| Under the background of energy saving,environmental protection and lightweight,the application prospect of aluminum alloys is broad.With the continuous development of global transportation industry,cast hypereutectic Al-Si alloy has been widely used in automotive industry because of its good wear resistance,high specific strength and high temperature resistance.It is of great significance to alleviate the contradiction between increasing resources and environment and to improve energy utilization.However,in recent years,accompanied by many major traffic accidents caused by material failure,automotive parts have high potential safety hazards,and the requirements for the performance of automotive engine piston,brake pad and other safety components materials are constantly improving.Therefore,a new type of high-performance,reliable casting hypereutectic Al-Si alloy and its application are developed.Safety evaluation is the premise to promote the development of automobile industry in the future.The purpose of this project is to develop a kind of high-strength,heat-resistant and high-silicon aluminium alloy material,which can be used for safety components such as piston and brake pad of automobile engine.By formulating new technology and new safety evaluation criteria,it can provide technical support for the development of this alloy.Based on the as-cast hypereutectic Al-Si alloy B390,the microstructure and mechanical properties of the alloy were systematically studied.The alloy was optimized by optimizing its composition.On the one hand,a large number of high-temperature unstable ?-Al2 Cu phases and long needle-like ?-Fe phases were removed from the alloy,and more high-temperature stable ?-Al3 Cu Ni phases were introduced to improve the alloy's high-temperature stability.On the other hand,the disappearance of a large number of ?-Al2 Cu phases and long needle-like ?-Fe phases can effectively shorten the solidification interval of the alloy,inhibit grain growth,refine the coarse primary Si phases and other precipitates in the alloy,and thus improve the properties of the alloy.Firstly,B390 and #390 alloys were prepared by metal mould casting.The types and characteristics of precipitated phases of the two alloys were determined by phase diagram analysis and microstructure characterization.The results show that the structure of as-cast B390 aluminium alloy is coarse,mainly consisting of polygonal block primary Si phase,long needle-like ?-Fe phase and coral-like ?-Al2 Cu phase,while as-cast #390 aluminium alloy is combined.The metallographic structure is relatively fine,the phases of beta-Fe and ?-Al2 Cu disappear and the phase of ?-Al3 Cu Ni appears,and the properties of #390 alloy at room temperature,200? and 300? are better than those of B390 alloy.Then,two kinds of alloys were die-casting,and the effects of die casting process on the microstructure and mechanical properties of the alloy were studied.The effects of die casting process parameters and cooling rate on the silicon-poor zone(wear resistance)on the surface of B390 hypereutectic Al-Si alloy provide theoretical support for improving the surface wear resistance of automotive safety components such as engine piston and brake pad.The results show that the structure of die-cast B390 aluminum alloy is refined,the ?-Fe phase changes into Chinese character shape of skeleton,and the short rod-like phase of ?-Al2 Cu disperses,which will intertwine into larger blocks.The precipitated phases of die-cast #390 alloy are finer,and there are more Chinese character-like ?-Al3 Cu Ni phases with uniform network distribution and Chinese character-like skeleton alpha-Fe phases.The tensile properties of die-cast Al alloy are better than those of B390 Al alloy at room temperature.Finally,the high temperature safety fatigue properties of two alloy die castings are evaluated.The fatigue properties of the two alloys were tested by different stress amplitudes at 350?.The macro-high temperature fatigue properties of the two alloys were evaluated by the peak displacement curve,stress-displacement hysteresis curve,S-N curve and equation simulation during the fatigue cycle.The high temperature fatigue damage behavior and strengthening mechanism of the two alloys were further studied based on the analysis of their fatigue fracture surface and side microstructures.The conclusions are as follows: Compared with,die-cast B390 and #390 aluminum alloy has lower steady-state growth rate k value and fatigue strength index.The area of stress-displacement hysteresis curve has little change,higher fatigue cycle life and better fatigue performance of die-cast Al alloy.Compared with ?-Al2 Cu phase in die-casting B390 alloy,the stable ?-Al3 Cu Ni phase in #390 alloy can improve the high temperature fatigue properties of the alloy.Coarse primary Si phase and acicular and massive intermetallic compounds are important factors for accelerating crack initiation and propagation and reducing fatigue properties of alloys.Introducing high temperature strengthening phase into alloys is an important means to improve high temperature fatigue properties of alloys. |
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