Effects Of Er Content On Hot Cracking And Microstructure Properties Of Al-5Cu Alloy

Al-Cu alloy is used in automotive and aircraft manufacturing,mainly because of its good performance in service,heat treatment can enhance the strength.However,due to its wide crystallization temperature range,hot cracking is easy to occur during casting,and the application range of the alloy is limited.The hot cracking of Al-Cu alloy has become a hot research topic.In this paper,the as-cast microstructure,mechanical properties and hot cracking properties of Al-5Cu alloy（x=0,0.3 wt.%,0.6 wt.%,0.9 wt.%）were studied by wedge casting experiment,optical microscope,differential thermal analyzer and scanning electron microscope.The effect of cooling rate on hot cracking properties and microstructure evolution of Al-5Cu and Al-5Cu-0.6Er alloys was investigated.The relationship between microstructure evolution and properties of Al-5Cu-0.6Er alloy was studied by optimizing the heat treatment process,and the Al-Cu-Er alloy with better properties was obtained.The main conclusions are as follows:（1）With the increase of Er content from 0 to 0.9 wt.%,the casting hot cracking tendency of Al-5Cu alloy decreases first and then increases.Al-5Cu-0.6Er alloy has the lowest casting hot crack tendency.The addition of Er causes the formation of Al₈Cu₄Er phase in the alloy,resulting in a smaller crystallization temperature range of Al-5Cu alloy,improving the fluidity of liquid film at the later solidification stage of the alloy,and reducing the tendency of hot cracking of the alloy.When Er content is more than 0.6 wt.%,due to the generation of Al₃Er phase,the resistance of liquid film fluidity increases and porosity increases,leading to the increase of hot crack tendency in alloy casting.（2）The hot cracking tendency of Al-5Cu alloy changes in the same direction with the cooling rate.As the cooling rate increases,the supercooling degree of the alloy increases,the growth of the second phase between grains is inhibited,and the fluidity of the liquid film becomes worse at the late solidification stage,and the tendency of hot cracking increases.When the cooling rate is 160℃/s,the dislocation density of Al-5Cu-0.6Er alloy is about 1.26 times that of Al-5Cu alloy.The addition of Er increases the dislocation density of Al-5Cu alloy,which increases the thermal cracking resistance of the alloy at the later solidification stage and reduces the hot cracking tendency of the alloy.（3）Under the optimal solution process（535℃/12h）and different aging process（155℃,175℃,190℃）,the corresponding peak aging time of Al-5Cu-0.6Er alloy at 155℃,175℃and 190℃is11h,9h and 6h,respectively.The tensile strength corresponding to peak aging is 296 MPa,287 MPa and 250 MPa,and the yield strength is 201 MPa,196 MPa and 171 MPa,respectively.The precipitation of Al₂Cu phase during aging is the main reason for the improvement of the properties of Al-5Cu-0.6Er alloy.