时效对铝合金钻杆用Al-7.51Zn-2.37Mg-1.72Cu合金力学及耐热性能的影响

Effect of aging on mechanical properties and thermal stability of Al-7.51Zn-2.37Mg-1.72Cu aluminum alloy used for drill pipe

摘要:

铝合金材料是航空、航天、轨道交通、石油工业等领域的研究热点,具有密度低,比强度高,耐腐蚀性能好等优点。本文针对7xxx系铝合金设计出一种适用于油气工业环境的钻杆材料—Al-7.51Zn-2.37Mg-1.72Cu。通过时效硬化行为、力学性能评价及微观组织表征研究了时效处理对铝合金钻杆材料力学性能及耐热性能的影响。结果表明,时效温度为120℃时Al-7.51Zn-2.37Mg-1.72Cu的最佳时效时间为24h,其抗拉强度、屈服强度和伸长率(R_m、R_0.2和A)分别由淬火态的693MPa、566MPa和15%变化到720MPa、692MPa和14%；再经200℃热暴露500h后,R_m、R_0.2相比时效态降低了55.6%、 67.3%,伸长率提高了15.8%,这是由于基体内GP区和部分细小η′相开始发生回溶,而尺寸较大稳定性较高的η 相会转变成η′ 相,部分η 相会聚集成粗大质点。

Abstract:

Aluminum alloy materials have the advantages of low density, high specific strength, good corrosion resistance, etc., which are currently a hot spot especially in industrial research. In this paper, an Al-7.51Zn-2.37Mg-1.72Cu drill pipe material suitable for the oil and gas industry is designed for the 7xxx series aluminum alloy. The effect of aging treatment on the mechanical properties and thermal stability of aluminum alloy drill pipe materials was studied through age hardening behavior, mechanical performance evaluation and microstructure characterization. The results show that the optimal aging time of Al-7.51Zn-2.37Mg-1.72Cu is 24h when the aging temperature is 120℃. The tensile strength, yield strength and elongation (R_m, R_0.2 and A) of the quenched state changes from 693MPa, 566MPa and 15% to 720MPa, 692MPa and 14%, respectively. After 500 hours of heat exposure at 200℃, R_m and R_0.2 are reduced by 55.6% and 67.3% compared with the aging state, and the elongation is increased by 15.8% on average. This is mainly because the GP zone in the alloy matrix and some of the small and poorly stable η" phases begin to re-dissolve, and the larger and more stable η phase will transform into η" phase. At the same time, the existing η phases in the matrix converge into large mass points.