Effect Of Microalloying (Sc,Ti,V,Zr) On Creep Properties Of Piston Aluminum Alloy

Multi-component Al-Si alloy is one of the most widely used piston alloys.When the engine is operating,the top of the piston is directly contacted with high-temperature gas and withstands high pressure.The creep of piston alloy under high temperature and long-term load seriously affects the service life of the piston.In this paper,piston aluminum alloy developed by the research group is taken as the research object.Trace elements Sc,Ti,V,and Zr were added to the alloy separately and in combination.Optical electron microscopy（OM）,scanning electron microscope（SEM）,energy spectrum analysis（EDS）,room temperature tensile,high temperature tensile,creep testing and other analytical testing methods were used to systematically study the microstructure of the piston aluminum alloy and performance impact.The effects of trace elements on morphology and growing size ofα-Al phase,primary silicon phase and Al₃Cu Ni phase in the alloys were discussed.And the influence of microstructure evolution on the mechanical properties of the alloy was analyzed.On this basis,the creep resistance of the alloy was studied systematically,and the mechanism of improving the creep resistance of alloys was summarized by the addition of trace elements.The main research contents of the full text are as follows:（1）After adding trace elements Sc,Ti,V,and Zr alone,the sizes of theα-Al secondary dendrite spacing were reduced to varying degrees.Among them,the Sc-added alloy had the smallest dendrite spacing with a size of 11.61μm,which is 31.9%smaller than that of the matrix.After adding trace elements Sc and Ti,Sc₂Ni₇and Ti-rich phases were generated in the alloy.These two phases could prevent the primary silicon from growing,which refined the primary silicon.The primary silicon size of the Sc-added alloy was reduced by 16.9%compared with the base alloy.And the Ti-added alloy was reduced by 10.9%.The Al₃Cu Ni phase in the Sc-added alloy and the Zr-added alloy underwent granulation.After adding trace alloy elements,the high-temperature tensile strength of the alloy had been improved to varying degrees.Among them,the high-temperature tensile strength of the Ti-added alloy had increased the most,increased by 23.9%;（2）After adding Sc+Ti,Sc+Zr,and Sc+V,the secondary dendrite spacing ofα-Al and primary silicon size in the alloy decreased to varying degrees,of which Sc+Ti alloy decreased the most.At the same time,it was found that Sc₂Ni₇phase,Ti-rich phase,and Al Si Ti phase appeared in the compound-added Sc+Ti alloy.The（Sc,Zr）₂Ni₇phase containing a small amount of Zr appeared in compound-added Sc+Zr alloy.In addition to the Sc₂Ni₇phase and V₅Si₃phase,（Sc,V）₂Ni₇phase was found in the compound-added Sc+V alloy.The morphology of Al₃Cu Ni phase clusters of different alloys had changed to varying degrees.Among them,Al₃Cu Ni phase clusters in the compound-added Sc+Ti alloy were more uniformly distributed,and were connected to the Sc₂Ni₇phase and Ti-rich phase,forming a semi-closed network structure.The Al₃Cu Ni phase in the compound-added Sc+Zr alloy was distributed radially,which had the（Sc,Zr）₂Ni₇phase as the core.The cluster distribution of Al₃Cu Ni phase in compound-added Sc+V alloy was more dispersed and smaller in size.The room temperature and high temperature tensile strength of the alloys were increased after the addition of trace elements,and the room temperature and high temperature strength of the compound-added Sc+Ti alloy were the highest;（3）Adding trace elements Sc,Ti,V,and Zr alone can significantly improve the creep resistance of the alloys,and the creep resistance of the Sc alloy is the best.After compound addition of Sc+Ti,the creep rate decreased to 6.09×10^-6s^-1.The creep mechanism of the alloys are all dislocation climbing.The fracture mechanisms of the alloys are all ductile fracture.The Al-Cu-Ni phase in the Sc-added alloy was granulated to form many granular nanophase Al₂Cu.The number of Al₂Cu nanoparticles in the compound-added Sc+Ti alloy is larger than that in Sc-added alloy,and the size is smaller,so the compound-added Sc+Ti alloy is creep resistant performance is better than the Sc-added alloy.When the temperature is constant,the steady-state creep rate of the alloys increases as the applied stress increases.At the same time,the creep life of the alloys decreases,and its creep resistance also decreases.Adding trace elements can reduce the stress sensitivity of the base alloy under high stress.