| The aluminum alloy itself has poor wear resistance,corrosion resistance,and electrical insulation,which limits its wide application in the aviation industry.Micro-arc oxidation technology is a green and environmentally friendly surface treatment process that enables a non-ferrous metal surface to grow a ceramic film,which can significantly improve the overall performance of the metal surface.However,due to microscopic defects in the micro-arc oxidation ceramic layer,the fatigue performance of the metal matrix may be reduced.The fatigue performance of metallic materials is an important reference data for structural design.Therefore,it is necessary to develop the micro-arc oxidation ceramic layer to study the fatigue properties of aluminum alloys.The main research work is as follows:(1)Coatings were deposited on the surface of 2024 and 7075 bare aluminum alloy by micro-arc oxidation and the oxide film was tested.This paper selected different process parameters including pulse duty cycle,micro-arc oxidation pretreatment substrate surface roughness and oxidation time to fabricate coating on the surface of 2024-T3 and 7075-T6 aluminum alloy.Using eddy current thickness gauge,scanning electron microscope,X-ray diffraction and 3D laser confocal microscopy analyses the thickness of the ceramic layer,the surface of the ceramic layer and the interface between the ceramic layer and the substrate,the oxide composition of the ceramic layer,and the three-dimensional morphology of the surface.(2)Fatigue testing and data processing.The fatigue test of 2024 and 7075 bare aluminum,aluminum clad,and coated samples with different micro-arc oxidation process parameters were performed.The least squares method was used to fit the test data,and the material constants(k and Cs)and S-N curves of aluminum alloy under different conditions were obtained.(3)The influence of different micro-arc oxidation processes on the fatigue life was investigated.Under high and low cyclic fatigue conditions,the fatigue life of 2024 and 7075 aluminum alloys and coated aluminum alloy specimens was analyzed.It is based on the test results of the micro-arc oxidation ceramic layer with different pulse duty cycles,substrate surface roughness,and micro-arc oxidation time.(4)A fatigue life prediction model for aluminum alloys and coated samples with different substrate surface roughnesses was established.Based on the fitting fatigue test data,the dislocation model and fatigue fracture theory,the fatigue life prediction model of aluminum alloy and different substrate surface roughness coating specimens was established.Based on the above research work,the fatigue performance of the coated aluminum alloy is better at the duty cycle of 10%.Under the conditions of high and low cycle fatigue,the different substrate surface roughness has different effects on the fatigue life of the coating sample,and in the 50 minute oxidation time,the fatigue life appears to increase first and then decrease.The results provide a theoretical reference for the application of micro-arc oxidation technology in production practice.Moreover,the existing fatigue life model is applied to coated specimens.The fatigue life prediction provides an effective basis for the structural design of micro-arc oxidation coating aluminum alloy. |
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