| The 6066 aluminium alloy has excellent strength,good fatigue resistance and weldability due to its high alloying degree and the addition of more Si and Cu elements.It is an ideal material for transportation,aerospace and other fields.However,the corrosion resistance of 6066 alloy is not ideal.The alloy materials are prone to corrosion in complex natural environment caused by corrosion medium,which seriously affects the service life of materials and the safety of applications,and limits its application in automobile,high-speed train body structure parts,aircraft fuselage plate and so on.So it is of great significance to study how to improve its corrosion resistance without sacrificing the existing strength of 6066 alloy.Therefore,in order to improve the comprehensive performance of 6066 alloy,the contradiction between strength,plasticity and corrosion resistance of this kind of Al-Mg-Si-Cu alloy has been improved through microalloying,reasonable deformation mode and heat treatment process.The following work has been carried out in this paper:The 6066 aluminium alloy ingots with different Sr contents were prepared by ingot metallurgy.The ingots were homogenized,rolled and aged.The effects of Sr content and homogenization process on the as-cast structure and properties of Al-Mg-Si-Cu-Mn deformed aluminum alloy sheets were studied.The results show that the addition of 0.06 wt.% Sr in the alloy can transform the needle-likeβ-Si phase into spherical β-Si phase,and promote the formation of Al Fe Si spherical crystalline phase which improve the strength and plasticity of the alloy.After homogenization treatment,the Al(Mn Cr Fe)Si phase turns from the original trigonometric and needle-like phases into fine granular phases.The optimum homogenization heat treatment process for Al-Mg-Si-Cu-Mn-Sr alloy is 540℃×8h.The effects of Sr content on the microstructure and properties of Al-Mg-Si-Cu-Mn deformed aluminum alloy sheets after conventional solution aging treatment were studied.It was found that the plasticity of the alloy was improved with increasing Sr content.As the Sr content increases to 0.06 wt.%,the elongation of the alloy increased from 15% to 18%.The surface exfoliation corrosion morphology of the alloy with Sr addition was greatly improved.The maximum depth of intergranular corrosion was reduced from 213 μm to 200μm,and the corrosion resistance was improved.The effects of different solution aging processes on the corrosion resistance of the alloy were studied.Compared with conventional solid solution ageing treatment,the microstructure and properties of Al-1.0Mg-1.3Si-0.8Cu-0.6Mn-0.06 Sr alloy can be improved by high temperature pre-precipitation treatment or three-stage aging treatment,but the high temperature pre-precipitation treatment increases the production cost.Summary of above mentioned,the conventional solid solution+three-stage aging heat treatment system(540℃/1h+water quenching+140℃/6h+180℃/5h+140℃/4h)is the most suitable one.The tensile strength of the alloy was increased from 399 Mpa to429.6 Mpa;the elongation was increased from 18% to 21.2%.The intergranular corrosion performance grade was improved from 4 to 3 grades,and the exfoliation corrosion grade was improved from PC to PB. |
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