Study On Defect Control Of Aluminum Alloy Die Casting Forming

Due to advantages of low density,high strength,good molding performance and corrosion resistance,aluminum alloy has been widely used in automobile,construction,aviation,aerospace and other fields.Die casting is one of the main forming methods of aluminum alloy structural parts,but due to the defects such as porosity and shrinkage porosity,aluminum alloy die casting is often scrapped.Besides,due to the porosity defect,the casting can not be further improved by heat treatment,which limits its application.In this paper,the causes and prevention of porosity and shrinkage defects in aluminum alloy natural gas regulating valve cover were studied.The main research methods,contents and results are as follows:(1)In this study,according to the characteristics of ZL104 alloy and the valve cover,the mold gate area was determined 54.05mm~2,with the filling speed of 34.4m/s,the casting temperature of 650℃,and the mold temperature of 200℃under the traditional die casting process and mold design method combined with PQ~2 figure.The numerical simulation analysis using AnyCasting software shown the rapid filling speed of the alloy liquid particularly turbulent flow phenomenon,with a large amount of air volume.The solidification sequence is not reasonable,and there are more isolated liquid regions in the mold cavity at the later stage of solidification,resulting in more pores and shrinkage cavity defects.(2)Under the condition that the main structure of the die casting machine and die casting mold remains unchanged,the Indirect Squeeze-Casting molding process is formed with extrusion casting,and the area of inner gate is measured as 540.5mm~2.The orthogonal experiment with three factors and three levels of mold filling speed,casting temperature and mold temperature was conducted.The results reveal that the alloy liquid filling was stable and no obvious turbulence appeared,the air volume during the filling process was significantly reduced,the feeding channel was unimpeded and no isolated liquid phase zone appeared,and the porosity and porosity defects in the casting were basically eliminated,when the filling speed,casting temperature and mold temperature were 1m/s,640℃and 190℃respectively.(3)Indirect Squeeze-casting valve has no deformation,bulging or cracking,after the valve was treated with solid solution at 535℃for 3h and aged at 175℃for 5h.It is shown that the porosity defect in the casting is controlled and the heat treatment performance is good(4)The Brinell hardness of the die-cast valve cover,the indirect extrusion valve cover and the indirect extrusion valve cover after heat treatment were measured as 59.95,78.49 and96.46 respectively,whereas the tensile strengths 140MPa,192MPa and 257MPa correspondingly.After process optimization and heat treatment,the mechanical properties of the valve cover are improved significantly.(5)By means of direct reading spectrometer,XRD,OM,SEM and EDS,it is found that the main reasons for the increase of tensile strength and Brinell hardness of the Indirect Squeeze-Casting after heat treatment are as follows:Stomata are eliminated.The shrinkage cavity and porosity defects are reduced,the primary Si is passivated,and the sheet eutectic Si is fused and spheroidized.