If the coating is too thin, the resulting composite layer cannot provide protection to the substrate. If it is too thick, it will cause insufficient coating fusion and the resulting composite The layer quality is poor. 2.2 Composition analysis of the composite layer on the surface of the casting In order to study the distribution change of each element from the surface ceramic layer, the alloy layer to the alloy matrix, a line scan analysis was performed on the composite layer, as shown. The composition of the ceramic layer is mainly composed of PbO-ZnO-Na2O low-temperature glass powder, which mainly contains O, Na, Zn, and Pb elements. At the interface between the ceramic layer and the alloy layer, the oxygen element content is significantly increased, mainly due to the interface A certain amount of oxide inclusions. From the distribution curve of magnesium and aluminum elements, except that the aluminum element has a small amount of diffusion into the ceramic layer near the interface, the magnesium element hardly diffuses into the ceramic layer, and the composition changes abruptly at the interface. However, during the transition from the ceramic layer to the alloy layer, it was found that the composition of the low-temperature glass frit did not change abruptly. This can be seen from the distribution curve of the element composition of Pb, Zn, and Na, especially the change trend of the element of Pb and Zn is A gradual decrease process. This shows that in the process of surface compounding, the outer ceramic coating diffuses to the alloy layer after melting, so that the interface realizes metallurgical bonding, which is conducive to improving the bonding strength of the interface. I. XRD analysis of the composite layer on the surface of the composite layer prepared with different alloy coating thicknesses. Fig. Casting of Lost Foam Although the process is simple, the process of metal liquid filling CNC machining is difficult to control, especially many factors in the surface composite process influences. If the process is not properly controlled, it will bring a lot of defects. As shown in the figure, there are two main reasons: on the one hand, during the filling process, the low-temperature glass powder is washed away and is involved in the melt to form inclusions, on the other hand Because the casting temperature is higher, the magnesium alloy is easily oxidized. Once the oxide is caught in the melt, it becomes inclusions after solidification. Therefore, if a high-quality composite layer is prepared, the process must be strictly controlled to reduce paint scouring to reduce defects, control melt oxidation, completely discharge slag during pouring, and avoid oxidation inclusions involved in the melt during the casting process. In short, the control of the lost foam casting process must have certain process equipment as a prerequisite, and then control the process parameters to obtain better results. It is the XRD analysis of the surface composite layer. The AZ91D magnesium alloy matrix is mainly composed of a-Mg and P-vAlnMgn, and the alloy layer has newly formed AbMg2, Al, MgZn phases in addition to the original phases, mainly because of the alloying process In the middle, the molten metal contacts the alloyed coating and melts it. The aluminum content is high at the interface. From the binary phase diagram of Mg-Al, it can be seen that the main products are AbMg2 and Al, and the metal is generated where the aluminum content is low. Inter-compound P-AlMg, such as ab is the XRD diffraction analysis of the surface ceramic layer. The results show that the low-temperature glass frit crystallizes after heating and generates multiple oxide phases. From a thermodynamic point of view, the amorphous state is in a higher freedom The metastable state of energy, under appropriate conditions, must orient the metastable amorphous state with lower energy or the equilibrium crystalline state transition with lower energy. Therefore, after the outer layer of the low-temperature glass frit preformed layer is subjected to the heat transfer of the metal liquid, the energy of the system is reduced to the crystalline state, and a ceramic layer composed of oxide is formed on the surface of the casting. 2.3 The performance analysis of the composite layer on the casting surface shows that the microhardness corresponding to the surface structure is obtained by different processes.
