Effect of Cold Spray Parameters on Microstructure and Properties of 7050 High-strength Al Alloy Journal Box Body Coating
The 7050 high-strength Al alloys are easily to be cracked and the repair layers are easily oxidized and have much lower strength than the substrate materials when they are repaired with the thermal processing additive manufacturing technologies.To solve such problem,the work takes 7050 high-strength Al alloy journal box body used in high-speed train as an example and adopt cold spray,a low temperature solid-state material deposition process,to construct the repair layer.The 7050 aluminum alloy journal box body was used as the test material,with a specification of 100 mm×65 mm×10 mm.Before high-pressure cold spray,the surface of the test material was cleaned with acetone,and then sandblasted with 20 mesh Al2O3.Subsequently,by applying CS1,CS2,CS3 process parameters,the homogeneous powder was sprayed on the surface by high-pressure cold spray technology to prepare the sample.A DWCS-2000 cold spray system(Shaanxi Dewei Automation Equipment Co.,Ltd.,Xi'an,China)was used for coating deposition and it was equipped with a Laval nozzle with throat diameter of 2 mm,outlet diameter of 5 mm,and divergent section length of 180 mm.During the experiment,N2 was used for both the accelerating gas and powder feeding gas.An electric spark cutting machine was used to cut samples with size 20 mm×20 mm×10 mm,15 mm×15 mm×10 mm along the trajectory direction of the repair layer,and the cross section was polished.The surface morphology and cross-sectional microstructure of the repair layer were observed by Olympus DSX500 optical microscope and scanning electron microscope(SEM).A fine analysis of the interface structure was conducted by transmission electron microscopy(TEM).The microhardness of the repair layer and substrate was measured by microhardness tester(HVS-1000).The wear resistance of the repair layer and substrate was tested by ball and disc friction and wear testing machine(UMT-2MT).The corrosion resistance of the repair layer and the substrate was performed by electrochemical workstation(CS150H).The shear strength between the repair layer and the substrate was tested by the universal machine(WE-100).Results showed that the repair layer was compact with porosity less than 0.6%.With the increase of spraying pressure and spraying temperature,the porosity could be further reduced.The average hardness of the repair layer could reach 133.1HV0.05,slightly lower than the average hardness of the substrate(165.6HV0.05).The wear resistance of the repair layer was almost comparable with that of the substrate,for both the repair layer and the substrate and plastic ploughing governed the mass loss in wear test.The shear strength of the repair layer with the substrate was as high as 96 MPa.The electrochemical corrosion test indicated that the corrosion potential of the repair layer(-0.77 V,vs.SCE)was only slightly lower than that of the substrate(-0.70 V,vs.SCE),which suggested that galvanic corrosion between the repaired area and the original region could be avoided.The repair layer with dense structure,good adhension and equivalent performance to the substrate was prepared by high-pressure cold spray technology at CS3 process parameter.The remanufactured repair of the damaged journal box body is completed by the CS3 process parameter.The bench test results show that the repair surface of the journal box body is intact,and no peeling and crack of the repair layer is found.The porosity of the repair layer is around 0.05%,meeting the requirements of service conditions.
国家科技期刊平台
NSTL
万方数据
