| Aluminum alloy drill pipes are gradually being used in petroleum exploration due to their comprehensive performance.Al-Zn-Mg-Cu ultra-high strength aluminum alloy has become the most promising material for aluminum alloy oil drill pipe because of its excellent strength,hardness,ductility and toughness and corrosion resistance.In this paper,Al-Zn-Mg-Cu-Zr(-Er)aluminum alloy of petroleum drill pipe is used as the research object.And three groups of Al-Zn-Mg-Cu-Zr(-Er)aluminum alloys with different compositions were analyzed by OM,EBSD,SEM,TEM,Micro-hardness tester,conductivity meter,tensile tester,thermocouple recorder and other analytical test methods.The effects of different solution temperature,heating rate and quenching cooling rate on the microstructure,mechanical properties(hardness,strength,elongation),electrical conductivity and resistance to intergranular corrosion were characterized and analyzed in detail.The main research results are as follows:(1)470?is the best temperature for the single-stage solution treatment of Al-Zn-Mg-Cu-Zr(-Er)aluminum alloy.When solid solution in the temperature range of460?-480?,the undissolved second phase in the alloy gradually dissolves with increasing temperature,the supersaturation of the alloy gradually increases,the conductivity gradually decreases,and the recrystallization fraction also increases.Under the combined influence of solid solution strengthening and recrystallization softening,the hardness,strength,and elongation of the alloy peak at a solid solution temperature of 470?.The alloy 2 and alloy 3 with Er element(0.08%Er,0.13%Er,respectively)are significantly less recrystallized than the alloy 1 without Er,indicating that the addition of Er element can effectively suppress the re-recrystallization and crystallization The migration and merging of the boundary keep the alloy in a fibrous structure obtained from the extrusion.(2)In the solution process,with the increase of the solution heating rate,the elongated grain structure in the alloy gradually decreases,the approximately equiaxed recrystallized grain structure gradually increases,the average grain size decreases,and the amount and size of the residual second phase particles after quenching are reduced.The alloys treated by different heating rates have little difference in hardness after quenching.(3)When the quenching rate is reduced,coarse?equilibrium phases are mainly precipitated on the(sub)grain boundary and Al3(Er,Zr)particles.These equilibrium phases reduce the concentration of solute atoms and vacancies,which causes the uneven and continued distribution of precipitated phases in the grain boundary,and the width of the PFZ becomes wider.(4)After quenching into different quenching media,the mechanical properties of the room temperature water-quenched alloy are the best,the oil-quenched alloy is the second,and the air-quenched alloy is the worst.At the same time,the intergranular corrosion resistance of the alloy is significantly enhanced with the increase of quenching rate and Er content.(5)In the range of 0%-0.13%Er,with the increase of Er element content in Al-Zn-Mg-Cu-Zr alloy,the mechanical properties of the alloy are improved,the volume fraction of recrystallized grain structure decreases,the average grain size decreases,and the corrosion resistance has improved. |
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