Effects Of Trace Rare Earth On Mechanical Properties Of 049 And 7055 Alloys Before And After Thermal Exposure

Deep well drilling is becoming an important method for oil mining with development of energy and oil industry,which need Al alloy drilling pipes with high strength and low density.Based on the this demand,effects of trace rare earth elements on mechanical properties of 049 and 7055 alloys before and after thermal exposure were studied in this paper to provide the theoretical and experimental foundation for alloy selection of Al alloy drilling pipes.The main results are as followings:(1)The tensile strengths of 049 alloy 1 containing 0.4wt.%Ag,the alloy2 containing 0.2wt.%Ag+0.05wt.%La and the alloy3 containing 0.1wt.%La without Ag,are 611.13MPa.615.55MPa and 591.91MPa after T6 treatment,are 642.43MPa、627.36MPa and 616.62MPa after T8 treatment respectively,which shows strengthening effect of Ag is higher than that of La.(2)Strengths of 049 alloy,the alloy containing 0.2wt.%Ag+0.05wt.%La increase after thermal exposure at 160℃ for 24 hours,are same as T6 condition after thermal exposure at 175℃ for 24 hours.Strength of 049 alloy increases after thermal exposure at 175℃ and 190℃for 24 hours,is same as that in T6 condition after thermal exposure for 36 hours,then decreases,decrease always after thermal exposure at 190℃ with increase in time.Strength of the alloy3 containing La without Ag decreases always after thermal exposure at 160℃,175℃ and 190℃with increase in time.(3)Strengths of the alloy3 containing La without Ag are 591.91 MPa and 616.62MPa in T6 and T8 respectively,are 532.62MPa after thermal exposure at 190℃ for 36 hours,which satisfied the requirements of oil drilling pipes,and saved production cost.(4)The dentritic structures in the ingots of 7055 alloy can be refined when some rare earth elements were added.(5)Strengths peak of 7055 alloy,the alloy containing Ag,the alloy containing Yb,the alloy containing Ce,the alloy containing La,the alloy containing Y and the alloy containing Pr are 691.68MPa、684.74MPa、711.12MPa、711.32MPa、697.81MPa、696.15MPa and 682.43MPa respectively when aging at 130 ℃.The hardening effect on 7055 alloy is Ce>Yb>La>Pr>Ag>Y.(6)Strengths of all alloys based 7055 studied in this paper decreased with increase in time when thermal exposure at 160℃.However,strengths of the alloys decreased slowly when thermal exposure at 160℃ for 36 hours and strength are higher than 537.42MPa when thermal exposure at 160℃ for 60 hours.