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Study on the resistance and properties of aluminum alloy for oil drill pipe

Author: WangHeng
Tutor: LiuZhiYi
School: Central South University
Course: Materials Science
Keywords: Al-Cu-Mg alloy yield strength thermal exposure fatigue strength
CLC: TG146.21
Type: Master's thesis
Year: 2012
Downloads: 52
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Abstract


Compared to traditional steel drill pipe, Aluminum drill pipe takes advantage for its lower specific strength, excellent resistance to fatigue damage and corrosion. As the geothermal industry develops, demands for deeper drilling and heat-resistance become forceful day by day, this is where Al-Cu-Mg alloy drill pipe can become a benefit.The effect of thermal-mechanical treatment on mechanical properties and micro-structural thermal-stability of2D12and2A12alloys was systematically investigated through methods of hardness and tensile test, DSC, optical microscopy, TEM and SEM used.Clusters formation was entirely restrained by pre-deformation, while heterogeneous precipitation of S phase was vastly promoted. Yielding was obviously retarded because slipping was difficult to start for the existing of dispersive S phase. Energy for starting of slipping went down as the temperature rose, thus difference between yield strength of T6and T8alloys reduced. Through4%pre-stretching, tensile strength and yield strength of160℃peak-aged2D12alloy were accelerated by23MPa and138MPa respectively, with15MPa and152MPa for190℃.In tensile test at elevated temperatures up to150℃and200℃,yield strength was increased by103MPa and66MPa with4%pre-deformed.Pre-deformation introduced finer more dispersive S phase with better uniformity and lower coarsening rate. Meanwhile, solute concentration in the matrix had declined to some extent with fully precipitation induced by the abundant dislocation introduce by pre-deformation, which made the demand of solute for precipitates coarsening difficult to satisfy, thus the precipitates coarsened more slowly than those in T6alloy. For2D12alloy,T8samples exposed at200℃for500h remained85%of its original tensile strength with T6samples77%.For2A12alloy,T8samples exposed at200℃for500h remained77%of its original tensile strength with T6samples71%.Mechanical properties of2A12alloy exposed at200℃for500h advanced totally while those subjected to160℃and200℃exposure declined.Fatigue lives of2A12alloy bars lessened as axial stress rose, and fatigue life corresponding to stress level lower than350MPa was enhanced by pre-deformation treatment. At higher stress level of420MPa, both T6and T8samples possessed similar lives about105, while at lower stress level of280MPa, T8bars subjected to more cyclic times. Fatigue strength of T6samples reached220MPa when subjected to stress cyclic loading of107times while T8samples nearly reached280MPa.Good comprehensive mechanical properties were performed on Al-4.2Cu-1.5Mg (wt.%) alloy, while Al-4.9Cu-1.8Mg (wt.%) alloy lost ductility dramatically with higher strength gained, which meant its incompetence of long-term service in thermal environment. Meanwhile, Zr was kind of helpful for the durability of the alloy expected to serve in such conditions, for considerable strength was retained during thermal exposure, comparing to alloys without Zr who possessed higher peak-aging strength.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Aluminum
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