| Because of the features of simple preparation, easily processing, forming and less pollution to environment, the degradable materials are widely used in the field of energy source industry and oil-gas exploitation. The common degradable polymeric materials and biodegradable ceramics can not meet the operating requirements, because they are unable to bear high temperature and high pressure, easy deformation and restricted by the strict degradable condition. As a new kind of material, compared with the biodegradable polymer and ceramic materials, the degradable metal has a vast application space which caused deeply concerned because of the rich resource, low cost, good mechanical properties, excellent electrical and thermal properties, and the advantages of best adaptability to the degradable environment. However, the single structure and the unstable degradable performance of degradable metal constrainted its widely application in the field of oil-gas exploitation. In this paper, good comprehensive properties of degradable Al metal were prepared successfully through the method of casting and incorporation of alloy elements Ga, Sn and In.In this thesis, the degradable Al based alloy, which can be used in the oil-gas fracturing was prepared by casting method. The influences of alloy elements Sn, Ga and In and heat treatment process on the microstructure and performance of the Al matrix degradable alloy was studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy spectrum analysis (EDS) testing method. Combining the electrochemical polarization curve with corrosion microstructure morphology analysis, the degradable Al alloy corrosion behavior and related mechanism were discussed.The effect of Sn addition on the Al-Mg alloy matrix was investigated. With the increment of the content of Sn, the second phase Mg2Sn and a small amount of Sn appeared in the prepared alloy increasingly. The alloy matrix was refined significantly and corrosion potential negative shifted obviously, but the alloy dissolve performance was poorer. Based on the 12 wt.% of Sn content, with further introduction of 3 wt.% of element Ga, the corrosion potential of prepared alloy moved negative further. The alloy had a high solubility in water at 90? and its quality decreased by 50% within 90 min.In order to lower the degradable temperature of the prepared degradable Al alloy, different contents of alloy element In added in the Al-Mg-Ga-Sn alloy were studied. Electrochemical tests showed that with the increase of the content of In, the microstructure of the prepared alloy has been refined to a certain degree. Moreover, the corrosion potential was more negative and the dissolving rate was improved constantly. When the addition amount of In was 1.3 wt.%, the quality of the alloy decreased by 50% within 75 min in water at 90?, and the dissolution rate increased by 16.7% compared to the prepared alloy without element In. Besides, within 95 min at 70? in water, the quality of the alloy decreased by 50%.On the basis of consequences investigated above, the influence of the ratio of In and Sn on the microstructure and properties of the prepared degradable Al alloy was further researched. With increment of the ratio of Sn, the volume of Ga-In-Sn eutectic in prepared alloy increased gradually and the particle turned into a bar. But the electrochemical polarization curves showed that the alloy corrosion potential moved positively and the alloy activity decreased. When the ratio of Sn was reduced, the volume of eutectic decreased and the corrosion potential negative shifted. As the ratio of Ga, In and Sn was 9:6:4 and 15:3.5: 30 respectively, the degradable temperature of the prepared Al alloy reduced further, the quality of alloy within 440 min and 470 min decreased by 50% at 50? in water, respectively.The heat treatment results of the prepared degradable Al alloy showed that when the heat treated temperature increased from 300 to 500?, the size of aluminum matrix grain increased from 40?50 ?m to 70?80 ?m under same holding time. Meanwhile, the content of the second phase reduced significantly and the distribution of the second phase was more uniform. Electrochemical polarization curves showed that the corrosion potential moved slightly negative and the activity of the prepared degradable Al alloy increased. With the heat preservation time at 300? extended, polarization curves showed that the alloy corrosion potential negative shifted and the degradation activity increased. The corrosion reaction rate was greater than the as-cast obviously at 50? in the water. However, extending the heat preservation time at 500?, the rod-shaped second phase Mg2Sn turned into a sphere gradually and the contact area of spherical alloy and matrix reduced. The electrochemical test showed the corrosion potential of the alloy samples moved positively and its activity decreased.The corrosion behavior analysis of the degradable Al alloy by the polarization curves and corrosion microstructure showed that Mg2Sn alloy phase was cathode and Al matrix acted as anode during the corrosion process. The pitting corrosion reaction always started from the edge of Mg2Sn alloy phase and the extension of pitting on the matrix surface caused the uniform corrosion of the prepared degradable Al alloy. |
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