Study On Microstructure And Properties Of QAl9-4 Alloy For Catenary Of Electrified Railway

As one of the commonly used materials in the production of high-speed railway catenary components, QAl9-4 alloy is a kind of multi aluminum bronze, has good mechanical properties, good wear resistance, corrosion resistance, and excellent electrical conductivity,thermal conductivity. With the rapid development of rail transport industry, the service performance of the QAl9-4 alloy catenary components is put forward. This paper takes the QAl9-4 alloy containing 9.4%~10.0%Al as the study object. The effects of solid solution aging treatment process and stabilizing annealing treatment process on the microstructure and properties of extrusion R state, extrusion and tension Y state QAl9-4 alloy after upsetting deformation were studied by tensile properties test at room temperature, hardness test,microstructure and fracture scanning, etc. And the best heat treatment process of R state and Y state QAl9-4 alloy was obtained to meet the requirement of the use of contact network parts. The results show that:1)The optimal heat treatment process of R and Y state alloy is solution at 910℃ for 1h and then aging at 550℃ for 5h. After using this process, the alloy has good comprehensive mechanical properties. The tensile strength, yield strength, hardness and elongation of R state QAl9-4 alloy are 657MPa、298MPa、172.5HB、26% respectively, which are improved by10.2%、15.1%、5.0%、19.3% respectively compared with those of the specimen after upsetting deformation. While these of Y state QAl9-4 alloy are 662MPa、305MPa、171.8HB、25.2%respectively, which are improved by 6.9%、13.0%、2.0%、33.3% respectively compared with those of the specimen after upsetting deformation.2) R state and Y state QAl9-4 alloy have the same solution and aging strengthening mechanism, which was that β solution and supersaturated α solution were acquired after the alloy was hold at appropriate temperature for a certain time, then metastable martensitic β’phase and supersaturated α solution were acquired after quenching, and then small granular k phase was obtained from decomposition of metastable martensitic β’ phase and supersaturatedα solution during aging treatment, so that the alloy has better comprehensive performance.3)Properties and microstructure of R and Y state QAl9-4 alloy can be improved by proper annealing process. After annealing treatment at 700℃ for 2 hours, the tensile strength, yield strength, elongation and hardness of R state QAl9-4 alloy are 611MPa、276MPa、29.1%、164.7HB respectively, which are improved by 2.5% 、 6.6% 、 33.5%、 0.2% respectively compared with those of the specimen before heat treatment. After annealing treatment at700℃ for 2.5 hours, the tensile strength, yield strength, elongation and hardness of Y state QAl9-4 alloy are 644MPa、289MPa、26.3%、170.3HB respectively, which are improved by4.0%、7.0%、39.2%、0.9% respectively compared with those of the specimen before heat treatment.4)After annealing treatment, the small(α+γ2)eutectoid was uniformly distributed among the αphase, a certain amount of k phase uniformly dispersed in the organization, which makes the alloy with high plasticity, strength, hardness.5)After annealing treatment at 700℃ for 2.5 hours, cable terminal anchoring wire clamp produced by Y state QAl9-4 alloy has uniform structure, the hard and brittle of(α+γ2)eutectoid was uniformly distributed among the α phase, a small amount of granular k phase uniformly dispersed in the organization, the tensile strength, yield strength, elongation and hardness reaches 634MPa、301MPa、28.2%、169.4HB respectively. After solid solution aging treatment which was heat preservation at 910℃ for 1 hour then water cooling was carried out, and heat preservation at 550℃ for 5 hours then air cooling was carried out, the microstructure of contact wire terminal anchoring wire clamp produced by R state QAl9-4alloy retains the β’ martensitic uniform distribution with uniformly dispersed granular k phase.With adopting the process, the R state QAl9-4 alloy achieved well combination of strength and plasticity, of which he tensile strength was 678 MPa, yield strength was 319 MPa,elongation was 24.9% and hardness was173.8HB.