Microstructure And Properties Of Al-Si Alloys With High Manganese Content And Their Composites Under Different Vibration Fields

With the rapid development of the transportation field,in order to adapt to the development trend of green casting for energy saving and emission reduction,traditional cast aluminum alloys cannot meet the requirements for new high-power diesel engine heat resistant aluminum piston alloys.Alloying,compounding,and applying multi-field coupling of aluminum piston alloys are effective ways to improve the heat resistance aluminum piston alloys.This thesis takes the Al-Si-Cu-Ni-Mg alloy with high Mn content as the research object,applies ultrasonic and mechanical vibration fields on near liquidus of the Al-Si pistion alloys,refines the metamorphic manganese-rich phases,and makes the nano-ZrB₂particles uniformly distributed.A new type of heat-resistant aluminum-silicon piston alloy material is achieved.The microstructure and room temperature and high-temperature mechanical properties of the aluminum-silicon piston alloys under various process conditions have been studied,and the following results have been obtained:(1)The microstructure and mechanical properties of aluminum-silicon alloy with high Mn content under the action of gravity field,single ultrasonic field,ultrasonic+mechanical vibration single field are studied.It is found that the vibration field does not change the composition of the manganese-rich phase,and the manganese-rich phases were all Al₁₅Mn₃Si₂phases.Under the action of gravitational field,the manganese-rich phase has a developed dendritic structure.When the ultrasonic field,ultrasonic+mechanical vibration single field is applied,the manganese-rich phase in the alloy becomes small,and the primary silicon is refined and rounded and distributed uniformly at the same time.As a result,the room temperature and high temperature mechanical properties of the alloy have been significantly improved.However,after the alloy undergoes a single field of ultrasonic+mechanical vibration,the microsturctuture is excessively refined.Compared with the single ultrasonic field,the high temperature strength of the alloy under the single field of ultrasonic+mechanical vibration decreases.The tensile tests at room temperature and350°C shown that tensile strength with applying the single ultrasonic field for 2 minutes is270MPa and 113MPa,respectively,the yield strength is 150MPa and 107MPa,respectively,and the elongation is 2.3%and 4.1%,respectively.The high temperature strength of the Al-Si-Cu-Ni-Mg-Mn piston alloys under the single ultrasonic field are higher than commercial piston aluminum alloys.(2)The microstructures and mechanical properties of aluminum-silicon alloys with high Mn content under the ultrasonic+mechanical vibration coupling field are studied.It is found that the size of manganese-rich phase and primary silicon in the alloy under the action of horizontal mechanical vibrationbecomes more smaller and distributed more uniformly,compared with that in the alloys under the action of vertical mechanical vibration.The best mechanical properties of the Al-Si-Cu-Ni-Mg-Mn piston alloys applying horizontal mechanical vibration for 4 minutes can be obtained at room temperature and high temperature under the action of the coupled field with Thetensile strength value is 315MPa and 118MPa,respectively,the yield strength was 184MPa and103MPa,respectively,and the elongation is 3.0%and 5.4%,respectively.(3)The microstructures and mechanical properties of aluminum-silicon alloy with high Mn content enhanced by nano-sized ZrB₂particels under the action of gravity field,single ultrasonic field,ultrasonic+mechanical vibration coupled field are studied.In gravity die cast alloys,the agglomeration of ZrB₂particles is serious.After ultrasonic field,ultrasonic+mechanical vibration coupling field treatment,ZrB₂agglomeration phenomenon was improved,and the distribution of ZrB₂in the aluminum matrix is more uniformly.As a result,the room temperature and high temperature mechanical properties of aluminum matrix composites have been greatly improved,which is mainly due to dispersion strengthening and dislocation strengthening of nano-sized ZrB₂partilces.The alloy can be obtained the best mechanical properties at room temperature and high temperature when the coupled field treatment temperature is 610?.The tensile strength of the coupled field treatment alloys is 359MPa and 127MPa,respectively,the yield strength is 284MPa and 125MPa,respectively,and the elongation is 4.3%and 5.0%,respectively.