Study on the synthesis and properties of lead - steel laminated composite materials
|School||Kunming University of Science and Technology|
|Keywords||lead-steel laminated composite media metal micro-alloy layer interfacestructure|
Lead-steel composite has presented tremendous developing potentiality in metallurgical industry and nuclear shielding. Especially in metallurgical industry, lead-steel composite materials have showed attractive application due to their light weight, high mechanical strength and excellent electrochemical characteristic. However, Pb and Fe have immiscible problem in welding process.Therefore, the solubility and weldability problems of Pb and Fe are the key to the application for lead-steel composite material.In order to improve the miscibility between Pb and Fe, It was put forward the interface of energy compensation principle. It was introduced intermediary between lead and steel metal to reducing combining free energy between Pb and Fe, namely through the medium of two metal with Pb, Fe solubility to solve the solubility of Pb-Fe system. The mixing enthalpy of Pb-Sn, Fe-Sn, Fe-Pb,Pb-Sn-Fe are analyzed and calculated by the theoretical model based on Miedema and Toop. 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-solid interface. Hot-dipping was selected to prepare steel plate coated different intermediary. Then a new lead-steel laminated composite material was prepared with the aid of TLP, using vacuum hot-pressing furnace to weld steel plate coated intermediary and lead plate.From the point of experimental analysis, It was tested the interface morphology and interfacial zone products of the steel plate coated intermediary by means of SEM, XRD, OM. It was studied the wettability reaction and kinetic process of liquid tin and steel, and tested the morphology and interfacial area elements distribution of lead-steel laminated composite material. For revealing the interface formation mechanism between lead and steel by using the theory of mathematical model of interface element to simulate the numerical distribution. Finally It was used the three-point bending, four-point probe and electrochemical workstation to inspected the properties of lead-steel laminated composite material. The results show that: (1) The calculation of Pb-Sn-Fe ternary hybrid gibbs (△G＜0) using formal model to greatly improve the thermodynamics mixing soluble of Pb-Fe system for Sn as activity. Fe atom of Steel plate was combined Sn to FeSn2intermetallic compound in the process of hot dipping and the Sn combined with steel as metallurgical type. Then a stable Pb-Sn binary eutectic organization and FeSn2alloying layer was formed in interface of lead-steel composite in the process of vacuum hot pressing diffusion welding as the eutectic reaction of Pb and Sn.(2) For the introduction of intermediary M (Sn, Pb-Sn40%60%,60%,35%Pb-Sn-35%zinc) between lead and steel, diffusion couple of intermediary and lead layer was formed at the first stage of vacuum hot pressing. Tin of intermediary and lead occur eutectic reaction forming instantaneous liquid phase, and Sn in liquid phase occurs dissolution reaction. Pb-Sn binary eutectic organization was formed in subsequent isothermal solidification process. As the diffusion of Pb and Sn at interface, FeSn2intermetallic compound was pushed to the substrate side of lead. Interface was moved toward the steel side with the micro-alloy layer diffusing along the grain boundary. Eventually interface of lead-steel laminated composite material formed a interface structure which was from lead substrate, lead solder eutectic organization area, to the diffusion area of micro-alloy layer and steel substrate.(3) The test results of physical conductive properties, mechanical properties and electrochemical properties of lead-steel laminated composite show that:physical conductivity and mechanical properties of lead-steel the layered composite sample effectively improved with the introduction of medium metal.Combined with the preparation process and interface bonding of lead-steel laminated composite, micro-alloy layer in interface of lead-steel sample decreased with the increasing of temperature or holding time and the resistivity of lead-steel composite gradually reduced. Compared with the same size of Pb-0.2%Ag sample, the average conductivity and flexural strength increased22%～37%and45.4%. Compared with Pb-0.2%Ag alloy, lead-steel composite sample showed low polarization potential, corrosion current density and good catalytic activity.