Study On Plaster Investment Casting Technology Of Aluminum Alloy Thin-walled Parts

Aluminum alloy gypsum thin-walled parts,due to the relatively complex thin wall,structure and poor permeability of gypsum,it is easy to produce shrinkage and porosity,inclusions and other defects when casting,which limits their application.In view of the problems existing in ZL114A gypsum casting,the methods of computer simulation,microscopic observation?including metallographic microscope,scanning electron microscope?,phase analysis?X-ray diffraction?,energy spectrum analysis and mechanical properties testing were used.The effects of casting process,melt treatment and heat treatment on the microstructure and mechanical properties of aluminum alloy test rod and thin-walled parts were studied.The main results are as follows.?1?Through the computer simulation of the filling and solidification process of casting process,the reasonable design of the gating system can avoid the casting defects such as cold barrier,insufficient pouring,inclusion and solidification defects such as shrinkage hole and shrinkage porosity to some extent.In this experiment,the casting temperature is 720?and the mold temperature is 280?.Most of the shrinkage defects can be eliminated;?2?Through pouring test rods under different melt treatment processes?including unmodified+argon refining,modified+argon refining,argon refining+modified+argon refining?,the shrinkage and inclusion of the modified samples are obviously increased than that of the unmodified samples.The decrease of mechanical properties is related to the change of solidification mode and the reaction of modifier and melt;?3?The strengthening mechanism of T5 heat treatment rod without modified is obviously different from that of T5 heat treatment.Because the defects of shrinkage and porosity in as-cast unmodified samples are less,the improvement of mechanical properties of heat-treated specimens depends on whether or not thermal modification occurs during the Si phase,from needle-like to rod-like or granular;However,there are many shrinkage defects in the cast state of the modified sample,and the improvement of mechanical properties of the heat-treated specimen depends on whether the microstructure of the shrinkage edge can be strengthened during the heat treatment,and more Mg₂Si phases are precipitated by dispersion;?4?The effects of melt treatment,solidification pressure and liquid aluminum purification should be considered in the casting of aluminum alloy gypsum thin wall parts.The thin-walled plate specimen is precisely cast,the sample is modified and refined,the inclusion defect is more than that of the unmodified sample,and its mechanical properties are worse than that of the rod-shaped specimen under the same melt treatment condition.However,with the increase of solidification pressure?700KPa?and gypsum mold filter,the mechanical properties were improved obviously;?5?The T5 treatment is helpful to improve the sensitivity of shrinkage defects of the deteriorated sheet specimen.Before heat treatment,the edges of shrinkage organization are rough and on the edg,the eutectic Si and rich-iron phase that the shapes of them are coarse sheet or needle embed the?-Al inside which is easy to form thec source of crack because of the strong incision effect on the pinched wall.After T5 treatment,the egdes of shrinkage become smooth,the spherified eutectic silicon,the rounded iron-rich phase and the dispersed Mg₂S,All of them are helpful to slow down the crack nucleation and growth rate,thus greatly improving the mechanical properties of ZL114A alloy,Therefore,the mechanical properties of ZL114A alloy were significantly improved.