Study On The Hardening Behaviors,Mechanical Properties And Corrosion Resistance Of Two-stage Creep-aged 7050 Alloys With Sc Addition

Three kinds of 7050 aluminium alloy plates containing different contents of scandium were prepared by adding scandium to the 7050 aluminium alloy with the standard chemical compositions.The effects of first-stage aging temperature,Sc content,stress and strain states on the age-hardening behavior,tensile properties and corrosion resistance of the alloys were investgatied through the two-stage creep-aging treatment of the alloy plates in this study.The main research contents and results are summarized as follows.1.The effects of the first-stage aging temperature,Sc content,stress and strain states on the two-stage creep age-hardening behavior of the alloy were studied.The results showed that the hardness of the alloy increased at first and then decreased with the increase of the first-stage aging temperature.When the firest-stage aging temperature was 70 C,the hardness of the alloy was the highest.The addition of Sc element could improve the hardness of the alloy.And the hardness of the alloy is higher when Sc content was 0.18 wt.%.Compared with the stress-free two-stage aged alloy,the hardness of the two-stage creep-aged alloy decreased.But the hardness of the alloy two-stage creep-aged in the state of elastic strain was higher than that in elastic-plastic strain state.2.The effects of the first-stage aging temperature,Sc content and strain state on the tensile properties of the two-stage creep-aged alloys were investigated.The results revealed that the stress-free two-stage aged alloys had better tensile property when firststage aging temperature was 110?.But if the two-stage creep-aging was carried out in the state of elastic strain,the alloys had better tensile property when the first-stage aging temperature was 70?.If the two-stage creep-aging was executed in the state of elasticplastic strain,the room temperature as the first-stage aging temperature could make the alloys have better tensile property.For both the stress-free two-stage aged alloy and the two-stage creep-aged alloy,Sc addition all could improve the tensile properties of the alloys.The strength of the alloy was higher when Sc content was of 0.18 wt.%.For elongation,the stress-free two-stage aged alloy containing Sc content of 0.18 wt.% had a higher elongation.However,the elongation of the two-stage creep-aged alloy containing Sc content of 0.29 wt.% was higher.The yield strength and tensile strength of the stress-free two-stage aged alloy was all higher.The alloy two-stage creep-aged in the state of elastic strain had a higher elongation,and its tensile property was better than that of the alloy two-stage creep-aged in the state of elastic-plastic strain.3.The effects of the firest-stage aging temperature,stress state and strain state on the intergranular corrosion,exfoliation corrosion and electrochemical behavior of the alloys were researched.The results indicated that for the stress-free two-stage aged alloys,the corrosion resistance of the alloys was the best when thirs-stage aging temperature was 70?.However,the corrosion resistance of the alloys is the best when the first-stage aging temperature was room temperature for the two-stage creep-aged alloys,and the corrosion resistance of the alloys worsened with the increase of the firststage aging temperature.Compared with the stress-free two-stage aging,the two-stage creep-aging improved the corrosion resistance of the 7050 alloys containing scandium under the same conditions,and the corrosion resistance of the alloy two-stage creepaged in the state of elastic strain was better than that in the state of elastic-plastic strain.The corrosion resistance of the two-stage creep-aged alloy under compressive stress state exceled that under tensile stress state.