Effect Of Mg On The Formation Of Intermetallic Compounds And Hot Cracking Tendency Of Al-Cu Alloy

Hot cracking is one of the main defects of cast Al-Cu alloy,and it is also an important factor restricting the performance potential of the alloy.The hot cracking mechanism of Al-Cu alloy has been studied,and some hot cracking phenomena have been explained,especially the role of intermetallic compounds with low melting point in hot cracking.At present,there are mainly three theories about the hot cracking mechanism of alloy:intergranular bridging theory,liquid film theory and solidification shrinkage compensation theory.However,the relationship between the composition of low-melting intermetallic compounds on the grain boundary of Al-Cu alloy and the occurrence of hot cracking remains to be further studied.The hot cracking of the alloy is closely related to its solidification thermodynamics and kinetics.It is of great significance to further improve the hot cracking tendency of Al-Cu alloy by further understanding the solidification thermodynamics and kinetics.However,the relationship between the composition of intermetallic compounds with low melting point and the hot cracking of Al-Cu alloy in the late solidification stage is still to be further studied.In this thesis,Al-4.4Cu-0.15Zr-Xmg alloy is used to study the effect of Mg content on the intermetallic compound and the hot cracking tendency of the alloy.Using Jmatpro software to simulate the solidification process of aluminum alloy,the relationship between the amount of intermetallic compound and the amount of Mg element was analyzed,and the Clyne-Davies model was used to predict the hot cracking tendency of aluminum alloy.Firstly,SEM,TEM,EDS,XRD,DSC and EPMA were used to analyze the effect of Mg addition on the formation of intermetallic compounds of Al-4.4Cu-0.15Zr-x Mg alloy.The results show that Al₂CuMg phase,Al₂Cu Mu phase,Al CuMg phase and Al₃Zr phase can be formed in the alloy during solidification.The number of Al₂CuMg phase increased first and then decreased with the increase of Mg content,the number of Al₂Cu phase decreased,the number of Al CuMg phase increased gradually,and the number of Al₃Zr phase changed little.When the content of Mg was1.68-1.71Wt.%,the number of Al₂CuMg phase was the highest,and when the content of Mg was1.68Wt.%,Al₂Cu disappeared.The Al CuMg phase appeared when Mg content was 1.71Wt.%,and the grain size of the alloy was small and the microstructure was uniform.Secondly,JMat Pro software was used to simulate the solidification process,and the comparative analysis of solidification data showed that the liquidus temperature of the alloy decreased slightly with the increase of Mg content,but the change range was not large,indicating that the addition of Mg element could reduce the solidification temperature range of the alloy.The volume fraction of the unsolidified liquid at the grain boundary has the same tendency as the HSC value.The formation quantity of Al₂CuMg phase has an opposite trend to HSC value,the formation quantity and temperature of Al₂Cu phase have an opposite trend to HSC value,and the formation quantity and temperature of Al CuMg phase have the same trend to HSC value.The thermal cracking resistance of the alloy can be improved by controlling the amount and temperature of low melting point intermetallic compounds.Finally,the relationship between the content of Mg and the hot cracking tendency of the alloy was further analyzed by experiments.The results show that when the content of Mg in the alloy is1.0%-2.5wt.%,the CSC value decreases first and then increases with the increase of the content of Mg,and the CSC value is the minimum when the content of Mg is 1.7wt.%,and the sensitivity of hot cracking and hot cracking tendency are the minimum.The experimental results are in good agreement with the simulation results.