Research On Mechanisms Of Heat And Corrosion Resistance Of Al-Cu-Mg-(Ag) Alloys For Oil Well Pipe

As the drilling environment of oil resources becomes more complex,higher requirements have been put forward for heat resistance and corrosion resistance of Al-Cu-Mg series alloy oil well pipe materials.Therefore,tensile test at room temperature/high temperature,thermal exposure test,immersion corrosion,intergranular corrosion,exfoliation corrosion and other experimental methods are adopted in this dissertation.The effects of Cr micro-alloying,hot rolling temperature and pre-stretch deformation on mechanical and corrosion properties of Al-Cu-Mg-（Ag）alloy are investigated.In the meantime,the relationship between microstructure and heat resistance,corrosion resistance of the alloy has been studied by means of synchronous thermal analyzer,X-Ray Diffractometer,scanning electron microscope and transmission electron microscope.The main conclusions are summarized as follows:（1）The addition of minor Cr promotes the formation of S phase in Al-Cu-Mg alloy,which improves the strength of the alloy at room temperature and high temperature,but causes relatively little plastic change.The residual tensile properties of the alloy are also improved after exposing at200℃,which is mainly attributed to the relatively slow coarsening rate of S phase.The discontinuous distribution of grain boundary particles impedes the fast connection of corrosion channels and improves the corrosion resistance of Cr-containing alloy.（2）With the decrease of rolling temperatures（470℃,440℃and410℃）,the tensile properties of Al-Cu-Mg-Ag alloy at room temperature and high temperature have little change.However,the corrosion resistance of the alloy is significantly improved.The maximum intergranular corrosion depths are 364μm,271μm and 246μm,and the corrosion current densities are 2.56,1.91 and 1.30μA·cm^-2,respectively.Due to the existence of high proportion of low-angle grain boundaries and discontinuous distribution of grain boundary particles,the under-aged alloy rolled at 410℃has the strongest corrosion resistance.（3）With the increase of the pre-stretch deformation（0～4%）,the introduced dislocations promote the heterogenous nucleation of the S phase.The yield strength of Al-Cu-Mg-Ag alloy at room temperature and high temperature increases by 22.8%and 21.6%（at 200℃）,respectively.As for tensile strength and elongation,the variation is small.The heat resistance of the alloy is also improved,which is due to the slow coarsening rate of the fine S phase with high volume fraction in the pre-stretched specimen.However,due to the anodic dissolution of S phase at the matrix and grain boundary,the introduction of pre-stretching will lead to the degradation of the corrosion properties for the alloy.