Study On Grain Refinement And Properties Of Near Eutectic Al-Si Alloy

Al-Si cast aluminum alloys are the most widely used cast aluminum alloy in industrial production at present.Among them,near eutectic Al-Si alloy has excellent comprehensive properties,good wear resistance,corrosion resistance,low thermal expansion coefficient and linear shrinkage ratio,and is widely used in the automotive industry.With the development of industry,the performance requirements of alloys in various fields are constantly improving.It is of great significance for the application of alloys to further improve the performance of neareutectic Al-Si alloys by fine grain strengthening.This paper mainly studies the refinement of near eutectic Al-Si alloy and its influence on the microstructure and properties of the alloy.The effects of Al-Ti-C-B master alloy,Al-Ti-C master alloy and cryogenic treatment on the grain size,microstructure and properties of near eutectic Al-Si alloys were studied by selecting Al13Si-1Cu alloy and Al-12Si-4Cu-2Ni-1Mg alloy as the research objects.The role of primary silicon in grain refinement was also explored.The mechanism of grain refinement is further expanded.The main research contents of this paper are as follows:(1)Effect of Al-Ti-C-B master alloy on grain size,microstructure and properties of near eutectic Al-Si alloyAdding Al-Ti-C-B master alloy to Al-13Si-1 Cu alloy,it is found that the master alloy has a good grain refinement effect on Al-13Si-1Cu alloy,and the amount of primary silicon increases during the observation of the alloy microstructure.Further studies on primary silicon show that TiB2 particles in Al-Ti-C-B master alloy can nucleate diphase with AlP to improve the nucleation efficiency of AlP for primary silicon.Adding Al-Ti-C-B master alloy to Al-12Si-4Cu-2Ni-1Mg alloy,it is found that the master alloy has obvious grain refinement effect on Al-12Si-4Cu-2Ni-1Mg alloy,and has a great influence on the three-dimensional structure of the microstructure of the alloy.After adding 2%Al-Ti-C-B master alloy,The connectivity rate of the second phase of the alloy reaches 19.38%,compared with the original alloy,the connectivity rate of the second phase of the alloy is increased by 58.3%.The connection between the alloy phase and eutectic silicon in the alloy is closer.The addition of master alloy can also improve the tensile and fatigue properties of the alloy at room temperature.With the addition of 1.5%Al-Ti-C-B master alloy,the tensile strength and elongation of Al-12Si-4Cu-2Ni-1Mg alloy can reach 370 MPa and 0.75%at room temperature,respectively.Compared with the original alloy,the tensile strength and elongation of Al-12Si-4Cu-2Ni-1Mg alloy can be increased by 8.2%and 44.2%,respectively.When the addition amount of Al-Ti-C-B master alloy is 1.0%,the cycle times of the alloy can reach 3.7×105 times and 2.1×105 times at the stress amplitude of 30 MPa and 40 MPa,respectively,which is greatly improved compared with the original alloy of 1.1×105 and 1.4×105.(2)Effects of Al-Ti-C master alloy on grain size,microstructure and properties of near eutectic Al-Si alloyAl-Ti-C master alloy was added to Al-12Si-4Cu-2Ni-1Mg alloy,and the introduced TiC particles had a good grain refining effect on the alloy.During the observation of the alloy microstructure,the dual-phase nucleation phenomenon of TiC and AlP particles was found in the primary silicon core.Al-Ti-C-B master alloy can also improve the tensile properties of the alloy at room temperature.The temperature tensile properties of Al-Ti-C master alloy are also improved.The tensile strength of the alloy at room temperature increases with the addition of Al-Ti-C master alloy.When the addition amount is 2%,the tensile strength of the alloy reaches 360MPa,which is 6%higher than that of the original alloy 339MPa.The elongation at room temperature is also improved,and the elongation is the highest when the addition amount is 1.5%.Compared with the original alloy elongation of 0.52%increased by 15.4%.(3)Study on the effect of primary silicon on the refinement of near eutectic Al-Si alloysCombined with the study on the refinement of near eutectic Al-Si alloy by Al-Ti-C-B master alloy and Al-Ti-C master alloy,it is found that both of the two master alloys have the refinement effect on near eutectic Al-Si alloy,and both of them have the refinement of primary silicon and the increase of primary silicon in the refinement process.This indicates that the grain refinement of Al-Ti-C master alloy and Al-Ti-C-B master alloy is not only realized by the refinement of α-Al,but also affected by the refinement of primary silicon.Therefore,it is of great significance to improve the nucleation efficiency of AlP for primary silicon by using TiB2 particles and AlP for grain refinement of near eutectic al-si alloys,which can be used as a research direction for refinement of Al-Si alloys,especially some al-Si alloys with higher silicon content.In previous studies,many scholars have studied the biphase nucleation of primary silicon.However,the current research on the biphase nucleation of primary silicon has not been extended to the refinement of primary silicon and the refinement of alloy grains.We can study the biphase nucleation of TiB2,TiC,AlB2 and AlP particles.The coordination of master alloy is better for refining high Al-Si alloy with high silicon content.(4)Effect of cryogenic treatment on grain size and properties of near eutectic Al-Si alloyBy comparing the effects of Al-Ti-C-B master alloy and Al-Ti-C master alloy on the grain,microstructure and properties of the near eutectic Al-Si alloy,We choose Al-Ti-C-B master alloy as the master alloy used in the cryogenic treatment experiment,with the addition amount of 1%,and the treatment method is as follows:Solution treatment at 510℃ for 2h+cryogenic treatment+aging treatment at 180℃ for 8h.After different time after cryogenic treatment of the alloy corrosion found that cryogenic treatment time is 4 h,8 h,16 h,grain size of alloy basic did not change,after cryogenic time reach 24 h,alloy grain refinement is more apparent.Cryogenic treatment can improve the tensile strength and elongation of the alloy at room temperature.Before cryogenic treatment,the tensile strength and elongation of the alloy at room temperature are 354MPa and 0.71%,respectively.After cryogenic treatment for 24h,the tensile strength and elongation of the alloy at room temperature can reach 378MPa and 0.87%,respectively.The room temperature tensile strength increased by 6.8%and elongation increased by 22.5%.