| In drilling process, traditional steel drilling tools easily have some problems suchas corrosion, cracking, fatigue break, etc. Because of high density, low strength ratioand some other disadvantages, steel drill can not play advantage in complex well anddeep well, so we should change the material of drill pipe to avoid those shortcomings.The project that design and development about under segment drill pipe material usedfrom200℃to250℃is accomplished in this paper, the acceptance evaluationindexes are: σb≥500MPa at25℃, δ≥8%; σb≥350MPa at200℃, σb≥200MPa at250℃.2000series aluminum alloys have low density, high strength ratio, corrosionresistance, good heat resistance and higher strength at room temperature, which is thebest to replace steel drilling tools. But2000series aluminum alloys can not work toolong time above150℃, or the strengthening phase will become coarse which mayresult in performance degradation. Comparing to2000series aluminum alloys,Al-Cu-Mg-Ag alloy has higher strength at room temperature and excellent heatresistance, so this alloy has a wide application prospect. In this paper, three alloys(1#,2#,6#) which have different composition of Cu and three other alloys(1#,2#,6#)which have the same composition as2#have different extrusion ratios are casting onthe basis of2024alloy by adding Ag and adjusting the composition.This paper studied the effect of homogenizing treatment at495℃for24h andextrusion on Al-Cu-Mg-Ag alloy. Homogenizing treatment eliminated dendritesegregation in the casting structure, making non-equilibrium phases dissolve into thealuminum matrix. The structure of alloys was elongated and refined in extrusionprocess.4#alloy with the extrusion ratio of30had the best performance in threeextrusion alloys.This paper studied the effect of T6heat treatment on the microstructure andhardness of Al-Cu-Mg-Ag alloy. The approximate scope of solution temperature ofseven alloys was determined in DSC curve analysis. The best solution temperature was determined by observing the number of residual phase and ensuring whether thealloys were over burning in metallographic microstructure analysis. The alloys wereanalyzed according to aging hardening result, and adding Ag not only acceleratedaging response rate, but also improved peak hardness at least13.9%. The best heattreatment process is: solution495℃×2h+aging185℃×8h(2024alloy), solution515℃×2h+aging185℃×4h (1#alloy), solution520℃×2h+aging185℃×4h(2#,3#,4#,5#and6#alloy).This paper studied mechanical properties of Al-Cu-Mg-Ag alloys both at roomtemperature and in high temperature, finding that Ag can significantly improvemechanical properties both at room temperature and in high temperature, and fracturesurfaces were observed by Scanning Electron Microscope to explain the changes ofplasticity. Compared with2024alloy, concluded that:(1) The strength of extrusionalloys at room temperature improved at least20%.(2) The strength of peak agingalloys at room temperature improved at least10%, and the performance of4#alloywas the best (σb=540MPa、σ0.2=460MPa、δ=21.5%).(3) The strength of peak agingalloys in high temperature improved significantly, and4#alloy had the bestperformance (σbimproved at least12.8%compared with2024alloy, σ0.2improved atleast25.1%compared with2024alloy, δ≥21.0%). The mechanical properties of4#alloy reached the acceptance evaluation indexes.This paper made a comparison on the alloys containing Ag, finding that tensilestrength and yield strength were higher when the temperature were150℃and200℃,and Ω phases were stable relatively. The strengthening phases were easy to coarseunder250℃, making the strength decrease rapidly. The main precipitated phase Ω ofthe alloys containing Ag were analyzed and making a quantitative analysis byTransmission Electron Microscope, the alloys precipitated large Ω phases and few θ′phases, the strength of the alloys increased with the increasing of Ω phase. |
PDF Full Text Request