| Tube hydroforming is an advanced plastic forming technology which can realize the lightweight of parts structure and respond to the policy of energy saving and emission reduction and sustainable development.Its products not only guarantee high quality and precision,but also have the advantages of light weight and high strength.But the tube hydroforming technology must rely on high-performance special external pressure source,and the equipment cost is high,at the same time,the forming efficiency is affected by the long period of pressure-increasing and pressure-releasing.Liquid impact forming is an advanced manufacturing technology developed on the basis of tube hydroforming technology and stamping forming technology.This technology not only retains the advantages of tube hydroforming,but also improves the forming efficiency,which has broad application prospect and research value.Meanwhile,the heat treatment process has a close influence on the mechanical properties,forming properties and microstructure of materials.Therefore,this paper studies the influence of heat treatment process on the properties and microstructure of H65 brass and 6061 aluminum alloy tubes based on liquid impact forming technology,hoping to provide a useful reference for the study of liquid impact forming technology.The mechanical properties of H65 brass and 6061 aluminium alloy tubes under different heat treatment conditions were tested by tensile test at room temperature,and the variation laws of mechanical property parameters with heat treatment process parameters were analyzed and summarized.The plastic constitutive models of H65 brass and 6061 aluminum alloy tubes under different heat treatment processes were established based on power exponential hardening model.When annealing temperature is 450℃ and holding time is 60 min,H65 brass tube has lower yield ratio and higher strain hardening index,which is more beneficial to plastic deformation of the material,and its elongation reaches76.7%.When the heat treatment temperature is 550℃,the holding time is 120 min,and the cooling method is air cooling,the 6061 aluminum alloy tube has higher strain hardening index,lower yield ratio,better mechanical properties,and the elongation is 26.1%.Based on the liquid impact forming technology,the bulging tests of H65 brass and6061 aluminium alloy tubes in heat treatment state were completed,and the liquid impact forming parameters of different heat treatment states were collected.The variation laws of bulging properties such as bulging height and wall thickness distribution in natural bulging area and filling properties such as bulging height,fillet radius and wall thickness distribution in die closing area were summarized under different heat treatment processes.When the annealing temperature is 450°C and the holding time is 60 min,the H65 brass has better formability.The bulging height of the natural bulging area reaches 55.82 mm,which is increased by 47%,and the wall thickness distribution is uniform.Considering cost,efficiency and other factors,heat treatment temperature of 550℃,holding time of 120 min,and cooling mode of air cooling are more reasonable heat treatment process of 6061 aluminum alloy tubes.The bulging height of the natural bulging zone is 46.26 mm,which increases by about 22%.The microstructure and fracture morphology of H65 brass and 6061 aluminum alloy were analyzed by means of optical microscope and scanning electron microscope.With the increase of temperature,the initial grain size of the material becomes finer,the number and depth of dimples on the surface of the fracture surface of the formed part increase,and the microstructure change is not obvious under different holding time.As a result of plastic deformation,the grains in each sampling location are broken and refined to different degrees.The grains in the natural bulging region tend to be elongated along the plastic deformation direction,and the grains have obvious orientation. |
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