Study On Quenching Residual Stress Distribution And Reduction Process Of Aluminum Alloy Cylinder Head

Cylinder head is a complex casting in diesel engine.The reliability of the whole machine is directly affected by the structural reliability of the cylinder head.The cylinder head used in this paper is al-Si-Cu-Mg aluminum alloy,which belongs to heat treatment reinforced alloy.In order to obtain high saturation solid solution during heat treatment of cylinder head,it is necessary to carry out rapid quenching to make ?-Al phase in supersaturated state,and then carry out aging treatment to make precipitated phase disperse and improve the mechanical properties of cylinder head.Under normal circumstances,in order to make the performance of the cylinder head is achieved,the need to adopt high quenching speed,cylinder head has complex inner cavity structure,however,throughout its internal water system and the inlet and exhaust duct,the thick wall around 30 mm,and thin wall might be only 3-5 mm,so the cylinder cover during quenching,different parts of the cooling rate difference is bigger,It is easy to produce larger residual stress.And larger quenching residual stress in cylinder head causes deformation,or there is a larger residual stress,which results in the use process produce craze,eventually leading to the oil,gas leakage and leakage failure,failure resulting in cylinder head and cylinder head system considered the influence law of residual stress and the reliability of the method to eliminate residual stress is necessary.In this paper,aluminum alloy cylinder head is taken as the research object.Through the combination of simulation and experiment,the influence of coating coating on the residual stress of the corner of the cylinder head which is prone to cracking is studied,and the effect of thermal aging and vibration aging on reducing the residual stress of the whole cylinder head is studied.The specific research contents include the following parts:(1)Based on the inverse algorithm,the surface heat transfer coefficient of the cylinder head during quenching in water was obtained by fitting the simulated temperature curve and the temperature curve measured in the test.The temperature field and stress field of the cylinder head after quenching were determined by the Abaqus software simulation.From the simulation results,it can be found that the compression stress of the cooling part of the cylinder head and the tensile stress of the cooling part.This article adopts the method of coating paint,through changing the cooling order of each part of the cylinder head,influence the distribution of local residual stress,the experiment shows that the cylinder cover of airway wall corner after using coated paint outside the heat transfer coefficient,the area of the cooling rate increased,and for compressive residual stress after quenching,and this conclusion is verified by test,This provides a research method to solve the cracking problem of cylinder head.(2)According to the previous tests of the research group,the optimal aging process of the cylinder head is 170?/10 h.Therefore,under this condition,uniaxial tensile tests under165 MPa and 168 MPa stresses are carried out,and the relationship curve of creep strain with time is obtained.And calculated by the experimental data is deduced based on the ageing strengthening of constitutive equation,using the constitutive model of cylinder head cut,to simulate the process of residual stress and thermal aging results show that aging treatment can eliminate the residual stress of the cylinder head is about 30%,and compared with experimental data measured residual stresses,the accuracy of the model was verified.(3)Based on Abaqus software,a finite element model of cylinder head vibration aging process was established,and the modal analysis and harmonic response analysis of the cylinder head vibration aging process of the vibration force,vibration frequency and other parameters,and according to the simulation of the process parameters for the vibration aging experiment,the measured results show that residual stress The residual stress of cylinder head decreases by 30% ? 40% after vibration aging,which is consistent with the expectation.