Study On The Ultra-high Cycle Fatigue Performance Of Laser Remanufacturing Of 2A60 Aluminum Alloy

Compressor is an important part of aero engine.In the process of aircraft operation,due to the uneven distribution of airflow,instability and other reasons,will cause the compressor impeller blade periodic excitation,the impeller blades are in the process of running under high frequency,low stress and small strain cyclic loading.Since the service life of the aero-engine is around 2000 hours,the alternating load of the impeller blade of the compressor will be more than 10~9 weeks,thus entering the ultra-high cycle fatigue stage.In addition,the impeller is usually made by means of overall machining,and the failure of a single blade causes the entire impeller to be scrapped.Therefore,it is necessary to explore the high cycle fatigue performance and remanufacturing process of impeller material.In this paper,the ultrasonic fatigue test system is used to carry out ultra high cycle fatigue test for aero-engine compressor material 2A60 aluminum alloy samples.Through the S-N curve and fracture morphology,its ultrahigh cycle fatigue characteristics were analyzed.At the same time,laser welding and laser shock method were used to produce the ultra-high cycle fatigue test after remanufacturing,and then carry out the ultra high cycle fatigue test.The effect of remanufacturing technology on the fatigue properties of impeller material was investigated by comparison of s-n curve,residual stress and roughness.The final results show that:(1)The ultra-high cycle performance of 2A60 aluminum alloy after laser welding is significantly lower than that of substrate,and its s-n curve is continuously decreasing,and there is no fatigue limit.The fatigue life of samples with poor welding combining state will not more than 3×106,The fatigue life of samples with good welding combining state decreased by 35%or more compared with base material,but the fracture morphology is similar to the base material.(2)The laser welding process introduced the residual tensile stress near 200 MPa on the sample surface,and the residual tensile stress decreased gradually with the increase of depth.The residual tensile stress on the sample surface is very unfavorable to the ultra-high cycle fatigue performance of the sample,which can reduce the fatigue threshold value on the sample surface,thus causing the fatigue crack to appear on the sample surface in advance.(3)Laser shock can improve the negative effect of laser welding on fatigue performance of 2A60 aluminum alloy.After the laser shock,the maximum stress value of the sample can be increased to 160 MPa from 140 MPa after welding.However,the S-N curve of the sample after the laser shock is still falling,there is no fatigue limit,and there is still a certain gap between the fatigue performance of the base material.(4)The residual compressive stress of nearly 500 MPa was introduced on the surface of 2A60 aluminum alloy during laser shock.The residual compressive stress can be offset with alternating load part of the tensile stress,thereby,thus to reduce the average stress level,improve the crack initiation threshold values,reduce the speed of the crack initiation and propagation,which is the main reason why the laser shock improves the fatigue properties of aluminum alloy samples.In addition,the surface roughness of the sample surface after the laser shock was reduced from 0.928?m to 0.822?m,and the surface fatigue threshold of the smooth sample surface was higher,which is another reason for the laser shock to improve the fatigue performance of aluminum alloy.