Study On Defections And Heat Treatment Of The Cylinder Of Vacuum Die-casting Aluminum Alloy

Die casting is widely used in the manufacturing of complex automobile parts,such as engine cylinder block,cylinder head,manufacturing,but easy to entrap gas.However,vacuum die casting is an effective measure to solve this question,not only reducing the number of pores,and reducing pore size at the same time.So far,the effect of vacuum degree on casting organization,performance and related research is relatively few.Based on a certain engine cylinder produced by vacuum die casting engine cylinder as the experimental object,the defects of cylinder wall on machined surface location A,B,C,D,E conduct section,and by using experiment means of SEM,EDS and metallographic observation,the defects on the surface of the cylinder wall machining is studied.And in a metallographic microscope the skin layer of cylinder wall is observed.at the same time,the effect of T5 heat treatment on the mechanical behavior and microporous is studied by density measurement and tensile experiments respectively.The following conclusions are drawn in the end.(1)The results of defect sections on machined part surface location A,B,C,D,E show that the defect of location B is mainly pore and shrinkage cavity,where the size of typical pores is 169 ?m and 128 ?m respectively,But in location D,the type of defect is shrinkage and hot cracks.In addition,the other research locations of the cylinder block are a plate-like defect.(2)The energy spectrum analysis(EDS)results show that the element of inclusions in some plate-like defects is mainly C and O,and it is analyzed that the introduction of inclusions can be resulted from release agent and lubricant between the punch and pressure chamber.(3)The outermost surface of skin layer in this research is a relatively small Al-Si eutectic organization,followed outermost surface being a small white ?-Al layer,further followed being a more coarse Al-Si eutectic organization than most outer layer.Moreover,the thickness of surface layer in this study is ~250 ?m.(4)Through comparing the changes of hole morphology in specimens between before and after T5 heat treatment(210 ?+3 h),it is found that the porosity defects with high roundness have the tendency to be a long strip defect.(5)By measuring the density of the T5 samples before and after heat treatment,the change of porosity in the sample is studied.The results represent that sample density before T5 heat treatment is 2.70 g/cm3 and that after T5 heat treatment is 2.63 g/cm3,decreasing by 2.66 %.For the porosity increased from 2.03 % before the heat treatment to 4.64 % after the T5 heat treatment,it increases double,which represents that T5 heat treatment make micro-porosity grew up double in a sample.(6)The three groups tensile experimental results before and after T5 heat treatment show that the ultimate tensile strength of the 1st and 3st group is reduced after T5 heat treatment,but the ultimate tensile strength of the second group after T5 heat treatment is a smaller increase.It is analyzed that the expansion of micro-pores plays a major role in the 1st and 3st group experiment,and the second phase of aging precipitation plays a main role in the 2st group experiment.