Study On The Process Of Al-Al₄Ca Composite

In this paper,the Al-Ca binary alloy with different content of Ca is studied,the mechanism of the second phase transformation of the alloy was explored,and the influence of the second phase transformation on electrical conductivity,hardness and tensile properties of the alloy was analyzed.The corrosion resistance of the alloy was studied by weight loss and electrochemical tests.In addition,by adding B element to hypoeutectic Al-5wt.%Ca alloy,the effects of boration,holding time and cooling rate on the structure and properties of the alloy were studied,and then Al-Al4Ca composite for high voltage transmission was developed.The main conclusions of this paper are as follows:(1)The second phase of Al-5wt.%Ca alloy is mainly about Al4Ca,and the morphology is divided into lamellar and acicular.In addition,electrical conductivity of Al-5wt.%Ca alloy as cast is 40.3%IACS,which is 1.5 times higher than Al-9wt.%Ca alloy as cast.(2)When Al-Ca alloy is kept at low temperature,martensitic transformation occurs in Al4Ca phase,which improves the electrical and mechanical properties.When Al-5wt.%Ca is kept at 150? for 1h,electrical conductivity of the alloy increases to 43.9%IACS,the tensile strength reaches 255.5MPa,the yield strength reaches 148.7MPa,and the elongation reaches 4.6%.(3)After high temperature holding for a period of time,the morphology of Al4Ca phase changes from lamellar to granular.After holding for 8h at 570?,the degree of spheroidization is the highest,and then it begins to coarsen.Electrical conductivity is directly proportional to the degree of spheroidization.(4)The corrosion of Al-Ca binary alloy belongs to pitting corrosion.The corrosion rate of the alloy is close to 0.01mm/a,which belongs to grade II corrosion with good corrosion resistance.This is due to the fact that the potential of Al4Ca is relatively negative compared with that of Al-Ca binary alloy matrix and it is easy to be preferentially corroded.(5)Adding B to hypoeutectic Al-5wt.%Ca can improve electrical conductivity and mechanical properties of the alloy.The removal efficiency of boron is as high as 79.41%,and electrical conductivity is increased to 50.9%IACS.Too much B will refine the ?-Al grains and reduce electrical conductivity of the alloy.(6)After boron treatment,when the melt is kept at 750? for 40min,electrical conductivity and hardness of the alloy are the best.Electrical conductivity of the boron alloy increased to 51.7%IACS after being kept at 570? for 8 hours.(7)Because the cooling rate is fast,the grain size of a-Al is smaller.The fast cooling rate also make the distance between Al4Ca layers is shorter than before.These changes reduce electrical conductivity and improve the hardness.(8)After boron treatment,the tensile strength and yield strength of the alloy decreased slightly,but the elongation increased significantly,reaching 11.9%.The fracture of the alloy is caused by the large difference of plastic parameters between the matrix Al and the second phase Al4Ca.