| Most of the connecting rods of general gasoline engine are made of Al-Si-Mg6061 aluminum alloy.At present,pressure casting or ordinary hot die forging is widely used to manufacture the connecting rod of general gasoline engine.There are many production processes,long technological process,low material utilization rate and high production cost.In this paper,6061 aluminum alloy connecting rod forgings are taken as the research object,and the precision connecting rod forgings are obtained by closed-die forging.By studying the evolution of flow stress and microstructure during hot deformation of 6061 aluminum alloy,the optimum technological parameters of 6061 aluminum alloy hot deformation are obtained.The flow law of two typical aluminum alloy connecting rods in closed-die forging is investigated and analyzed,the reasonable forming process scheme and solid solution treatment method are worked out,and the technological problems of precision forming aluminum alloy connecting rod are analyzed and solved.The influence of different process parameters on the thermal compression and deformation of 6061 aluminum alloy is analyzed by a Gleeble-3500 thermal simulation compression testing machine.The 6061 aluminum alloy has a positive strain rate sensitivity,with the increase of the strain rate,the peak rheological stress and the peak strain of the alloy are increased,and with the increase of the deformation temperature,The peak rheological stress and the peak strain of the alloy are reduced.The deformation activation energy of 6061 aluminum alloy is 236.252k J/mol,and the constitutive equation of the rheological stress of the alloy is established, ε=2.6×1017sinh（0.0151σ）8.93 exp（-236.252/8.414T）.Based on the dynamic material model（DMM）,the processing map of 6061 aluminum alloy under different strain is established.The optimum forming temperature and strain rate of6061 aluminum alloy are 440～470℃and0.1～1s-1.Based on the results of thermal compression test,the dynamic recrystallization model of 6061 aluminum alloy including peak strain equation,critical strain equation,dynamic recrystallization kinetic equation and dynamic recrystallization grain size equation was obtained by linear regression method.The effect of strain rate and deformation temperature on the dynamic recrystallization of the alloy is obtained by finite element numerical simulation of thermal compression process.with the increase of deformation temperature,the dislocation density of 6061 aluminum alloy after deformation decreases and the dynamic recrystallization grain size increases;the decrease of strain rate is beneficial to the occurrence of dynamic recrystallization,and the recrystallization grain size increases.Based on the Constitutive relation and Microstructure Mathematical Model of6061 Aluminum Alloy,the metal flow law,velocity field,stress-strain field and dynamic crystallization in block forging of aluminum alloy connecting rod with different structural forms were analyzed by using finite element simulation software DEFORM.Through the analysis,for the integral aluminum alloy connecting rod,the punch bidirectional synchronous block extrusion forming,and for the split aluminum alloy connecting rod,the punch three-way asynchronous block extrusion forming,the formed connecting rod is full and has no obvious defects.Taking the typical split aluminum alloy connecting rod as the forming object,the forming process parameters of closed-die forging are optimized and analyzed.The optimum forming temperature is 450℃,the deformation speed is 12 mm/s,and the friction coefficient is 0.2.With the help of the special die base and process equipment for closed-die forging,the three-way closed-die forging process test of aluminum alloy connecting rod was completed.The effects of solution and aging treatment on the microstructure and properties of 6061 aluminum alloy connecting rod were studied.The optimum solution temperature of 6061 aluminum alloy connecting rod was 530℃,the time was 100 min,the aging temperature was 175℃,and the time was 300 min.finally,the precision forgings of aluminum alloy connecting rod with good quality were developed. |
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