Study On Rheological Die Casting Simulation And Forming Process Of A356 Aluminum Alloy Air Compressor Bracket

In recent years,"carbon peak" and "carbon neutrality" have become a hot topic.Automobile lightweight is the most effective measure to reduce carbon emissions in the automobile industry.Aluminum alloy pressure casting technology can achieve automotive lightweight in a short time.At the same time,aluminum alloy die casting is a feasible technology which can be produced commercially in large quantities.Under the requirement of "dual carbon" goal and automobile lightweight,aluminum alloy die casting will become the research hotspot in the future.But because the high pressure die casting has the forming characteristics of "high pressure and high speed",the metal liquid is sprayed into the cavity.And it is easy for liquid metal to entrap,during the filling process of liquid metal.Defects such as shrinkage cavity and porosity are easy to occur after casting solidification.The viscosity of semi-solid slurry is better than that of liquid metal.In the semisolid slurry filling process,the semi-solid slurry is relatively stable,the slurry will not occur enrolling phenomenon.So there are almost no internal defects in semi-solid die casting.Semi-solid die casting is an ideal process for producing high quality aluminum alloy castings because of its simplicity,less defects and heat treatment.This paper takes the support of air compressor as the research object.And the molding method used is semi-solid die casting.Firstly,prefabricated A356 metal blocks were stirred into A356 melt to prepare semi-solid slurry.The influence of stirring temperature and stirring speed on the semi-solid slurry was studied.Through the observation of the microstructure of the semisolid,the best preparation technology of the slurry was selected.Secondly,this paper uses Anycasting software to analyze the mold flow in the die casting process.Through the analysis of the filling process and solidification process,the influences of the primary and secondary fast injection rates on semi-solid die casting can be explored.We can get the best die casting process.Finally,the semi-solid slurry is die-cast under the best technology.The differences of defects,microstructure and mechanical properties between semi-solid die casting and high pressure die casting were analyzed.In this paper,the optical microscope was used to observe the microstructure.The Xray flaw detector was used to detect the casting defects.The Vickers hardness tester and the universal tensile testing machine were used to test the mechanical properties of the casting.And the scanning electron microscope was used to observe the fracture morphology.The following conclusions are reached:With the increase of stirring temperature,the grain size of primary solidification structure and secondary solidification structure decreased first and then increased,and the shape factor of primary solidification structure and secondary solidification structure increased first and then decreased.When the stirring temperature is 680℃,the microstructure of semi-solid slurry is the best.With the increase of stirring speed,the grain size of primary solidification structure and secondary solidification structure decreased first and then increased,and the shape factor of primary solidification structure and secondary solidification structure increased first and then decreased.When the stirring speed was 1000r/min,the microstructure of semi-solid slurry was the best.The optimum pulping process of semi-solid slurry is as follows: stirring temperature is 680℃,stirring speed is 1000r/min.Under the optimal slurry preparation technology,the minimum grain size and the maximum shape factor of the single solidification structure are 69.00μm and0.73 respectively.The minimum grain size of secondary solidification microstructure is 25.54μm and the maximum shape factor is 0.64.The software Anycasting was used to analyze the die flow in the die casting process.It is found that the semi-solid slurry filling is stable in the process of die casting,which can effectively improve the phenomenon of gas rolling in liquid metal die casting.The semi-solid die casting process can avoid the defects such as shrinkage porosity and shrinkage cavity.The optimal process parameters of semi-solid die casting are as follows: the first fast injection rate is 1.5m/s,and the second fast injection rate is 3.5m/s.When a fast injection is too slow,the semi-solid slurry can not be completely filled,we can not get a complete casting.When the secondary fast injection is too slow,the solid phase appears in the filling process,resulting in cold isolation and other defects.When the secondary fast injection is too fast,the slurry filling is not stable and gas rolling occurs.High-pressure die casting and semi-solid die casting were used to shape the air engine support.It is found that the high pressure die casting has obvious defects at the far gate,thick wall and near the gate,while the semi-solid die casting has almost no defects inside.The structure of high pressure die casting is dominated by dendrites.The semi-solid die casting α-Al has a near-spherical morphology,the minimum grain size of the semi-solid structure is 44.00μm,and the maximum shape factor is 0.85.There is almost no difference in tensile properties between high-pressure die casting and semi-solid die casting near the gate,and the tensile strength is about 230 MPa.The tensile strength of the high pressure die casting is 157 MPa at the far gate,and the tensile strength of the semi-solid die casting is 190 MPa.The tensile property of the semi-solid die casting is obviously better than that of the high pressure die casting.