First Principle Study On An AlΣ5 Grain Boundary With Si Segregated

Al-Si alloys are polycrystalline materials, whose mechanical property is closelyrelated to the cohesion of the grain boundary. As well, the cohesion is highly dependenton the local atomic structure which is highly impacted by the impurity atom thatsegregates at the grain boundary. In this paper, we studied the mechanical property of thepure AlΣ5(012)[100] grain boundary and the systems with Si segregated to enhance andimprove the mechanical properties of Al-Si alloys.First of all, we established the AlΣ5(012)[100] grain boundary model by thecoincidence site lattice model theory. Secondly, through the optimization of the modelstructure, we calculate the total energy of each system and the total energy of an isolatedSi atom by using the VASP package, by which we determine the placeholder tendency ofSi atoms, when the Si atom segregate at the Al grain boundary. Finally, we implementtensile test at the Al grain boundary by using the first principles method based on densityfunctional theory and generalized gradient approximation with the stress tensilesimulation method. We get the stress of pure Al grain boundary system and the grainboundary systems with Si segregated with the strain Increased, so that we get thetheoretical tensile strength of each system. We analysised the change of the theoreticaltensile strength quantitatively and studied the mechanisms of reduce of the cohesion ofgrain boundary qualitatively.In this paper, we pointed out the theoretically possible way to overcome thissegregation, which laid the theoretical basis for materials modification. The researchenriches and improves the mechanical properties of Al-Si alloy materials database, andprovides theoretical basis for the application of the material, at the same time.