Research On Integrated Control Technology Of Cast Aluminum-silicon Alloy Properties

In view of the property requirements of hypoeutectic ZL101 alloy and near-eutectic Al Si10Cu0.9Mg0.4 alloy,as well as the industrial demand of greener and leaner manufacturing process,this paper explores the method of reducing the defects heredity of recycled material and eliminat ing the tendency of pinhole defects after Sr modification in the casting process,and explore a new integrated control process of shortening the solution treatment time by using the waste heat of casting.Through the comparative study of different melt processing methods,different solution treatment on microstructure and mechanical properties,and by analyzing the variation trend and internal mechanism of the influence of eutectic Si phase,Mg₂Si phase and the third phase morphology characterization on mechanical properties,the conclusion was drawn that after aluminum liquid heat treatment,the best mechanical properties of aluminum alloy can be achieved by using the melt combined treatment of rare earth Ce compound refining and modification and by using the waste heat of casting to do solution treatment for 3h,then water quenching and artificial aging.It was successfully applied to CM50 flywheel shell product of heavy-duty diesel engine,and an intelligent production line was built.The relationship between key process parameters and product property and dimensional accuracy was studied,and the optima l process parameters were determined,which improved production efficiency and quality stability.The main research results are as follows:The slight change of thermal effect between 862℃and 886℃corresponds to the melt structure transformationof ZL101 alloy.In this paper,theα-Al dendrites in ZL101 alloy changed from coarse dendritic to equiaxed,the number of secondary dendrites decreases obviously.The eutectic Si phase distributes aroundα-Al grain and transforms from needle-like to granular.When the content of Ce reaches 0.45%,the microstructure of ZL101 alloy is improved and the shape ofα-Al dendrites changes from coarse dendrite to equiaxed dendrite.The as-cast strength and elongation of ZL101 alloy after heat rate treatment increased by 5.6%-6.7%.With the increase of Ce addition in melt composite treatment,the tensile strength and yield strength of ZL101 alloy increased firstly and then decreased.When the addition content of Ce was 0.4%,the mechanical properties of ZL101 alloy reached the maximum value.The tensile strength and yield strength were 183 MPa and 124MPa respectively.By observing the microstructure of Al Si10Cu0.9Mg0.4 and ZL101 treated by integrated heat treatment,it is found that theα-Al phase morphology of the primary crystal is similar to that of T6 treatment.The average particle size of Al Si10Cu0.9Mg0.4 is 3.3μm after integrated heat treatment,while that of T6treatment is 4.0μm,and the morphology is fibrous.The average size of ZL101 after integrated heat treatment is about 5.3μm,while the average size of T6 treatment is around 4.5μm,and the morphology is flake and coral,respectively.At the same time,the Mg₂Si phase grows at the grain boundar y and basically adheres to eutectic Si.The number of Mg₂Si phase after integrated heat treatment is more than that after T6 treatment.In addition,the distribution of Mg₂Si is more uniform and the morphology is more round.After integrated heat treatment,Q-Al₅Cu₂Mg₈Si₆precipitates appear at the grain boundary of Al Si10Cu0.9Mg0.4 alloy in the form of coarse blocks and plates.The morphology improving of eutectic Si phase and Mg₂Si phase is the main reason for the increase of tensile strength and elongation.Al Si10Cu0.9Mg0.4 alloy adopted the sta ndard T6 heat treatment,T6-3h with50%solution time shortened and the integrated heat treatment which shortened the solution time by 50%by casting waste heat treatment respectively.The results show that the tensile strength and yield strength of the integrated heat treatment are equivalent to the standard T6,the elongation is about 60%lower than T6.The tensile strength and elongation of T6-3h process,which directly shorts 50%of solution time,are obviously lower than that of integrated process.The experimental results of ZL101 are basically consistent with Al Si10Cu0.9Mg0.4.Theα-Al grains of ZL101 alloy were very fine and the eutectic Si was short-rod or spherical after melt combined treatment and integrat ed heat treatment.With the increase of Ce addition content in melt combined treatment,most of eutectic Si changes from short-rod shape to spherical shape.The eutectic Si with good spheroidizing effect was 2-5μm and distributed uniformly on the matrix.When the content of Ce reached 0.45%,the eutectic Si tended to become spherical.The tensile strength and yield strength of ZL101 alloy after integrated heat treatment were 308 MPa and 232 MPa respectively,which were 2.3%and 2.2%higher than those of ZL101 alloy without heat rate treatment.When the content of Ce reached 0.4%,the mechanical properties of ZL101 alloy had the maximum value.The tensile strength and yield strength were 322 MPa and 241 MPa respectively.In addition,the fracture belonged to the mixed fracture.When the content of Ce was0.5%,the fracture was brittle fracture.After the integrated heat treatment of ZL101alloy with 0.2%Ce melt combined treatment,the tensile strength and yield strength of the sample increased by 4.3%and 3.5%compared with the T6 treatment,and the elongation remained the same.By optimizing the process parameters of melting,casting and integrated heat treatment,the research results are applied to CM50 flywheel housing of heavy diesel engine.The tensile strength of ontology sampling is greater than 290 MPa,the yield strength is greater than 230 MPa and elongation is greater than 4.0%,which make 29%energy saving of heat treatment realized during mass production.