Numerical Computation Of Mg/Al Liquid-Solid Interface

The single material can't satisfy the needs of using with more and more complex environment, that make the different materials bonding more important. Magnesium alloy and Aluminum alloy are the most wide light-weight materials. But they are easily oxidizable materials, very different thermal expansion coefficient, and easily reaction form brittle intermetallic compounds. This material properties increase the difficulty of Magnesium alloy and Aluminum alloy bonding. In this paper, the key technology of process, which make liquid Mg alloy pressure casting on solid Al alloy or liquid-solid compound of different metals, is studied in theory and experiment. (1) remove the oxide on the solid Al (alloy) surface; (2) simulate the flow of liquid Mg alloy on the solid Al alloy by using finite element method; (3) compute the residual stress of interface between liquid Mg alloy and solid A1 alloy by using finite element method; (4) study the atom diffusion and enrichment of interface between liquid Mg alloy and solid Al alloyby using molecular dynamics.(1) Zincate surface treatment and electro-galvanizing can remove the oxide layer of solid Al and A1 alloy, and get the effective Zn layer which satisfy the requirement of liquid-solid compound casting process. The optimized process parameters metallurgically bonded interface of pure Mg (or AM60) and surface treated pure Al (or A390) are obtained, and the interfacial strength is 60.6 MPa.(2) The spread of AM60 drop on the A390 substrate is gotten by using CFD and VOF,and representation this by using spread factor. According to the spreading factor's variation, this impact process can be divided into several steps: spreading step,retracting step, and oscillating step, equilibrium step. As for the influence of the drop impact speed, the drop spread speed and the spread diameter on the substrate increased correspondingly when the impact speed increased. The low impact speeds have almost no influence at the equilibrium step due to almost the same spread factors. The diameters of drop have an obvious influence on the retracting step, and oscillating step,while the spread factors were almost same for the spread and equilibrium steps. There are the same spread rates in the spreading step for the cases of the substrate with different temperature. The higher the temperature of the substrate is, the larger the spread diameter can be obtained, while they may take more time for the oscillating step and equilibrium step. These research findings can be further used to guide the optimal control of such a compound casting.(3) Through FEM and element birth and death technology, the heat-mechanical coupling of AM60/A390 can get the residual stress distribution. The results show the stresses are tensile and compressive of AM60/A390, respectively, during cooling process. Based on the structural features of sample, the stress concentration and transformations of tensile and compressive stresses appears on the edges, where have the flaws like cracks. The different thicknesses of Mg and preheat temperatures of Al substrate are studied to get the reasonable compound casting process parameters. The larger thickness of Mg generates larger residual stress. The large preheat temperature can decrease the difference of temperature between Mg and Al, and reduce the residual stress of samples,but the higher preheat temperatures can result in higher temperatures of samples,and produce the larger residual stress during cooling process. Besides that,the surface of A1 substrate appear fusion phenomenon with high preheat temperature,which lead to generate many brittle phase on interface, and the lower preheat temperatures reduce the wettability between liquid Mg and solid Al substrate. With the experiment and simulation results, the reasonable preheat temperature is to heat for 90s in 700 ? furnace temperature.(4) The atom distribution, diffusion coefficient, and length of interface between pure Mg and pure Al are studied by using MD and experiment. The results show the length of Al atoms in Mg is larger than Mg atoms in Al, that is the interface of Mg is thicker than Al. Besides that, the diffusion coefficient of Mg is larger than Al's by fitting the coordinate data of atoms. There are similar trends of interface atoms density between Mg and Al by using EPMA and MD. Through comparing the interface thicknesses with different time of MD simulation and function computation, the results are very similar.Those validate the simulation model is reasonable. The time of diffusion is about 1.94s by computing the function of interface thickness and diffusion time.