| The improvement of engine performance requires higher wear resistance and heat resistance of the piston.Therefore,it is necessary to develop the aluminum silicon alloy piston with higher performance.In this paper,eutectic Al-Si alloy and the hypereutectic Al-Si alloy(w(Si)=20%)were studied respectively to develop high performance Al-Si alloy piston material by modification treatment,multiple alloying and heat treatment.The main results and conclusions are as follows:(1)The effect of rare earth La and Sr on the modification of eutectic Al-Si alloy was studied by changing the content of metamorphic elements.The results show that when1.2% La is added,the eutectic silicon changes from the needle sheet to the short rod shape,and the average size decreases from 84 ?m of no modification to 38 ?m.When adding 0.06%~0.08% Sr,the eutectic silicon changed from needle like to fiber,the average size dropped significantly to about 2?m,the number increased significantly and the distribution was uniform.For eutectic Al-Si alloys,Sr has a much better deterioration than rare earth La.(2)The effect of alloying on the mechanical properties of eutectic Al-Si alloy was studied.Cu,Ni,Mg,Ti,and Zn were used for the multi-alloying.The addition amount of Cu is 3.0% to 3.5%,the addition amount of Ni is 1.0% to 3.0%.The results show that with the increase of element content,Cu can improve the strength of the alloy at room temperature and improve the high temperature strength of the alloy greatly,Ni can improve the room temperature properties,especially the high temperature strength of the alloy under the modification of 0.06% Sr,510 ? solution for 6h and 185 ? aging for 6h.When the content of Cu is 3.5% and the content of Ni is 2.0%,the tensile strength of the eutectic Al-Si alloy is 303.06 MPa at room temperature,the high temperature tensile strength at 300? is 137.74 MPa and Rockwell hardness(HRB)is81.7 after modification and heat treatment.(3)The effect of heat treatment on microstructure and properties of the eutectic Al-Si alloy was studied.The results show that the solution heat treatment can significantly improve the morphology and distribution of eutectic silicon.Under condition of the solution at 510 ? for 6h,the size of eutectic silicon became smaller and the edges and corners tend to round the whole.After aging at 185 ? for 6h,the number of alloy strengthening phase and alloy hardness are increased,the distribution is uniform,the edges and corners are more rounded.(4)The effects of P modification and P+La complex modification on the micro--structure of hypereutectic Al-Si alloy was studied by changing the content of metamorphic elements.The results show that when 0.06% P is added,the average size of the primary silicon is decreased from 129?m of no modification to 29?m,the shape factor is increased from 0.21 to 0.82,and the number is increased and the distribution is uniform.And 0.06%P +0.9%La makes the structure of primary silicon and eutectic silicon obtain the best compound modification effect at the same time.(5)The effects of multicomponent alloying on the mechanical properties of hypereutectic Al-Si alloy piston were studied by using Cu,Ni,Mg,Ti and Zn.The addition amount of Cu is 1.0%~3.0%,the addition amount of Ni is 1.0% ~ 1.5%.The results show that with the increase of element content,Cu can improve the strength of the alloy at room temperature and improve the high temperature strength of the alloy greatly,Ni can improve the room temperature properties,especially the high temperature strength of the alloy under the complex modification of 0.06%P +0.9%La,510 ? solution for 6h and 185 ? aging for 6h.When the content of Cu is 3.0% and the content of Ni is 1.5%,the tensile strength of the hypereutectic Al-Si alloy is242.62 MPa at room temperature,the high temperature tensile strength at 300? is127.95 MPa. |
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