Effect Of Cryogenic And Laser Shock On Microstructure And Thermal Fatigue Properties Of Aluminum Bronze Alloy

Aluminum bronze has excellent comprehensive mechanical properties.And it is an indispensable material in modern industry which is widely used in aerospace,ocean,petroleum and petrochemical industries and other engineering machinery.With the development of modern industry,aluminum bronze parts are prone to thermal fatigue damage when they operate steadily under heavy load,corrosive medium and high cyclic stress conditions,start-up,shutdown or abrupt change of working conditions.Thermal fatigue is a complex process of mechanical damage and tissue degeneration.Generally,no obvious plastic deformation occurs.Therefore,it is difficult to detect and prevent with great potential danger.Once an accident occurs,it is often catastrophic.How to improve the thermal fatigue properties of aluminum bronze alloys to meet the application needs of high-tech fields,this problem needs to be solved urgently.Based on this,the effects of solution aging,cryogenic treatment,laser shock treatment and combination on the microstructures,mechanical properties and thermal fatigue behavior of ZCuAl₁₀Fe₃Mn₂ alloy at room temperature to 450?were studied.The mechanical properties,microstructures and surface morphologies of the alloy were observed by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,energy dispersive spectrometer?EDS?,optical microscopy?OM?,atomic force microscope and basic mechanical testing methods,and the changing rules and strengthening mechanism were analyzed.The thermal fatigue properties of the alloys strengthened by different processes were tested by LRS 1200 thermal fatigue tester to observe rules of initiation and propagation of thermal fatigue cracks and analyze the strengthening mechanism of thermal fatigue resistance.The following conclusions are obtained through research:?1?The mechanical properties and microstructures of ZCuAl₁₀Fe₃Mn₂ alloy can be remarkably improved by?950+5??×1 h solid solution treatment+?350+5??×1 h aging treatment+cryogenic?2h?composite treatment.Compared with T6 treatment,the tensile strength,hardness and elongation of the alloy increased by 7.28%,16.96%and 23.53%respectively,and its alpha phase is further refined and distributed more uniformly,and dislocation density increased,which make the overall structure uniformity and compactness of the alloy better.The thermal fatigue properties of the alloys are improved by improving the comprehensive properties,and the thermal stress resistance and oxidation corrosion resistance of the alloys are enhanced.Compared with as-cast,T6 and cryogenic alloys,the fatigue crack length is the shortest and the crack growth rate is the slowest under the same number of cold and hot cycles.?2?The thermal fatigue properties of ZCuAl₁₀Fe₃Mn₂ alloy can be significantly improved by laser shock with a spot diameter of 3.0 mm,a lap rate of 50%,and an energy of 4 J.Compared with as-cast alloys,the surface roughness of laser shock strengthened alloys increases by 17.88%and-268.5 MPa residual compressive stress occurs at the same time.The dislocation increases greatly,the grain size of alloys is refined remarkably.The hardness of the alloys is increased by38.88%due to the precipitation of beta phase and iron-rich kappa phase from alpha phase.Under the above factors,the oxidation resistance and thermal fatigue resistance of the alloys are enhanced remarkably.When the thermal fatigue crack propagates to the laser shock hardening zone,the crack tip closure does not propagate forward.?3?After cryogenic treatment,laser shock and its combination treatment:1)The density of the alloy structure is increased,the defects such as holes are reduced,the sharp corners of the grains are passivated,and the source of crack initiation is reduced,so that the crack initiation resistance of the alloy is increased;2)the dislocation of high density is generated,the grain size is refined,the high temperature oxidation resistance is enhanced,so thermal fatigue crack growth is hindered.3)Residual compressive stress counteracts the tensile stress generated during the cycling process.Reducing the total thermal stress and improving the thermal fatigue crack initiation resistance of ZCuAl₁₀Fe₃Mn₂ alloy.