Study On The Corrosion Resistance Of Creep-aging Processed 7050 Aluminum Alloy With Sc Addition

7050 alloy is a kind of high strength aluminum alloy that is widely used in aerospace field.The author of this paper prepared three types of 7050 alloys with various contents of Sc based on the standard composition of 7050 alloy by adding Sc.The effects of Sc on the microstructures and mechanical properties of the 7050 alloy were investigated.And through processing the prepared alloys with creep-ageing technology,the effects of Sc content,deformation(represented in press distance)and stress state on the intergranular corrosion,exfoliation corrosion and stress corrosion behaviours of the creep-aging processed 7050 alloy with Sc addition were comparatively studied.The main studying contents and results are summarized below.(1)The effect of Sc on the microstructure and mechanical properties of 7050 alloy was investigated.The results showed that adding small amount of Sc to 7050 alloy significantly refined the as-cast microstructure of the alloy,and with the increase of Sc content,the refining effectiveness became stronger.The fibrous microstructures of the deformation processed 7050 alloys with Sc addition were also finer and more uniform.Compared with 7050 alloy without Sc addition,the hardness and tensile property of 7050 alloy with Sc addition were all significantly improved.And when Sc content is of 0.18 wt.%,the mechanical properties of the 7050 alloy was the best.However,the mechanical properties of the 7050 alloy could not be further improved when more content of Sc was added to the alloy,but had a tendency to decline.(2)Though processing the prepared alloys with creep-ageing technology,the effect of Sc content on the intergranular corrosion,exfoliation corrosion behaviours of the creep-ageing processed 7050 alloy with Sc addition was comparatively studied.The results indicated that the intergranular corrosion and exfoliation corrosion resistances of the creep-ageing processed 7050 alloys with Sc addition were obviously superior to those of 7050 alloy without Sc addition,and with the increase of the Sc content,the intergranular corrosion and exfoliation corrosion resistances of the alloys were slightly enhanced.(3)The effect of deformation during creep-ageing processing on the intergranular corrosion and exfoliation corrosion resistances of the tested alloys was studied.The results showed that 7050 alloys with and without Sc addition all had the strongest intergranular corrosion and exfoliation corrosion resistances when the deformation was in the critical zone of elastic and plastic deformation(the press distance is about7mm).But,when the creep-ageing processing of the alloys was carried out in the plastic deformation area of the alloys(such as the press distance is 12mm),the intergranular corrosion and exfoliation corrosion resistances of 7050 alloys with and without Sc addition slightly decreased.When the deformation of the alloys was in the elastic range(the press distance is 0 to 5mm),the effect of deformation on the intergranular corrosion and exfoliation corrosion resistances of the 7050 alloys with and without Sc addition was slightly different.For the alloy without Sc addition,the increase of deformation enhanced the corrosion resistances of the alloys.But for the alloys with Sc addition,the increase of deformation reduced the corrosion resistances of the alloys.(4)The effect of stress state during creep-ageing processing on the intergranular corrosion and exfoliation corrosion resistances of the tested alloys was investigated.The results suggested that the intergranular corrosion and exfoliation corrosion resistances of the alloy that is in a compressive stress state during creep-ageing processing be all superior to those of the alloy that is in a tensile stress state.(5)The effects of Sc content and deformation on stress corrosion cracking(SCC)of the creep-ageing processed 7050 alloys with Sc addition were comparatively studied with slow strain rate tension test.The results presented that Sc addition obviously reduced the susceptive indexes of SCC of 7050 alloy under the same deformation,and thus enhanced the SCC resistance of the alloy.And the proper increase of Sc content was beneficial to reducing the SCC susceptibility of the alloy.In the condition of the same Sc content,the effect of deformation on the SCC susceptibility of the creep-ageing processed 7050 alloy with and without Sc addition had a similar variation trend.When the deformation is in the elastic range(the press distance is 0 to5mm),the SCC susceptibility of the alloy rised with the increase of deformation.When the deformation is increased to the critical zone of elastic and plastic deformation(the press distance is about 7mm),the SCC susceptibility of the alloy significantly reduced.But,when the deformation was further increased to the plastic deformation range(such as the press distance is 12mm),the SCC susceptibility of the alloy rises obviously again.