance to stress corrosion of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy,the two-stage solid solution processing parameters are 450℃×120min +470℃×40min.(3)The pre-aging time and the retrogression temperature in the retrogression and re-aging are the most important factors affecting the properties of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy.Through the results of the orthogonal test,the processing parameters of retrogression and re-aging of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy with the best resistance to stress corrosion are 120℃×24h+185℃×1h+120℃×18h.(4)The best heat treatment processing parameters of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy with excellent resistance to stress corrosion are as follows:two-stage solid solution(450℃×120min + 470℃×40min)and retrogression and re-aging(120℃×24h + 185℃×1h+ 120℃×18h).(5)In the low temperature corrosive environment,the strength of Al-5.8Zn-2.7Mg-1.6Cu aluminum alloy is improved,but its elongation is decreased.The stress corrosion sensitivity is also improved,and the resistance to stress corrosion is reduced.