Study On Hot Tearing Behavior Of Al-5Cu Alloy

Aluminum-copper（Al-Cu）alloys are high-strength casting aluminum alloys,which are widely used in aviation,aerospace,military,automobile and other fields,owing to good ductility,plasticity,machinability and moderate stress corrosion resistance.However,due to the wide range of crystallization temperature and large solidification shrinkage,Al-Cu series alloys are prone to hot tearing and other defects in the casting process,which limit their wide application.Therefore,it is of great practical significance to study the hot tearing susceptibility of Al-Cu alloys.In this paper,the combined method of Procast simulation software and"T-type"hot tearing test system was used to study the influence of pouring process（casting temperature,mold temperature,indenter height）on the hot tearing susceptibility of Al-5Cu alloy through orthogonal test.Based on the theoretical model of Clyne-Davies,the effects of low-frequency alternating magnetic field current intensity and magnetic field frequency on the hot tearing susceptibility of Al-5Cu alloy were studied respectively by applying low-frequency alternating magnetic fields with different current intensities（0A,5 A,10 A,15 A）or different frequencies（0 Hz,5 Hz,10 Hz,15 Hz）during the solidification of the Al-5Cu alloy.In the experiment,the hot tearing susceptibility was evaluated by the size of the tearing at the hot joint of the"T-shaped"sample prepared under different conditions,and solidification behavior of the alloy was analyzed by the double-couple differential thermal analysis experiment,the microstructure,grain size,phase composition and distribution morphology of the alloy were analyzed by Zeiss metallographic microscope,scanning electron microscope and X-ray diffraction,which could help to discover the law that affect the hot tearing susceptibility of alloys and reveal the hot tearing mechanism of Al-5Cu alloy.The experimental results showed that the hot tearing susceptibility of Al-Cu alloy first decreased and then increased with the increase of pouring temperature,and the hot tearing susceptibility was the lowest at 710℃when the mold temperature was in the range of 240°C to 280°C and the indenter height was in the range of 150 mm-250 mm.With the increase of mold temperature,the hot tearing susceptibility of the alloy decreased gradually when the pouring temperature was in the range of 690°C to 730°C and the indenter height was in the range of 150 mm to 250 mm.With the increase of the indenter height,the hot tearing susceptibility of the alloy first increased and then stabilized when the casting temperature was in the range of 690°C to 730°C and the mold temperature was in the range of 240°C to 280°C.And the influence degree of casting process on the hot tearing susceptibility of Al-5Cu alloy was:mold temperature>pouring temperature>indenter height.The optimal pouring process parameter combination with the lowest hot tearing susceptibility was A₂B₃C₁:the pouring temperature was 710°C,the mold temperature was 280°C,and the indenter height was150 mm.After applying low-frequency alternating magnetic field during the solidification of Al-5Cu alloy,in the range of 0-15 A or 0-15 Hz,with the increase of the alternating magnetic field current intensity or magnetic field frequency,the hot tearing susceptibility of Al-5Cu alloy decreased first and then increased.When the alternating magnetic field current intensity or magnetic field frequency was 10 A or 10 Hz,the hot tearing susceptibility of the alloy was the lowest.In the range of 0-10 A or 0-10 Hz,as the current intensity or frequency of the alternating magnetic field increases,there is strong forced convection in the molten metallic pool under the action of electromagnetic force,which leads to the fragmentation of dendrites and the grains refinement,optimizes the feeding channels between grains and reduces the hot tearing susceptibility of the alloy.When the current intensity or frequency of the alternating magnetic field are 15 A or 15 Hz,the grains become coarser due to the thermal effect of electromagnetic field,resulting in the deterioration of the feeding channel during solidification and the increase of hot tearing susceptibility.