Effect Of La/Ce On The Microstructure And Properties Of Al-12Si-6Cu-1.5Ni-0.3Cr-1RE Alloy

Cast heat-resistant aluminum alloy is widely used in engine piston because of its high specific strength and low density.At the same time,its casting performance and cutting performance are superior,which conforms to the concept of green environmental protection in today's society.With the continuous development of automobile industry,the requirements of engine performance are also increasing.The traditional piston alloy can not meet the current needs.The lightweight cast heat-resistant aluminum alloy not only helps to reduce the weight burden of the engine,but also improves the working efficiency of the engine.At present,the main way to improve the performance of heat-resistant aluminum alloy is solution strengthening,excess phase strengthening,adding thermal strength elements to produce high temperature strength of the second phase,and then further improve the performance of the material through subsequent heat treatment.In this paper,the effects of rare earth ratio and heat treatment parameters on the structure and properties of Al-12Si-6Cu-1.5Ni-0.3Cr-1RE heat-resistant aluminum alloy were studied.First,the influence of LA/Ce on the microstructure and properties of al-12si-6cu-1.5ni-0.3cr-1re alloy was studied by means of OM metallography,XRD phase analysis,SEM scanning observation and EDS energy spectrum analysis at room temperature and high temperature?300??.The results show that the as-cast Al-12Si-6Cu-1.5Ni-0.3Cr-1RE alloy is mainly composed of?-Al matrix,primary Si phase,eutectic Si phase,?-Al₂Cu phase,?-Al₃Cu Ni and?-Al₇Cu₄Ni phase.The tensile tests at room temperature and high temperature?300??were carried out to study the mechanical properties of the material.The results showed that with the increase of La content,the Ce content decreased.The tensile tests at room temperature and high temperature?300??showed a trend of first increasing and then decreasing,reaching the peak value at 0.8ce-0.2la,and the tensile test results at as-cast state were 173.8Mpa,132.7Mpa,respectively,and the tensile test results at heat treatment state were 173.8Mpa,132.7Mpa,respectively 286.5Mpa,137.8Mpa.In order to further improve the properties of the material,the Al-12Si-6Cu-1.5Ni-0.3Cr-0.8Ce-0.2La alloy was treated with Sr+Ti.The results showed that the eutectic silicon changed from needle like to granular and fibrous,the black coarse strip phase has changed to granular and spherical,and the tensile strength of the cast and heat-treated state at room temperature increased to 237.2Mpa,319.4Mpa.The tensile strength at high temperature?300??was increased to 146.7 MPa and 151.9 MPa.Then,the heat treatment process of the optimized Al-12Si-6.0Cu-1.5Ni-0.3Cr-0.8Ce-0.2La alloy was optimized.The results show that after solution treatment,the primary Si is passivated at sharp angle,the eutectic Si phase is fused to be granular and fine point,and the reticular phase has no large area of aggregation,but it is fused to be short rod distributed on the?-Al matrix,and the coarse strip rare earth rich phase structure is gradually transformed from short rod to block,granular and spherical,the aging treatment has little effect on the optical microstructure of the alloy;The tensile properties of the alloy were tested.With the increase of two stage solution temperature,the tensile strength at room temperature and high temperature?300??first increased and then decreased,and reached the maximum at 530?.With the increase of the two stage solution time,the tensile strength increases first and then decreases at room temperature and high temperature?300??,and reaches the maximum at 2h.The best solution treatment process is 490?×2h+530?×2h.After the optimized solution process,the aging treatment process is further optimized.The tensile strength at room temperature and high temperature?300??first increased and then decreased,reaching the maximum at 200?.With the increase of aging time,the tensile strength at room temperature and high temperature?300??first increased and then decreased,reaching the maximum at 4h.Finally,it is concluded that the best aging treatment process is 200?×4h.Therefore,the best heat treatment process of casting Al-12Si-6Cu-1.5Ni-0.3Cr-0.8Ce-0.2La alloy is 490?×2h+530?×2h?water quenching?+200?×4h.The tensile strength of the alloy under this heat treatment is348.5 MPa at room temperature and 160.4 MPa at high temperature?300??,which is 46.9%and 9.3%higher than that of as-cast.The results of TEM analysis show that the aging effect of two-stage solution is better than that of single-stage solution.