Study On Process Optimization And Microstructure Properties Of Die Castings For Thin-walled Magnesium Alloys

This subject takes the AE44 magnesium alloy radar shell die casting as the research object.Because the radar shell occupies an important position in the entire radar system,its quality directly affects the sensitivity of signal detection.The use of AE44rare earth magnesium alloy plays a role in weight reduction,while its excellent strength and toughness can well meet the requirements of radar enclosure work.The topic seeks the optimal die casting process for radar enclosures by combining numerical simulations with experimental research and verification to obtain radar enclosures of good quality.Three kinds of pouring schemes were designed from the shape and size of the radar enclosure.After analyzing the filling process of each solution,the casting scheme with an inner runner cross-section of 1446 mm² was finally selected.The inner shrinkage cavity of the casting has been effectively reduced after the overflow system was added.The volume content of shrinkage was effectively reduced.The total content was 0.2143 cubic centimeter,which was about 50%of that before the addition.The orthogonal test was conducted by selecting the influencing factors of pouring temperature,mold temperature and injection speed.The experimental results show that when the pouring temperature is 680°C,the mold temperature is 180°C,and the injection speed is 3.5 m/s,the volume content of the defect inside the casting is the lowest,which is 0.1982 cubic centimeter.It is further reduced by 7.5%based on the addition of the overflow system.The mechanical properties and microstructure of the casting bulk specimen were tested and observed.The test results show that:when the pouring temperature is increased from 660°C to 680°C,the dendrites in the structure gradually decrease,the crystal grains become even and round,and the mechanical properties are improved.When the temperature exceeds 680°C,severe shrinkage occurs in the structure,and the mechanical properties also decrease.When mold temperature is in the range of180°C to 200°C,a chilled layer is formed on the surface of the casting,and the microstructure is a surface fine grained zone,and the mechanical properties are good.At 180°C,the hardness reaches a maximum of 81.3 HB.When the temperature exceeds 200°C,the chilling effect decreases,the hardness decreases,and the mechanical properties also decrease.When the injection speed rises from 3.0 m/s to3.5 m/s,both the tissue density and mechanical properties are significantly improved.When the injection speed is further increased,the air-jaw phenomenon is serious,the porosity is increased,and the quality of the casting is deteriorated.It is concluded that When the pouring temperature is 680°C,the mold temperature is 200°C,and the injection speed is 3.5 m/s,the microstructure and properties of the casting are optimal.Under this parameter,the tensile strength was 245 MPa,the elongation was 5.48%,and the Brinell hardness was 79.6 HB.The best process parameters obtained by numerical simulation and experimental research were compared and verified.The results show that the internal shrinkage shrinkage volume of the casting is 0.1736 cubic centimeter under the best experimental parameters,which is better than the simulation results.The content decreased by 12.4%.Finally,when the pouring temperature is 680°C,the mold temperature is 200°C,and the injection speed is 3.5 m/s,the internal defects of the die castings of the AE44 magnesium alloy die castings have the lowest inclusions and the optimum organization and performance.Based on the comprehensive analysis of XRD and EDS,it can be seen that the microstructure of AE44 magnesium alloy consists of?-Mg matrix,bright white granular or rod-like Al₂RE phase,and bright white needle-like Al₁₁RE₃ phase.The existence of these aluminum rare-earth phases effectively hindered grain boundary sliding and crack propagation and improved the mechanical properties of AE44 magnesium alloys.