The Influence Mechanism Of SiC Particles On The Corrosion Behavior And Mechanism Of Al-Cu-Mg Aluminum Alloy For Drill Pipe

Due to its low density, high specific strength, high flexibility, anti fatigue and excellent technological properties, aluminum alloy has become one of the preferred materials for the drill pipe of deep and ultra deep wells. But the aluminum alloy has the disadvantages of low hardness and poor wear resistance. The aluminum matrix composites formed by the addition of SiC particles have the advantages of aluminum alloy and improve its hardness and wear resistance. However, as with the steel drill pipe, the aluminum alloy drill pipe is also facing the problem of corrosion in the process of using. So the study on the corrosion behavior of aluminum alloy and its composites for the drill pipe and the influence mechanism of SiC particles on the corrosion behavior and mechanism is very necessary and meaningful.In this study, the effect of the addition of SiC particles on the microstructure of Al-Cu-Mg aluminum alloy was studied by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). Secondly, the uniform corrosion, pitting corrosion and intergranular corrosion behaviors of Al-Cu-Mg aluminum alloy and SiCp/Al-Cu-Mg composite in different temperature of 3.5 wt.% NaCl solution and polysulfonate drilling fluid were studied and compared by using optical microscope, SEM, EDS, XRD, X-ray CT and electrochemical workstation. Finally, the corrosion mechanisms of the two materials and the effect of SiC particles on the corrosion behavior and mechanism of aluminum alloy were discussed.Research showed that:the second phases in the Al-Cu-Mg aluminum alloy included θ(CuAl2) phase, S(Al2CuMg) phase and T(AlZnMgCu) phase. The second phase existed in SiCp/Al-Cu-Mg composites was mainly θ(CuAl2) phase. The addition of SiC particles inhibited the formation of S(Al2CuMg) and T(AlZnMgCu) phases, which changed the microstructure and improved the corrosion resistance. Uniform corrosion occurred in the early stage of Al-Cu-Mg aluminum alloy and SiCp/Al-Cu-Mg composite material in the 3.5 wt.% NaCl solution and the polysulfonate drilling fluid. The corrosion rate increased with the increase of temperature. With the extension of time, the pitting corrosion occurred on the surface of the specimens. And with the increase of temperature, the density and depth of the pits were increased, especially the high temperature had a significant effect on the occurrence and development of the pitting corrosion of the materials. In addition, the corrosion degree of the two materials in the polymer drilling fluid was significantly lower than that in the 3.5 wt.% NaCl solution under the same conditions. The intergranular corrosion occurred when Al-Cu-Mg aluminum alloy and SiCp/Al-Cu-Mg composite material in NaCl+H2O2 solution with high temperature. The intergranular corrosion depth increased with the increase of temperature. Generally speaking, the corrosion resistance of SiCp/Al-Cu-Mg composites was better than that of Al-Cu-Mg aluminum alloy.The corrosion of Al-Cu-Mg aluminum alloy mainly started from the region existed 6(CuAl2) phase、S(Al2CuMg) phase、T(AlZnMgCu) phase and β(Mg2Si) phase or surface defects. The corrosion of SiCp/Al-Cu-Mg composites mainly started from the places existed the θ(CuAl2) phase or surface defects around the SiC particles. However, the addition of SiC particles inhibited the formation of S (Al2CuMg) phase and T (AlZnMgCu) phase and made the θ(CuAl2) phase refined. Therefore, in general, the addition of SiC particles improved the corrosion resistance of Al-Cu-Mg aluminum alloy.