Study On Technology And Performance Of Lead - Steel Layered Composites Prepared By Low Pressure Casting

Lead-steel laminated composite materials has tremendous application value and development prospect in electrochemical industry, nuclear shielding and other fields, due to the Lead-steel laminated composite materials combines with many excellent characteristics such as the high strength and light weight, good corrosion resistance, good electrical conductivity and outstanding electrochemical performance. However, Pb and Fe have immiscible problem in energetics. Therefore, on the basis of previous research studies, the lead-Sn alloy was used as medium metal to improve the intersolubility between Pb and Fe in the paper.The interface of energy compensation principle was used in the paper to reduce combining free energy between Pb and Fe,with the method of introducing medium metal terne metal between lead and steel, namely through the medium of two metal with Pb, Fe solubility to solve the solubility of Pb-Fe system. The wettability of intermediary and steel plates are calculated at the same time with the aid of the Y-G-G equation for surface tension of liquid and solid interface. Hot-dip process was selected to prepare steel plate coated with terne metal. Then the lead-steel composite material was prepared with the method of low pressure casting composite method,putting the steel plate coated intermediary terne metal into the casting mould and composite with molten lead.The microstructure of interface of lead and steel and elemental concentration distribution can be observed and tested by scanning electron microscope(SEM), energy-dispersive spectrometry (EDS). The phase of lead-steel was tested by the method of XRD, and the composite interface formation mechanism of lead-steel composite material can be analyzed. And the conductivity, interfacial bonding strength, electrochemical property and other properties of lead-steel composites can be tested and analyzed by the four probes method, universal material testing machine and electrochemical workstation. Conclusions are summarized as follows:(1) The wetting angle between Pb-60%Sn and the Pb matrix can be calculated using the Y-G-G equation and the relationship of surface tension and the melting point. The result shows that the witting angle between the Pb-60%Sn and the surface of lead less than 39.9°,the wettability between them is very well, while the witting angle between the transition of medium and steel is greater than 109.1°,the wettability is bad.(2) The results of interface microstructure morphology, concentration distribution of each element of interfacial area of lead-steel laminated composites show that, When the pouring temperature at 380℃,410℃ and the casting mould temperature at 150℃ and 200℃,because of the temperature is suitable,the temperature of pouring and casting mould is not too high neither too low, the terne metal of the steel plate will not uneven distribution and each element has enough time to diffuse. The interface bonding of lead and steel is good at the scope of the temperature. So the wettability between Pb-60%Sn and steel can be improved by coating the scaling powder (NH4Cl:ZnCl2=1.6:1) on the surface of the steel plate.The interface combinative region is composed with solid solution of a-Pb and β-Sn at the side of the lead and ternary alloy Pb-Sn-Fe at the side of the steel.(3) The results of physical conductivity and strength of interface bonding of lead-steel laminated composites show that,The change rule of specific resistance of the samples reduce first and then increase along with the rise of pouring temperature and casting mold temperature. The specific resistance of all samples are higher than Pb-0.2%Ag,except the samples of A2,A3,B2,B3. The fracture part appears on lead substrate in tensile properties test which explain that the interface bonding strength of lead-steel composites is higher than the tensile strength of lead substrate.(4) The results of the test of electrochemistry and corrosion resistance performance show that, because of the temperature of pouring and casting mold of which is suitable,at the same scanning voltage, only the samples A2 and B2 have the higher electric current density,and at the same electric current density, only the samples A2 and B2 have the lesser polarization potential. After corroded 100h, the corrosion rate of lead-steel laminated composites is 17.2g/m2·h and the corrosion rate of Pb-0.2%Ag alloy is 35.83g/m2·h,the former is about 48% of the latter,so the lead-steel laminated composites have good corrosion resistance performance.